Update mvn publish plugin, version bump

Revert transition module package name change
Fixes tests
2020-05-04 18:07:12 -05:00 · 2020-05-04 17:56:53 -05:00 · 2020-05-04 17:55:11 -05:00 · 2020-05-04 17:05:48 -05:00 · 2020-05-04 17:05:07 -05:00 · 2020-04-27 15:59:31 -05:00
219 changed files with 11356 additions and 3423 deletions
@@ -5,10 +5,10 @@
 .checkstyle

 # IntelliJ IDEA
-.idea
 *.iml
 *.ipr
 *.iws
+*.idea/dictionaries
 classes
 gen-external-apklibs

@@ -0,0 +1,8 @@
+/libraries
+/runConfigurations.xml
+/misc.xml
+/vcs.xml
+/workspace.xml
+/caches
+/gradle.xml
+/modules.xml
@@ -0,0 +1,129 @@
+<component name="ProjectCodeStyleConfiguration">
+  <code_scheme name="Project" version="173">
+    <JetCodeStyleSettings>
+      <option name="NAME_COUNT_TO_USE_STAR_IMPORT" value="2147483647" />
+      <option name="NAME_COUNT_TO_USE_STAR_IMPORT_FOR_MEMBERS" value="2147483647" />
+      <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
+    </JetCodeStyleSettings>
+    <codeStyleSettings language="XML">
+      <indentOptions>
+        <option name="CONTINUATION_INDENT_SIZE" value="4" />
+      </indentOptions>
+      <arrangement>
+        <rules>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>xmlns:android</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>xmlns:.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>BY_NAME</order>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*:id</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>http://schemas.android.com/apk/res/android</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*:name</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>http://schemas.android.com/apk/res/android</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>name</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>style</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>^$</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>BY_NAME</order>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>http://schemas.android.com/apk/res/android</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>ANDROID_ATTRIBUTE_ORDER</order>
+            </rule>
+          </section>
+          <section>
+            <rule>
+              <match>
+                <AND>
+                  <NAME>.*</NAME>
+                  <XML_ATTRIBUTE />
+                  <XML_NAMESPACE>.*</XML_NAMESPACE>
+                </AND>
+              </match>
+              <order>BY_NAME</order>
+            </rule>
+          </section>
+        </rules>
+      </arrangement>
+    </codeStyleSettings>
+    <codeStyleSettings language="kotlin">
+      <option name="CODE_STYLE_DEFAULTS" value="KOTLIN_OFFICIAL" />
+      <indentOptions>
+        <option name="INDENT_SIZE" value="2" />
+        <option name="CONTINUATION_INDENT_SIZE" value="2" />
+        <option name="TAB_SIZE" value="2" />
+      </indentOptions>
+    </codeStyleSettings>
+  </code_scheme>
+</component>
@@ -0,0 +1,6 @@
+<component name="ProjectCodeStyleConfiguration">
+  <state>
+    <option name="USE_PER_PROJECT_SETTINGS" value="true" />
+    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default (1)" />
+  </state>
+</component>
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="PROJECT" charset="UTF-8" />
+  </component>
+</project>
@@ -3,9 +3,11 @@ language: android
 android:
  components:
    - tools
-    - build-tools-23.0.2
-    - android-23
+    - build-tools-28.0.3
+    - android-28
    - extra-android-m2repository
+  licenses:
+    - '.+'

 script:
  - ./gradlew test
@@ -29,5 +31,5 @@ sudo: false

 env:
  global:
-    - secure: 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
-    - secure: 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
+    - secure: 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
+    - secure: 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
@@ -0,0 +1,70 @@
+# Community Contribution Guidelines
+
+As the creators and maintainers of this project, we want to ensure that the project lives and continues to grow. Not blocked by any singular person's computer time. One of the simplest ways of doing this is by encouraging a larger set of shallow contributors. Through this, we hope to mitigate the problems of a project that needs updates, but there is no-one who has the power to do so.
+
+#### Development Process
+
+We maintain two permanent, protected branches: `master` and `development`.
+
+`master` is for the current release. It has already been distributed to jcenter and can't be modified at this point (except for docs that may be incorrect for the current release!).
+
+`development` is where we stage work for the *next* release. Pull requests should be directed to this branch.
+
+When working on a new feature or fix that may span multiple commits, please do so in a feature branch (ex: `feature/my_cool_thing`). Please clean up these feature branches once merged into `development`.
+
+When a new version is ready to be released, please create a pull request to merge `development` into `master`, named something like "Release 10.0". Then we can have some final discussion before we merge it into `master` and push the release out to the public.
+
+Since `development` is a *shared* branch, it is important not to ever rebase this branch onto `master`. If a bug fix is applied to `master` it can be merged into `development` using good old simple `git checkout development && git merge master`. Yes this will clutter the history a little bit, but it also provides important context to know how/when a patch was applied. Merge commits can be considered necessary historical data, not warts on an idealized history graph.
+
+#### Testing
+
+To run tests locally, just run `./gradlew test`. Tests should always be run before pushing anything to the repo.
+
+#### Ownership
+
+If you get a merged pull-request of substance (ie not just a typo fix), then you are eligible for push access to this repo. Simply request access via a new GitHub issue.
+
+Offhand, it is easy to imagine that this would make code quality suffer, but in reality it offers fresh perspectives to the codebase and encourages ownership from people who are depending on the project. If you are building a project that relies on this codebase, then you probably have the skills to improve it and offer valuable feedback. At the end of the day, there isn't too much risk in this, as the `master` branch is still locked, and jcenter access is still being restricted.
+
+Everyone comes in with their own perspective on what a project could/should look like, and encouraging discussion can help expose good ideas sooner.
+
+#### Why do we give out push access?
+
+It can be overwhelming to be offered the chance to wipe the source code for a project. Do not worry, we do not let you push to master. All code is peer-reviewed, and we have the convention that someone other than the submitter should merge non-trivial pull requests.
+
+As a contributor, you can merge other people's pull requests, or other contributors can merge yours. You will not be assigned a pull request, but you are welcome to jump in and take a code review on topics that interest you.
+
+This project is not continuously deployed, there is space for debate after review too. Offering everyone the chance to revert, or make an amending pull request. If it feels right, merge.
+
+#### How can we help you get comfortable contributing?
+
+It is normal for a first pull request to be a potential fix for a problem, and moving on from there to helping the project's direction can be difficult. We will try to help contributors cross that barrier by offering good first step issues. These issues can be fixed without feeling like you are stepping on toes. Ideally, these are non-critical issues that are well defined. They will be purposely avoided by mature contributors to the project, to make space for others.
+
+We aim to keep all project discussion inside GitHub issues. This is to make sure valuable discussion is accessible via search. If you have questions about how to use the library, or how the project is running - GitHub issues are the goto tool for this project.
+
+#### Our expectations on you as a contributor
+
+To quote [@alloy](https://github.com/alloy) from [this issue](https://github.com/Moya/Moya/issues/135):
+
+> Do not ever feel bad for not contributing to open source.
+
+We want contributors to provide ideas, keep the ship shipping and to take some of the load from others. It is non-obligatory; we’re here to get things done in an enjoyable way. :trophy:
+
+The fact that you will have push access will allow you to:
+
+- Avoid having to fork the project if you want to submit other pull requests, as you will be able to create branches directly on the project.
+- Help triage issues and merge pull requests.
+- Pick up the project if other maintainers move their focus elsewhere.
+
+It is up to you to use those superpowers or not though 😉
+
+If someone submits a pull request that is not perfect, and you are reviewing, it is better to think about the PR's motivation rather than the specific implementation. Having braces on the wrong line should not be a blocker. Though we do want to keep test coverage high, we will work with you to figure that out together.
+
+#### What about if you have problems that cannot be discussed in a public issue?
+
+[Eric Kuck](https://github.com/erickuck) has a contactable email on his GitHub profile, and is happy to talk about any problems.
+
+#### This is a different way to handle open source! Where did it come from?
+
+The original source of this document can be found at [https://github.com/moya/contributors](https://github.com/moya/contributors).
+
@@ -1,11 +1,11 @@
-[![Travis Build](https://travis-ci.org/bluelinelabs/Conductor.svg)](https://travis-ci.org/bluelinelabs/Conductor) [![Android Arsenal](https://img.shields.io/badge/Android%20Arsenal-Conductor-brightgreen.svg?style=flat)](http://android-arsenal.com/details/1/3361) [![Javadocs](http://javadoc.io/badge/com.bluelinelabs/conductor.svg)](http://javadoc.io/doc/com.bluelinelabs/conductor)
+[![Travis Build](https://travis-ci.com/bluelinelabs/Conductor.svg)](https://travis-ci.com/bluelinelabs/Conductor) [![Android Arsenal](https://img.shields.io/badge/Android%20Arsenal-Conductor-brightgreen.svg?style=flat)](http://android-arsenal.com/details/1/3361) [![Javadocs](http://javadoc.io/badge/com.bluelinelabs/conductor.svg)](http://javadoc.io/doc/com.bluelinelabs/conductor)

 # Conductor

 A small, yet full-featured framework that allows building View-based Android applications. Conductor provides a light-weight wrapper around standard Android Views that does just about everything you'd want:

-              |  Conductor
------|------------------------------
+|           |  Conductor  |
+|-----------|-------------|
 :tada: | Easy integration
 :point_up: | Single Activity apps without using Fragments
 :recycle: | Simple but powerful lifecycle management
@@ -13,50 +13,51 @@ A small, yet full-featured framework that allows building View-based Android app
 :twisted_rightwards_arrows: | Beautiful transitions between views
 :floppy_disk: | State persistence
 :phone: | Callbacks for onActivityResult, onRequestPermissionsResult, etc
-:european_post_office: | MVP / MVVM / VIPER / MVC ready
+:european_post_office: | MVP / MVVM / MVI / VIPER / MVC ready

 Conductor is architecture-agnostic and does not try to force any design decisions on the developer. We here at BlueLine Labs tend to use either MVP or MVVM, but it would work equally well with standard MVC or whatever else you want to throw at it.

 ## Installation

 ```gradle
-compile 'com.bluelinelabs:conductor:2.0.3'
+implementation 'com.bluelinelabs:conductor:3.0.0-rc5'

-// If you want the components that go along with
-// Android's support libraries (currently just a PagerAdapter):
-compile 'com.bluelinelabs:conductor-support:2.0.3'
+// AndroidX Transition change handlers:
+implementation 'com.bluelinelabs:conductor-androidx-transition:3.0.0-rc5'

-// If you want RxJava/RxAndroid lifecycle support:
-compile 'com.bluelinelabs:conductor-rxlifecycle:2.0.3'
+// ViewPager PagerAdapter:
+implementation 'com.bluelinelabs:conductor-viewpager:3.0.0-rc5'
+
+// RxJava2 lifecycle support:
+implementation 'com.bluelinelabs:conductor-rxlifecycle2:3.0.0-rc5'
+
+// RxJava2 Autodispose support:
+implementation 'com.bluelinelabs:conductor-autodispose:3.0.0-rc5'
+
+// Lifecycle-aware Controllers (architecture components):
+implementation 'com.bluelinelabs:conductor-archlifecycle:3.0.0-rc5'
 ```

-SNAPSHOT:
+**SNAPSHOT**

-```gradle
-compile 'com.bluelinelabs:conductor:2.0.4-SNAPSHOT'
-compile 'com.bluelinelabs:conductor-support:2.0.4-SNAPSHOT'
-compile 'com.bluelinelabs:conductor-rxlifecycle:2.0.4-SNAPSHOT'
-```
-
-You also have to add the url to the snapshot repository:
+Just use `3.0.1-SNAPSHOT` as your version number in any of the dependencies above and add the url to the snapshot repository:

 ```gradle
 allprojects {
  repositories {
-    ...
-
    maven { url "https://oss.sonatype.org/content/repositories/snapshots/" }
+  }
 }
 ```

 ## Components to Know

-              |  Conductor Components
+|             |  Conductor Components |
 ------|------------------------------
 __Controller__ | The Controller is the View wrapper that will give you all of your lifecycle management features. Think of it as a lighter-weight and more predictable Fragment alternative with an easier to manage lifecycle.
 __Router__ | A Router implements navigation and backstack handling for Controllers. Router objects are attached to Activity/containing ViewGroup pairs. Routers do not directly render or push Views to the container ViewGroup, but instead defer this responsibility to the ControllerChangeHandler specified in a given transaction.
 __ControllerChangeHandler__ | ControllerChangeHandlers are responsible for swapping the View for one Controller to the View of another. They can be useful for performing animations and transitions between Controllers. Several default ControllerChangeHandlers are included.
-__ControllerTransaction__ | Transactions are used to define data about adding Controllers. RouterControllerTransactions are used to push a Controller to a Router with specified ControllerChangeHandlers, while ChildControllerTransactions are used to add child Controllers.
+__RouterTransaction__ | Transactions are used to define data about adding Controllers. RouterTransactions are used to push a Controller to a Router with specified ControllerChangeHandlers, while ChildControllerTransactions are used to add child Controllers.

 ## Getting Started

@@ -73,7 +74,7 @@ public class MainActivity extends Activity {

        setContentView(R.layout.activity_main);

-        ViewGroup container = (ViewGroup)findViewById(R.id.controller_container);
+        ViewGroup container = (ViewGroup) findViewById(R.id.controller_container);

        router = Conductor.attachRouter(this, container, savedInstanceState);
        if (!router.hasRootController()) {
@@ -97,9 +98,9 @@ public class MainActivity extends Activity {
 public class HomeController extends Controller {

    @Override
-    protected View onCreateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container) {
+    protected View onCreateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container, @Nullable Bundle savedViewState) {
        View view = inflater.inflate(R.layout.controller_home, container, false);
-        ((TextView)view.findViewById(R.id.tv_title)).setText("Hello World");
+        ((TextView) view.findViewById(R.id.tv_title)).setText("Hello World");
        return view;
    }

@@ -114,7 +115,7 @@ public class HomeController extends Controller {

 The lifecycle of a Controller is significantly simpler to understand than that of a Fragment. A lifecycle diagram is shown below:

-![Controller Lifecycle](docs/Controller Lifecycle.jpg)
+![Controller Lifecycle](docs/Controller%20Lifecycle.jpg)

 ## Advanced Topics

@@ -128,11 +129,19 @@ The lifecycle of a Controller is significantly simpler to understand than that o
 `getChildRouter` can be called on a `Controller` in order to get a nested `Router` into which child `Controller`s can be pushed. This enables creating advanced layouts, such as Master/Detail.

 ### RxJava Lifecycle
-If the RxLifecycle dependency has been added, there is an `RxController` available that can be used along with the standard [RxLifecycle library](https://github.com/trello/RxLifecycle). There is also a `ControllerLifecycleProvider` available if you do not wish to use this subclass.
+If the AutoDispose dependency has been added, there is a `ControllerScopeProvider` available that can be used along with the standard [AutoDispose library](https://github.com/uber/AutoDispose).
+
+## Community Projects
+The community has provided several helpful modules to make developing apps with Conductor even easier. Here's a collection of helpful libraries:
+
+* [ConductorGlide](https://github.com/MkhytarMkhoian/ConductorGlide) - Adds Glide lifecycle support to Controllers
+* [ConductorDialog](https://github.com/MkhytarMkhoian/ConductorDialog) - Adds a helpful DialogController (a Conductor version of DialogFragment)
+* [Mosby-Conductor](https://github.com/sockeqwe/mosby-conductor) - A plugin to integrate Mosby, an MVP/MVI library
+

 ## License
 ```
-Copyright 2016 BlueLine Labs, Inc.
+Copyright 2020 BlueLine Labs, Inc.

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -1,21 +1,41 @@
 buildscript {
+    apply from: rootProject.file('dependencies.gradle')
+
    repositories {
        jcenter()
+        google()
    }
    dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.0'
+        classpath 'com.android.tools.build:gradle:3.6.3'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlinVersion"
+        classpath "com.vanniktech:gradle-maven-publish-plugin:$mvnPublishVersion"
    }
 }

 allprojects {
    repositories {
+        mavenCentral()
+        maven { url 'https://maven.google.com' }
        jcenter()
-        mavenLocal()
+    }
+
+    plugins.withType(com.android.build.gradle.BasePlugin).configureEach { plugin ->
+        plugin.extension.compileOptions {
+            sourceCompatibility = JavaVersion.VERSION_1_8
+            targetCompatibility = JavaVersion.VERSION_1_8
+        }
+    }
+
+    tasks.withType(JavaCompile).configureEach { task ->
+        task.sourceCompatibility = JavaVersion.VERSION_1_8
+        task.targetCompatibility = JavaVersion.VERSION_1_8
+    }
+
+    tasks.withType(org.jetbrains.kotlin.gradle.dsl.KotlinJvmCompile).configureEach { task ->
+        task.kotlinOptions {
+            jvmTarget = "1.8"
+        }
    }
 }

-task wrapper(type: Wrapper) {
-    gradleVersion = '2.10'
-}
-
 apply from: rootProject.file('dependencies.gradle')
@@ -1,19 +1,20 @@
-apply plugin: 'java'
+apply plugin: 'java-library'

 configurations {
    lintChecks
 }

 dependencies {
-    compile rootProject.ext.lintapi
-    compile rootProject.ext.lintchecks
+    compileOnly rootProject.ext.lintapi
+    compileOnly rootProject.ext.lintchecks

-    lintChecks files(jar)
+    testImplementation rootProject.ext.lint
+    testImplementation rootProject.ext.lintTests
 }

 jar {
    manifest {
-        attributes('Lint-Registry': 'com.bluelinelabs.conductor.lint.IssueRegistry')
+        attributes('Lint-Registry-v2': 'com.bluelinelabs.conductor.lint.IssueRegistry')
    }
 }

@@ -1,7 +1,7 @@
 package com.bluelinelabs.conductor.lint;

-import com.android.annotations.NonNull;
-import com.android.tools.lint.client.api.JavaParser.ResolvedClass;
+import com.android.tools.lint.client.api.JavaEvaluator;
+import com.android.tools.lint.client.api.UElementHandler;
 import com.android.tools.lint.detector.api.Category;
 import com.android.tools.lint.detector.api.Detector;
 import com.android.tools.lint.detector.api.Implementation;
@@ -9,92 +9,87 @@ import com.android.tools.lint.detector.api.Issue;
 import com.android.tools.lint.detector.api.JavaContext;
 import com.android.tools.lint.detector.api.Scope;
 import com.android.tools.lint.detector.api.Severity;
-import com.android.tools.lint.detector.api.Speed;

-import java.lang.reflect.Modifier;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.uast.UClass;
+import org.jetbrains.uast.UElement;
+import org.jetbrains.uast.UMethod;
+import org.jetbrains.uast.UTypeReferenceExpression;
+
 import java.util.Collections;
 import java.util.List;

-import lombok.ast.ClassDeclaration;
-import lombok.ast.ConstructorDeclaration;
-import lombok.ast.Node;
-import lombok.ast.NormalTypeBody;
-import lombok.ast.StrictListAccessor;
-import lombok.ast.TypeMember;
-import lombok.ast.VariableDefinition;
+@SuppressWarnings("UnstableApiUsage")
+public final class ControllerChangeHandlerIssueDetector extends Detector implements Detector.UastScanner {

-public final class ControllerChangeHandlerIssueDetector extends Detector implements Detector.JavaScanner, Detector.ClassScanner {
-
-    public static final Issue ISSUE =
+    static final Issue ISSUE =
            Issue.create("ValidControllerChangeHandler", "ControllerChangeHandler not instantiatable",
                    "Non-abstract ControllerChangeHandler instances must have a default constructor for the"
                            + " system to re-create them in the case of the process being killed.",
                    Category.CORRECTNESS, 6, Severity.FATAL,
                    new Implementation(ControllerChangeHandlerIssueDetector.class, Scope.JAVA_FILE_SCOPE));

-    public ControllerChangeHandlerIssueDetector() { }
+    private static final String CLASS_NAME = "com.bluelinelabs.conductor.ControllerChangeHandler";

-    @NonNull
    @Override
-    public Speed getSpeed() {
-        return Speed.FAST;
+    public List<Class<? extends UElement>> getApplicableUastTypes() {
+        return Collections.<Class<? extends UElement>>singletonList(UClass.class);
    }

    @Override
-    public List<String> applicableSuperClasses() {
-        return Collections.singletonList("com.bluelinelabs.conductor.ControllerChangeHandler");
-    }
+    public UElementHandler createUastHandler(final JavaContext context) {
+        final JavaEvaluator evaluator = context.getEvaluator();

-    @Override
-    public void checkClass(@NonNull JavaContext context, ClassDeclaration node,
-                           @NonNull Node declarationOrAnonymous, @NonNull ResolvedClass cls) {
+        return new UElementHandler() {

-        if (node == null) {
-            return;
-        }
+            @Override
+            public void visitClass(@NotNull UClass node) {
+                if (evaluator.isAbstract(node)) {
+                    return;
+                }

-        final int flags = node.astModifiers().getEffectiveModifierFlags();
-        if ((flags & Modifier.ABSTRACT) != 0) {
-            return;
-        }
+                boolean hasSuperType = false;
+                for (UTypeReferenceExpression superType : node.getUastSuperTypes()) {
+                    if (CLASS_NAME.equals(superType.asRenderString())) {
+                        hasSuperType = true;
+                        break;
+                    }
+                }
+                if (!hasSuperType) {
+                    return;
+                }

-        if ((flags & Modifier.PUBLIC) == 0) {
-            String message = String.format("This ControllerChangeHandler class should be public (%1$s)", cls.getName());
-            context.report(ISSUE, node, context.getLocation(node.astName()), message);
-            return;
-        }
+                if (!evaluator.isPublic(node)) {
+                    String message = String.format("This ControllerChangeHandler class should be public (%1$s)", node.getQualifiedName());
+                    context.report(ISSUE, node, context.getLocation((UElement) node), message);
+                    return;
+                }

-        if (cls.getContainingClass() != null && (flags & Modifier.STATIC) == 0) {
-            String message = String.format("This ControllerChangeHandler inner class should be static (%1$s)", cls.getName());
-            context.report(ISSUE, node, context.getLocation(node.astName()), message);
-            return;
-        }
+                if (node.getContainingClass() != null && !evaluator.isStatic(node)) {
+                    String message = String.format("This ControllerChangeHandler inner class should be static (%1$s)", node.getQualifiedName());
+                    context.report(ISSUE, node, context.getLocation((UElement) node), message);
+                    return;
+                }

-        boolean hasConstructor = false;
-        boolean hasDefaultConstructor = false;
-        NormalTypeBody body = node.astBody();
-        if (body != null) {
-            for (TypeMember member : body.astMembers()) {
-                if (member instanceof ConstructorDeclaration) {
-                    hasConstructor = true;
-                    ConstructorDeclaration constructor = (ConstructorDeclaration)member;
-
-                    if (constructor.astModifiers().isPublic()) {
-                        StrictListAccessor<VariableDefinition, ConstructorDeclaration> params = constructor.astParameters();
-                        if (params.isEmpty()) {
+                boolean hasConstructor = false;
+                boolean hasDefaultConstructor = false;
+                for (UMethod method : node.getMethods()) {
+                    if (method.isConstructor()) {
+                        hasConstructor = true;
+                        if (evaluator.isPublic(method) && method.getUastParameters().size() == 0) {
                            hasDefaultConstructor = true;
                            break;
                        }
                    }
                }
-            }
-        }

-        if (hasConstructor && !hasDefaultConstructor) {
-            String message = String.format(
-                    "This ControllerChangeHandler needs to have a public default constructor (`%1$s`)",
-                    cls.getName());
-            context.report(ISSUE, node, context.getLocation(node.astName()), message);
-        }
+                if (hasConstructor && !hasDefaultConstructor) {
+                    String message = String.format(
+                            "This ControllerChangeHandler needs to have a public default constructor (`%1$s`)", node.getQualifiedName());
+                    context.report(ISSUE, node, context.getLocation((UElement) node), message);
+                }
+            }
+        };
    }
-}
+
+}
@@ -1,8 +1,8 @@
 package com.bluelinelabs.conductor.lint;

 import com.android.SdkConstants;
-import com.android.annotations.NonNull;
-import com.android.tools.lint.client.api.JavaParser.ResolvedClass;
+import com.android.tools.lint.client.api.JavaEvaluator;
+import com.android.tools.lint.client.api.UElementHandler;
 import com.android.tools.lint.detector.api.Category;
 import com.android.tools.lint.detector.api.Detector;
 import com.android.tools.lint.detector.api.Implementation;
@@ -10,99 +10,97 @@ import com.android.tools.lint.detector.api.Issue;
 import com.android.tools.lint.detector.api.JavaContext;
 import com.android.tools.lint.detector.api.Scope;
 import com.android.tools.lint.detector.api.Severity;
-import com.android.tools.lint.detector.api.Speed;

-import java.lang.reflect.Modifier;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.uast.UClass;
+import org.jetbrains.uast.UElement;
+import org.jetbrains.uast.UMethod;
+import org.jetbrains.uast.UParameter;
+import org.jetbrains.uast.UTypeReferenceExpression;
+
 import java.util.Collections;
 import java.util.List;

-import lombok.ast.ClassDeclaration;
-import lombok.ast.ConstructorDeclaration;
-import lombok.ast.Node;
-import lombok.ast.NormalTypeBody;
-import lombok.ast.StrictListAccessor;
-import lombok.ast.TypeMember;
-import lombok.ast.VariableDefinition;
+@SuppressWarnings("UnstableApiUsage")
+public final class ControllerIssueDetector extends Detector implements Detector.UastScanner {

-public final class ControllerIssueDetector extends Detector implements Detector.JavaScanner, Detector.ClassScanner {
-
-    public static final Issue ISSUE =
+    static final Issue ISSUE =
            Issue.create("ValidController", "Controller not instantiatable",
                    "Non-abstract Controller instances must have a default or single-argument constructor"
                            + " that takes a Bundle in order for the system to re-create them in the"
                            + " case of the process being killed.", Category.CORRECTNESS, 6, Severity.FATAL,
                    new Implementation(ControllerIssueDetector.class, Scope.JAVA_FILE_SCOPE));

-    public ControllerIssueDetector() { }
+    private static final String CLASS_NAME = "com.bluelinelabs.conductor.Controller";

-    @NonNull
    @Override
-    public Speed getSpeed() {
-        return Speed.FAST;
+    public List<Class<? extends UElement>> getApplicableUastTypes() {
+        return Collections.<Class<? extends UElement>>singletonList(UClass.class);
    }

    @Override
-    public List<String> applicableSuperClasses() {
-        return Collections.singletonList("com.bluelinelabs.conductor.Controller");
-    }
+    public UElementHandler createUastHandler(final JavaContext context) {
+        final JavaEvaluator evaluator = context.getEvaluator();

-    @Override
-    public void checkClass(@NonNull JavaContext context, ClassDeclaration node,
-                           @NonNull Node declarationOrAnonymous, @NonNull ResolvedClass cls) {
+        return new UElementHandler() {
+            @Override
+            public void visitClass(@NotNull UClass node) {
+                if (evaluator.isAbstract(node)) {
+                    return;
+                }

-        if (node == null) {
-            return;
-        }
+                boolean hasSuperType = false;
+                for (UTypeReferenceExpression superType : node.getUastSuperTypes()) {
+                    if (CLASS_NAME.equals(superType.asRenderString())) {
+                        hasSuperType = true;
+                        break;
+                    }
+                }
+                if (!hasSuperType) {
+                    return;
+                }

-        final int flags = node.astModifiers().getEffectiveModifierFlags();
-        if ((flags & Modifier.ABSTRACT) != 0) {
-            return;
-        }
+                if (!evaluator.isPublic(node)) {
+                    String message = String.format("This Controller class should be public (%1$s)", node.getQualifiedName());
+                    context.report(ISSUE, node, context.getLocation((UElement) node), message);
+                    return;
+                }

-        if ((flags & Modifier.PUBLIC) == 0) {
-            String message = String.format("This Controller class should be public (%1$s)", cls.getName());
-            context.report(ISSUE, node, context.getLocation(node.astName()), message);
-            return;
-        }
+                if (node.getContainingClass() != null && !evaluator.isStatic(node)) {
+                    String message = String.format("This Controller inner class should be static (%1$s)", node.getQualifiedName());
+                    context.report(ISSUE, node, context.getLocation((UElement) node), message);
+                    return;
+                }

-        if (cls.getContainingClass() != null && (flags & Modifier.STATIC) == 0) {
-            String message = String.format("This Controller inner class should be static (%1$s)", cls.getName());
-            context.report(ISSUE, node, context.getLocation(node.astName()), message);
-            return;
-        }
-
-        boolean hasConstructor = false;
-        boolean hasDefaultConstructor = false;
-        boolean hasBundleConstructor = false;
-        NormalTypeBody body = node.astBody();
-        if (body != null) {
-            for (TypeMember member : body.astMembers()) {
-                if (member instanceof ConstructorDeclaration) {
-                    hasConstructor = true;
-                    ConstructorDeclaration constructor = (ConstructorDeclaration)member;
-
-                    if (constructor.astModifiers().isPublic()) {
-                        StrictListAccessor<VariableDefinition, ConstructorDeclaration> params = constructor.astParameters();
-                        if (params.isEmpty()) {
-                            hasDefaultConstructor = true;
-                            break;
-                        } else if (params.size() == 1 &&
-                                (params.first().astTypeReference().getTypeName().equals(SdkConstants.CLASS_BUNDLE)) ||
-                                params.first().astTypeReference().getTypeName().equals("Bundle")) {
-                            hasBundleConstructor = true;
-                            break;
+                boolean hasConstructor = false;
+                boolean hasDefaultConstructor = false;
+                boolean hasBundleConstructor = false;
+                for (UMethod method : node.getMethods()) {
+                    if (method.isConstructor()) {
+                        hasConstructor = true;
+                        if (evaluator.isPublic(method)) {
+                            List<UParameter> parameters = method.getUastParameters();
+                            if (parameters.size() == 0) {
+                                hasDefaultConstructor = true;
+                                break;
+                            } else if (parameters.size() == 1 &&
+                                    (parameters.get(0).getType().equalsToText(SdkConstants.CLASS_BUNDLE)) ||
+                                    parameters.get(0).getType().equalsToText("Bundle")) {
+                                hasBundleConstructor = true;
+                            }
                        }
                    }
                }
-            }
-        }

-        if (hasConstructor && !hasDefaultConstructor && !hasBundleConstructor) {
-            String message = String.format(
-                    "This Controller needs to have either a public default constructor or a" +
-                            " public single-argument constructor that takes a Bundle. (`%1$s`)",
-                    cls.getName());
-            context.report(ISSUE, node, context.getLocation(node.astName()), message);
-        }
+                if (hasConstructor && !hasDefaultConstructor && !hasBundleConstructor) {
+                    String message = String.format(
+                            "This Controller needs to have either a public default constructor or a" +
+                                    " public single-argument constructor that takes a Bundle. (`%1$s`)",
+                            node.getQualifiedName());
+                    context.report(ISSUE, node, context.getLocation((UElement) node), message);
+                }
+            }
+        };
    }
-}
+
+}
@@ -5,10 +5,21 @@ import com.android.tools.lint.detector.api.Issue;
 import java.util.Arrays;
 import java.util.List;

+import static com.android.tools.lint.detector.api.ApiKt.CURRENT_API;
+
+@SuppressWarnings({"unused", "UnstableApiUsage"})
 public final class IssueRegistry extends com.android.tools.lint.client.api.IssueRegistry {
-    @Override public List<Issue> getIssues() {
+
+    @Override
+    public List<Issue> getIssues() {
        return Arrays.asList(
                ControllerIssueDetector.ISSUE,
-                ControllerChangeHandlerIssueDetector.ISSUE);
+                ControllerChangeHandlerIssueDetector.ISSUE
+        );
    }
-}
+
+    @Override
+    public int getApi() {
+        return CURRENT_API;
+    }
+}
@@ -0,0 +1,112 @@
+package com.bluelinelabs.conductor.lint;
+
+import org.intellij.lang.annotations.Language;
+import org.junit.Test;
+
+import static com.android.tools.lint.checks.infrastructure.TestFiles.java;
+import static com.android.tools.lint.checks.infrastructure.TestLintTask.lint;
+
+public class ControllerChangeHandlerDetectorTest {
+
+    private static final String CONSTRUCTOR =
+            "src/test/SampleHandler.java:2: Error: This ControllerChangeHandler needs to have a public default constructor (test.SampleHandler) [ValidControllerChangeHandler]\n"
+            + "public class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+            + "^\n"
+            + "1 errors, 0 warnings\n";
+    private static final String PRIVATE_CLASS_ERROR =
+            "src/test/SampleHandler.java:2: Error: This ControllerChangeHandler class should be public (test.SampleHandler) [ValidControllerChangeHandler]\n"
+                    + "private class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                    + "^\n"
+                    + "1 errors, 0 warnings\n";
+
+    @Test
+    public void testWithNoConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expectClean();
+    }
+
+    @Test
+    public void testWithEmptyConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                + "    public SampleHandler() { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expectClean();
+    }
+
+    @Test
+    public void testWithInvalidConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                + "    public SampleHandler(int number) { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expect(CONSTRUCTOR);
+    }
+
+    @Test
+    public void testWithEmptyAndInvalidConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                + "    public SampleHandler() { }\n"
+                + "    public SampleHandler(int number) { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expectClean();
+    }
+
+    @Test
+    public void testWithPrivateConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                + "    private SampleHandler() { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expect(CONSTRUCTOR);
+    }
+
+    @Test
+    public void testWithPrivateClass() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "private class SampleHandler extends com.bluelinelabs.conductor.ControllerChangeHandler {\n"
+                + "    public SampleHandler() { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expect(PRIVATE_CLASS_ERROR);
+    }
+
+}
@@ -0,0 +1,112 @@
+package com.bluelinelabs.conductor.lint;
+
+import org.intellij.lang.annotations.Language;
+import org.junit.Test;
+
+import static com.android.tools.lint.checks.infrastructure.TestFiles.java;
+import static com.android.tools.lint.checks.infrastructure.TestLintTask.lint;
+
+public class ControllerDetectorTest {
+
+    private static final String CONSTRUCTOR_ERROR =
+            "src/test/SampleController.java:2: Error: This Controller needs to have either a public default constructor or a public single-argument constructor that takes a Bundle. (test.SampleController) [ValidController]\n"
+            + "public class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+            + "^\n"
+            + "1 errors, 0 warnings\n";
+    private static final String CLASS_ERROR =
+            "src/test/SampleController.java:2: Error: This Controller class should be public (test.SampleController) [ValidController]\n"
+                    + "private class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                    + "^\n"
+                    + "1 errors, 0 warnings\n";
+
+    @Test
+    public void testWithNoConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expectClean();
+    }
+
+    @Test
+    public void testWithEmptyConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                + "    public SampleController() { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expectClean();
+    }
+
+    @Test
+    public void testWithInvalidConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                + "    public SampleController(int number) { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expect(CONSTRUCTOR_ERROR);
+    }
+
+    @Test
+    public void testWithEmptyAndInvalidConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                + "    public SampleController() { }\n"
+                + "    public SampleController(int number) { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expectClean();
+    }
+
+    @Test
+    public void testWithPrivateConstructor() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "public class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                + "    private SampleController() { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expect(CONSTRUCTOR_ERROR);
+    }
+
+    @Test
+    public void testWithPrivateClass() {
+        @Language("JAVA") String source = ""
+                + "package test;\n"
+                + "private class SampleController extends com.bluelinelabs.conductor.Controller {\n"
+                + "    public SampleController() { }\n"
+                + "}";
+
+        lint()
+                .files(java(source))
+                .issues(ControllerIssueDetector.ISSUE, ControllerChangeHandlerIssueDetector.ISSUE)
+                .run()
+                .expect(CLASS_ERROR);
+    }
+
+}
@@ -1,20 +1,7 @@
-apply from: rootProject.file('dependencies.gradle')
-apply from: rootProject.file('gradle-mvn-push.gradle')
-
 apply plugin: 'com.android.library'

 android {
    compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
-
-    lintOptions {
-        abortOnError false
-    }
-
-    compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_7
-        targetCompatibility JavaVersion.VERSION_1_7
-    }

    defaultConfig {
        minSdkVersion rootProject.ext.minSdkVersion
@@ -25,9 +12,12 @@ android {
 }

 dependencies {
-    compile rootProject.ext.supportAppCompat
-    compile project(':conductor')
+    api rootProject.ext.archComponentsLifecycle
+
+    implementation project(':conductor')
 }

-ext.artifactId = 'conductor-support'
+ext.artifactId = 'conductor-arch-components-lifecycle'

+apply from: rootProject.file('dependencies.gradle')
+apply plugin: "com.vanniktech.maven.publish"
@@ -0,0 +1,3 @@
+POM_NAME=Conductor Architecture Components Lifecycle Extensions
+POM_ARTIFACT_ID=conductor-archlifecycle
+POM_PACKAGING=aar
@@ -0,0 +1,3 @@
+<manifest package="com.bluelinelabs.conductor.archlifecycle">
+    <application />
+</manifest>
@@ -0,0 +1,65 @@
+package com.bluelinelabs.conductor.archlifecycle;
+
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.Lifecycle.Event;
+import androidx.lifecycle.LifecycleOwner;
+import androidx.lifecycle.LifecycleRegistry;
+import android.content.Context;
+import androidx.annotation.NonNull;
+import android.view.View;
+
+import com.bluelinelabs.conductor.Controller;
+import com.bluelinelabs.conductor.Controller.LifecycleListener;
+
+public class ControllerLifecycleOwner implements LifecycleOwner {
+
+    private final LifecycleRegistry lifecycleRegistry;
+
+    public <T extends Controller & LifecycleOwner> ControllerLifecycleOwner(@NonNull T lifecycleController) {
+        lifecycleRegistry = new LifecycleRegistry(lifecycleController); // --> State.INITIALIZED
+
+        lifecycleController.addLifecycleListener(new LifecycleListener() {
+            @Override
+            public void postContextAvailable(@NonNull Controller controller, @NonNull Context context) {
+                lifecycleRegistry.handleLifecycleEvent(Event.ON_CREATE); // --> State.CREATED;
+            }
+
+            @Override
+            public void postCreateView(@NonNull Controller controller, @NonNull View view) {
+                lifecycleRegistry.handleLifecycleEvent(Event.ON_START); // --> State.STARTED;
+            }
+
+            @Override
+            public void postAttach(@NonNull Controller controller, @NonNull View view) {
+                lifecycleRegistry.handleLifecycleEvent(Event.ON_RESUME); // --> State.RESUMED;
+            }
+
+            @Override
+            public void preDetach(@NonNull Controller controller, @NonNull View view) {
+                lifecycleRegistry.handleLifecycleEvent(Event.ON_PAUSE); // --> State.STARTED;
+            }
+
+            @Override
+            public void preDestroyView(@NonNull Controller controller, @NonNull View view) {
+                lifecycleRegistry.handleLifecycleEvent(Event.ON_STOP); // --> State.CREATED;
+            }
+
+            @Override
+            public void preContextUnavailable(@NonNull Controller controller, @NonNull Context context) {
+                // do nothing
+            }
+
+            @Override
+            public void preDestroy(@NonNull Controller controller) {
+                lifecycleRegistry.handleLifecycleEvent(Event.ON_DESTROY); // --> State.DESTROYED;
+            }
+
+        });
+    }
+
+    @Override @NonNull
+    public Lifecycle getLifecycle() {
+        return lifecycleRegistry;
+    }
+
+}
@@ -0,0 +1,28 @@
+package com.bluelinelabs.conductor.archlifecycle;
+
+import androidx.lifecycle.Lifecycle;
+import androidx.lifecycle.LifecycleOwner;
+import android.os.Bundle;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import com.bluelinelabs.conductor.Controller;
+
+public abstract class LifecycleController extends Controller implements LifecycleOwner {
+
+    private final ControllerLifecycleOwner lifecycleOwner = new ControllerLifecycleOwner(this);
+
+    public LifecycleController() {
+        super();
+    }
+
+    public LifecycleController(@Nullable Bundle args) {
+        super(args);
+    }
+
+    @Override @NonNull
+    public Lifecycle getLifecycle() {
+        return lifecycleOwner.getLifecycle();
+    }
+
+}
@@ -0,0 +1,25 @@
+apply from: rootProject.file('dependencies.gradle')
+
+apply plugin: 'com.android.library'
+apply plugin: "com.vanniktech.maven.publish"
+
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode Integer.parseInt(project.VERSION_CODE)
+        versionName project.VERSION_NAME
+    }
+}
+
+dependencies {
+    api rootProject.ext.rxJava2
+    api rootProject.ext.autodispose
+    api rootProject.ext.autodisposeLifecycle
+
+    implementation project(':conductor')
+}
+
+ext.artifactId = 'conductor-autodispose'
@@ -0,0 +1,3 @@
+POM_NAME=Conductor AutoDispose Extensions
+POM_ARTIFACT_ID=conductor-autodispose
+POM_PACKAGING=aar
@@ -0,0 +1,3 @@
+<manifest package="com.bluelinelabs.conductor.autodispose">
+    <application />
+</manifest>
@@ -1,12 +1,14 @@
-package com.bluelinelabs.conductor.rxlifecycle;
+package com.bluelinelabs.conductor.autodispose;

 public enum ControllerEvent {

    CREATE,
+    CONTEXT_AVAILABLE,
    CREATE_VIEW,
    ATTACH,
    DETACH,
    DESTROY_VIEW,
+    CONTEXT_UNAVAILABLE,
    DESTROY

 }
@@ -0,0 +1,71 @@
+package com.bluelinelabs.conductor.autodispose;
+
+import android.content.Context;
+import androidx.annotation.NonNull;
+import android.view.View;
+
+import com.bluelinelabs.conductor.Controller;
+import com.uber.autodispose.OutsideScopeException;
+
+import io.reactivex.subjects.BehaviorSubject;
+
+public class ControllerLifecycleSubjectHelper {
+    private ControllerLifecycleSubjectHelper() { }
+
+    @NonNull
+    public static BehaviorSubject<ControllerEvent> create(@NonNull Controller controller) {
+        ControllerEvent initialState;
+        if (controller.isBeingDestroyed() || controller.isDestroyed()) {
+            throw new OutsideScopeException("Cannot bind to Controller lifecycle when outside of it.");
+        } else if (controller.isAttached()) {
+            initialState = ControllerEvent.ATTACH;
+        } else if (controller.getView() != null) {
+            initialState = ControllerEvent.CREATE_VIEW;
+        } else if (controller.getActivity() != null) {
+            initialState = ControllerEvent.CONTEXT_AVAILABLE;
+        } else {
+            initialState = ControllerEvent.CREATE;
+        }
+
+        final BehaviorSubject<ControllerEvent> subject = BehaviorSubject.createDefault(initialState);
+
+        controller.addLifecycleListener(new Controller.LifecycleListener() {
+            @Override
+            public void preContextAvailable(@NonNull Controller controller) {
+                subject.onNext(ControllerEvent.CONTEXT_AVAILABLE);
+            }
+
+            @Override
+            public void preCreateView(@NonNull Controller controller) {
+                subject.onNext(ControllerEvent.CREATE_VIEW);
+            }
+
+            @Override
+            public void preAttach(@NonNull Controller controller, @NonNull View view) {
+                subject.onNext(ControllerEvent.ATTACH);
+            }
+
+            @Override
+            public void preDetach(@NonNull Controller controller, @NonNull View view) {
+                subject.onNext(ControllerEvent.DETACH);
+            }
+
+            @Override
+            public void preDestroyView(@NonNull Controller controller, @NonNull View view) {
+                subject.onNext(ControllerEvent.DESTROY_VIEW);
+            }
+
+            @Override
+            public void preContextUnavailable(@NonNull Controller controller, @NonNull Context context) {
+                subject.onNext(ControllerEvent.CONTEXT_UNAVAILABLE);
+            }
+
+            @Override
+            public void preDestroy(@NonNull Controller controller) {
+                subject.onNext(ControllerEvent.DESTROY);
+            }
+        });
+
+        return subject;
+    }
+}
@@ -0,0 +1,81 @@
+package com.bluelinelabs.conductor.autodispose;
+
+import androidx.annotation.NonNull;
+
+import com.bluelinelabs.conductor.Controller;
+import com.uber.autodispose.OutsideScopeException;
+import com.uber.autodispose.lifecycle.LifecycleScopeProvider;
+import com.uber.autodispose.lifecycle.LifecycleScopes;
+import com.uber.autodispose.lifecycle.CorrespondingEventsFunction;
+
+import io.reactivex.CompletableSource;
+import io.reactivex.Observable;
+import io.reactivex.subjects.BehaviorSubject;
+
+public class ControllerScopeProvider implements LifecycleScopeProvider<ControllerEvent> {
+    private static final CorrespondingEventsFunction<ControllerEvent> CORRESPONDING_EVENTS =
+            new CorrespondingEventsFunction<ControllerEvent>() {
+                @Override
+                public ControllerEvent apply(ControllerEvent lastEvent) throws OutsideScopeException {
+                    switch (lastEvent) {
+                        case CREATE:
+                            return ControllerEvent.DESTROY;
+                        case CONTEXT_AVAILABLE:
+                            return ControllerEvent.CONTEXT_UNAVAILABLE;
+                        case CREATE_VIEW:
+                            return ControllerEvent.DESTROY_VIEW;
+                        case ATTACH:
+                            return ControllerEvent.DETACH;
+                        case DETACH:
+                            return ControllerEvent.DESTROY;
+                        default:
+                            throw new OutsideScopeException("Cannot bind to Controller lifecycle when outside of it.");
+                    }
+                }
+            };
+
+    @NonNull private final BehaviorSubject<ControllerEvent> lifecycleSubject;
+    @NonNull private final CorrespondingEventsFunction<ControllerEvent> correspondingEventsFunction;
+
+    public static ControllerScopeProvider from(@NonNull Controller controller) {
+        return new ControllerScopeProvider(controller, CORRESPONDING_EVENTS);
+    }
+
+    public static ControllerScopeProvider from(@NonNull Controller controller, @NonNull final ControllerEvent untilEvent) {
+        return new ControllerScopeProvider(controller, new CorrespondingEventsFunction<ControllerEvent>() {
+            @Override
+            public ControllerEvent apply(ControllerEvent controllerEvent) {
+                return untilEvent;
+            }
+        });
+    }
+
+    public static ControllerScopeProvider from(@NonNull Controller controller, @NonNull final CorrespondingEventsFunction<ControllerEvent> correspondingEventsFunction) {
+        return new ControllerScopeProvider(controller, correspondingEventsFunction);
+    }
+
+    private ControllerScopeProvider(@NonNull Controller controller, @NonNull CorrespondingEventsFunction<ControllerEvent> correspondingEventsFunction) {
+        lifecycleSubject = ControllerLifecycleSubjectHelper.create(controller);
+        this.correspondingEventsFunction = correspondingEventsFunction;
+    }
+
+    @Override
+    public Observable<ControllerEvent> lifecycle() {
+        return lifecycleSubject.hide();
+    }
+
+    @Override
+    public CorrespondingEventsFunction<ControllerEvent> correspondingEvents() {
+        return correspondingEventsFunction;
+    }
+
+    @Override
+    public ControllerEvent peekLifecycle() {
+        return lifecycleSubject.getValue();
+    }
+
+    @Override
+    public CompletableSource requestScope() throws Exception {
+        return LifecycleScopes.resolveScopeFromLifecycle(this);
+    }
+}
@@ -0,0 +1,25 @@
+apply from: rootProject.file('dependencies.gradle')
+
+apply plugin: 'com.android.library'
+apply plugin: "com.vanniktech.maven.publish"
+
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode Integer.parseInt(project.VERSION_CODE)
+        versionName project.VERSION_NAME
+    }
+}
+
+dependencies {
+    api rootProject.ext.rxJava2
+    api rootProject.ext.rxLifecycle2
+    api rootProject.ext.rxLifecycleAndroid2
+
+    implementation project(':conductor')
+}
+
+ext.artifactId = 'conductor-rxlifecycle2'
@@ -0,0 +1,3 @@
+POM_NAME=Conductor RxLifecycle2 Extensions
+POM_ARTIFACT_ID=conductor-rxlifecycle2
+POM_PACKAGING=aar
@@ -0,0 +1,3 @@
+<manifest package="com.bluelinelabs.conductor.rxlifecycle2">
+    <application />
+</manifest>
@@ -0,0 +1,14 @@
+package com.bluelinelabs.conductor.rxlifecycle2;
+
+public enum ControllerEvent {
+
+    CREATE,
+    CONTEXT_AVAILABLE,
+    CREATE_VIEW,
+    ATTACH,
+    DETACH,
+    DESTROY_VIEW,
+    CONTEXT_UNAVAILABLE,
+    DESTROY
+
+}
@@ -0,0 +1,71 @@
+package com.bluelinelabs.conductor.rxlifecycle2;
+
+import android.content.Context;
+import androidx.annotation.NonNull;
+import android.view.View;
+
+import com.bluelinelabs.conductor.Controller;
+import com.trello.rxlifecycle2.OutsideLifecycleException;
+
+import io.reactivex.subjects.BehaviorSubject;
+
+public class ControllerLifecycleSubjectHelper {
+    private ControllerLifecycleSubjectHelper() {
+    }
+
+    public static BehaviorSubject<ControllerEvent> create(Controller controller) {
+        ControllerEvent initialState;
+        if (controller.isBeingDestroyed() || controller.isDestroyed()) {
+            throw new OutsideLifecycleException("Cannot bind to Controller lifecycle when outside of it.");
+        } else if (controller.isAttached()) {
+            initialState = ControllerEvent.ATTACH;
+        } else if (controller.getView() != null) {
+            initialState = ControllerEvent.CREATE_VIEW;
+        } else if (controller.getActivity() != null) {
+            initialState = ControllerEvent.CONTEXT_AVAILABLE;
+        } else {
+            initialState = ControllerEvent.CREATE;
+        }
+
+        final BehaviorSubject<ControllerEvent> subject = BehaviorSubject.createDefault(initialState);
+
+        controller.addLifecycleListener(new Controller.LifecycleListener() {
+            @Override
+            public void preContextAvailable(@NonNull Controller controller) {
+                subject.onNext(ControllerEvent.CONTEXT_AVAILABLE);
+            }
+
+            @Override
+            public void preCreateView(@NonNull Controller controller) {
+                subject.onNext(ControllerEvent.CREATE_VIEW);
+            }
+
+            @Override
+            public void preAttach(@NonNull Controller controller, @NonNull View view) {
+                subject.onNext(ControllerEvent.ATTACH);
+            }
+
+            @Override
+            public void preDetach(@NonNull Controller controller, @NonNull View view) {
+                subject.onNext(ControllerEvent.DETACH);
+            }
+
+            @Override
+            public void preDestroyView(@NonNull Controller controller, @NonNull View view) {
+                subject.onNext(ControllerEvent.DESTROY_VIEW);
+            }
+
+            @Override
+            public void preContextUnavailable(@NonNull Controller controller, @NonNull Context context) {
+                subject.onNext(ControllerEvent.CONTEXT_UNAVAILABLE);
+            }
+
+            @Override
+            public void preDestroy(@NonNull Controller controller) {
+                subject.onNext(ControllerEvent.DESTROY);
+            }
+        });
+
+        return subject;
+    }
+}
@@ -1,29 +1,27 @@
-package com.bluelinelabs.conductor.rxlifecycle;
+package com.bluelinelabs.conductor.rxlifecycle2;

 import android.os.Bundle;
-import android.support.annotation.CheckResult;
-import android.support.annotation.NonNull;
-
+import androidx.annotation.CheckResult;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import com.bluelinelabs.conductor.Controller;
-import com.trello.rxlifecycle.LifecycleProvider;
-import com.trello.rxlifecycle.LifecycleTransformer;
-import com.trello.rxlifecycle.RxLifecycle;
-
-import rx.Observable;
-import rx.subjects.BehaviorSubject;
+import com.trello.rxlifecycle2.LifecycleProvider;
+import com.trello.rxlifecycle2.LifecycleTransformer;
+import com.trello.rxlifecycle2.RxLifecycle;
+import io.reactivex.Observable;
+import io.reactivex.subjects.BehaviorSubject;

 /**
 * A base {@link Controller} that can be used to expose lifecycle events using RxJava
 */
 public abstract class RxController extends Controller implements LifecycleProvider<ControllerEvent> {
-
    private final BehaviorSubject<ControllerEvent> lifecycleSubject;

-    public RxController() {
+    public RxController(){
        this(null);
    }

-    public RxController(Bundle args) {
+    public RxController(@Nullable Bundle args) {
        super(args);
        lifecycleSubject = ControllerLifecycleSubjectHelper.create(this);
    }
@@ -32,7 +30,7 @@ public abstract class RxController extends Controller implements LifecycleProvid
    @NonNull
    @CheckResult
    public final Observable<ControllerEvent> lifecycle() {
-        return lifecycleSubject.asObservable();
+        return lifecycleSubject.hide();
    }

    @Override
@@ -48,5 +46,4 @@ public abstract class RxController extends Controller implements LifecycleProvid
    public final <T> LifecycleTransformer<T> bindToLifecycle() {
        return RxControllerLifecycle.bindController(lifecycleSubject);
    }
-
-}
+}
@@ -0,0 +1,43 @@
+package com.bluelinelabs.conductor.rxlifecycle2;
+
+import androidx.annotation.NonNull;
+import com.trello.rxlifecycle2.LifecycleTransformer;
+import com.trello.rxlifecycle2.OutsideLifecycleException;
+import com.trello.rxlifecycle2.RxLifecycle;
+import io.reactivex.Observable;
+import io.reactivex.functions.Function;
+
+public class RxControllerLifecycle {
+
+    /**
+     * Binds the given source to a Controller lifecycle. This is the Controller version of
+     * {@link com.trello.rxlifecycle2.android.RxLifecycleAndroid#bindFragment(Observable)}.
+     *
+     * @param lifecycle the lifecycle sequence of a Controller
+     * @return a reusable {@link io.reactivex.ObservableTransformer} that unsubscribes the source during the Controller lifecycle
+     */
+    public static <T> LifecycleTransformer<T> bindController(@NonNull final Observable<ControllerEvent> lifecycle) {
+        return RxLifecycle.bind(lifecycle, CONTROLLER_LIFECYCLE);
+    }
+
+    private static final Function<ControllerEvent, ControllerEvent> CONTROLLER_LIFECYCLE =
+        new Function<ControllerEvent, ControllerEvent>() {
+            @Override
+            public ControllerEvent apply(ControllerEvent lastEvent) {
+                switch (lastEvent) {
+                    case CREATE:
+                        return ControllerEvent.DESTROY;
+                    case CONTEXT_AVAILABLE:
+                        return ControllerEvent.CONTEXT_UNAVAILABLE;
+                    case ATTACH:
+                        return ControllerEvent.DETACH;
+                    case CREATE_VIEW:
+                        return ControllerEvent.DESTROY_VIEW;
+                    case DETACH:
+                        return ControllerEvent.DESTROY;
+                    default:
+                        throw new OutsideLifecycleException("Cannot bind to Controller lifecycle when outside of it.");
+                }
+            }
+        };
+}
@@ -0,0 +1,24 @@
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode Integer.parseInt(project.VERSION_CODE)
+        versionName project.VERSION_NAME
+    }
+}
+
+dependencies {
+    implementation rootProject.ext.androidxAppCompat
+    implementation rootProject.ext.androidxCollection
+    api rootProject.ext.androidxTransition
+    implementation project(':conductor')
+}
+
+ext.artifactId = 'conductor-androidx-transition'
+
+apply from: rootProject.file('dependencies.gradle')
+apply plugin: "com.vanniktech.maven.publish"
@@ -0,0 +1,3 @@
+POM_NAME=Conductor AndroidX Transition Extensions
+POM_ARTIFACT_ID=conductor-transition-androidx
+POM_PACKAGING=aar
@@ -0,0 +1,3 @@
+<manifest package="com.bluelinelabs.conductor.androidxtransition">
+    <application />
+</manifest>
@@ -0,0 +1,656 @@
+package com.bluelinelabs.conductor.changehandler.androidxtransition;
+
+import android.graphics.Rect;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.ViewTreeObserver;
+import android.view.ViewTreeObserver.OnPreDrawListener;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.collection.ArrayMap;
+import androidx.core.app.SharedElementCallback;
+import androidx.core.view.ViewCompat;
+import androidx.core.view.ViewGroupCompat;
+import androidx.transition.Transition;
+import androidx.transition.TransitionSet;
+
+import com.bluelinelabs.conductor.Controller;
+import com.bluelinelabs.conductor.ControllerChangeHandler;
+import com.bluelinelabs.conductor.internal.TransitionUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A TransitionChangeHandler that facilitates using different Transitions for the entering view, the exiting view,
+ * and shared elements between the two.
+ * <p/>
+ * Note that this class uses the <b>androidx</b> {@link Transition}. If you're using Android's platform transitions,
+ * consider using the {@code SharedElementTransitionChangeHandler} provided by the {@code android-transitions} Conductor module.
+ */
+// Much of this class is based on FragmentTransition.java and FragmentTransitionCompat21.java from the Android support library
+public abstract class SharedElementTransitionChangeHandler extends TransitionChangeHandler {
+
+    // A map of from -> to names. Generally these will be the same.
+    @NonNull  final ArrayMap<String, String> sharedElementNames = new ArrayMap<>();
+
+    @NonNull  final List<String> waitForTransitionNames = new ArrayList<>();
+    @NonNull  final List<ViewParentPair> removedViews = new ArrayList<>();
+
+    @Nullable Transition exitTransition;
+    @Nullable Transition enterTransition;
+    @Nullable Transition sharedElementTransition;
+    @Nullable private SharedElementCallback exitTransitionCallback;
+    @Nullable private SharedElementCallback enterTransitionCallback;
+
+    @NonNull
+    @Override
+    protected final Transition getTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush) {
+        exitTransition = getExitTransition(container, from, to, isPush);
+        enterTransition = getEnterTransition(container, from, to, isPush);
+        sharedElementTransition = getSharedElementTransition(container, from, to, isPush);
+        exitTransitionCallback = getExitTransitionCallback(container, from, to, isPush);
+        enterTransitionCallback = getEnterTransitionCallback(container, from, to, isPush);
+
+        if (enterTransition == null && sharedElementTransition == null && exitTransition == null) {
+            throw new IllegalStateException("SharedElementTransitionChangeHandler must have at least one transaction.");
+        }
+
+        return mergeTransitions(isPush);
+    }
+
+    @Override
+    public void prepareForTransition(@NonNull final ViewGroup container, @Nullable final View from, @Nullable final View to, @NonNull final Transition transition, final boolean isPush, @NonNull final OnTransitionPreparedListener onTransitionPreparedListener) {
+        OnTransitionPreparedListener listener = new OnTransitionPreparedListener() {
+            @Override
+            public void onPrepared() {
+                configureTransition(container, from, to, transition, isPush);
+                onTransitionPreparedListener.onPrepared();
+            }
+        };
+
+        configureSharedElements(container, from, to, isPush);
+
+        if (to != null && to.getParent() == null && waitForTransitionNames.size() > 0) {
+            waitOnAllTransitionNames(to, listener);
+            container.addView(to);
+        } else {
+            listener.onPrepared();
+        }
+    }
+
+    @Override
+    public final void executePropertyChanges(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, @Nullable Transition transition, boolean isPush) {
+        if (to != null && removedViews.size() > 0) {
+            to.setVisibility(View.VISIBLE);
+
+            for (ViewParentPair removedView : removedViews) {
+                removedView.parent.addView(removedView.view);
+            }
+
+            removedViews.clear();
+        }
+
+        super.executePropertyChanges(container, from, to, transition, isPush);
+    }
+
+    @Override
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
+        super.onAbortPush(newHandler, newTop);
+
+        removedViews.clear();
+    }
+
+    void configureTransition(@NonNull final ViewGroup container, @Nullable View from, @Nullable View to, @NonNull final Transition transition, boolean isPush) {
+        final View nonExistentView = new View(container.getContext());
+
+        List<View> fromSharedElements = new ArrayList<>();
+        List<View> toSharedElements = new ArrayList<>();
+
+        configureSharedElements(container, nonExistentView, to, from, isPush, fromSharedElements, toSharedElements);
+
+        List<View> exitingViews = exitTransition != null ? configureEnteringExitingViews(exitTransition, from, fromSharedElements, nonExistentView) : null;
+        if (exitingViews == null || exitingViews.isEmpty()) {
+            exitTransition = null;
+        }
+
+        if (enterTransition != null) {
+            enterTransition.addTarget(nonExistentView);
+        }
+
+        final List<View> enteringViews = new ArrayList<>();
+        scheduleRemoveTargets(transition, enterTransition, enteringViews, exitTransition, exitingViews, sharedElementTransition, toSharedElements);
+        scheduleTargetChange(container, to, nonExistentView, toSharedElements, enteringViews, exitingViews);
+
+        setNameOverrides(container, toSharedElements);
+        scheduleNameReset(container, toSharedElements);
+    }
+
+    private void waitOnAllTransitionNames(@NonNull final View to, @NonNull final OnTransitionPreparedListener onTransitionPreparedListener) {
+        OnPreDrawListener onPreDrawListener = new OnPreDrawListener() {
+            boolean addedSubviewListeners;
+
+            @Override
+            public boolean onPreDraw() {
+                List<View> foundViews = new ArrayList<>();
+                boolean allViewsFound = true;
+                for (String transitionName : waitForTransitionNames) {
+                    View namedView = TransitionUtils.findNamedView(to, transitionName);
+                    if (namedView != null) {
+                        foundViews.add(TransitionUtils.findNamedView(to, transitionName));
+                    } else {
+                        allViewsFound = false;
+                        break;
+                    }
+                }
+
+                if (allViewsFound && !addedSubviewListeners) {
+                    addedSubviewListeners = true;
+                    waitOnChildTransitionNames(to, foundViews, this, onTransitionPreparedListener);
+                }
+
+                return false;
+            }
+        };
+
+        to.getViewTreeObserver().addOnPreDrawListener(onPreDrawListener);
+    }
+
+    void waitOnChildTransitionNames(@NonNull final View to, @NonNull List<View> foundViews, @NonNull final OnPreDrawListener parentPreDrawListener, @NonNull final OnTransitionPreparedListener onTransitionPreparedListener) {
+        for (final View view : foundViews) {
+            OneShotPreDrawListener.add(true, view, new Runnable() {
+                @Override
+                public void run() {
+                    waitForTransitionNames.remove(ViewCompat.getTransitionName(view));
+
+                    removedViews.add(new ViewParentPair(view, (ViewGroup)view.getParent()));
+                    ((ViewGroup)view.getParent()).removeView(view);
+
+                    if (waitForTransitionNames.size() == 0) {
+                        to.getViewTreeObserver().removeOnPreDrawListener(parentPreDrawListener);
+                        to.setVisibility(View.INVISIBLE);
+                        onTransitionPreparedListener.onPrepared();
+                    }
+                }
+            });
+        }
+    }
+
+    private void scheduleTargetChange(@NonNull final ViewGroup container, @Nullable final View to, @NonNull final View nonExistentView,
+                                      @NonNull final List<View> toSharedElements, @NonNull final List<View> enteringViews, @Nullable final List<View> exitingViews) {
+        OneShotPreDrawListener.add(true, container, new Runnable() {
+            @Override
+            public void run() {
+                if (enterTransition != null) {
+                    enterTransition.removeTarget(nonExistentView);
+                    List<View> views = configureEnteringExitingViews(enterTransition, to, toSharedElements, nonExistentView);
+                    enteringViews.addAll(views);
+                }
+
+                if (exitingViews != null) {
+                    if (exitTransition != null) {
+                        List<View> tempExiting = new ArrayList<>();
+                        tempExiting.add(nonExistentView);
+                        TransitionUtils.replaceTargets(exitTransition, exitingViews, tempExiting);
+                    }
+                    exitingViews.clear();
+                    exitingViews.add(nonExistentView);
+                }
+            }
+        });
+    }
+
+    private Transition mergeTransitions(boolean isPush) {
+        boolean overlap = enterTransition == null || exitTransition == null || allowTransitionOverlap(isPush);
+
+        if (overlap) {
+            return TransitionUtils.mergeTransitions(TransitionSet.ORDERING_TOGETHER, exitTransition, enterTransition, sharedElementTransition);
+        } else {
+            Transition staggered = TransitionUtils.mergeTransitions(TransitionSet.ORDERING_SEQUENTIAL, exitTransition, enterTransition);
+            return TransitionUtils.mergeTransitions(TransitionSet.ORDERING_TOGETHER, staggered, sharedElementTransition);
+        }
+    }
+
+    @NonNull List<View> configureEnteringExitingViews(@NonNull Transition transition, @Nullable View view, @NonNull List<View> sharedElements, @NonNull View nonExistentView) {
+        List<View> viewList = new ArrayList<>();
+        if (view != null) {
+            captureTransitioningViews(viewList, view);
+        }
+        viewList.removeAll(sharedElements);
+        if (!viewList.isEmpty()) {
+            viewList.add(nonExistentView);
+            TransitionUtils.addTargets(transition, viewList);
+        }
+        return viewList;
+    }
+
+    private void configureSharedElements(@NonNull ViewGroup container, @NonNull final View nonExistentView, @Nullable final View to, @Nullable View from,
+                                         final boolean isPush, @NonNull final List<View> fromSharedElements, @NonNull final List<View> toSharedElements) {
+
+        if (to == null || from == null) {
+            return;
+        }
+
+        ArrayMap<String, View> capturedFromSharedElements = captureFromSharedElements(from);
+
+        if (sharedElementNames.isEmpty()) {
+            sharedElementTransition = null;
+        } else if (capturedFromSharedElements != null) {
+            fromSharedElements.addAll(capturedFromSharedElements.values());
+        }
+
+        if (enterTransition == null && exitTransition == null && sharedElementTransition == null) {
+            return;
+        }
+
+        callSharedElementStartEnd(capturedFromSharedElements, true);
+
+        final Rect toEpicenter;
+        if (sharedElementTransition != null) {
+            toEpicenter = new Rect();
+            TransitionUtils.setTargets(sharedElementTransition, nonExistentView, fromSharedElements);
+            setFromEpicenter(capturedFromSharedElements);
+            if (enterTransition != null) {
+                enterTransition.setEpicenterCallback(new Transition.EpicenterCallback() {
+                    @Override
+                    public Rect onGetEpicenter(Transition transition) {
+                        if (toEpicenter.isEmpty()) {
+                            return null;
+                        }
+                        return toEpicenter;
+                    }
+                });
+            }
+        } else {
+            toEpicenter = null;
+        }
+
+        OneShotPreDrawListener.add(true, container, new Runnable() {
+            @Override
+            public void run() {
+                ArrayMap<String, View> capturedToSharedElements = captureToSharedElements(to, isPush);
+
+                if (capturedToSharedElements != null) {
+                    toSharedElements.addAll(capturedToSharedElements.values());
+                    toSharedElements.add(nonExistentView);
+                }
+
+                callSharedElementStartEnd(capturedToSharedElements, false);
+                if (sharedElementTransition != null) {
+                    sharedElementTransition.getTargets().clear();
+                    sharedElementTransition.getTargets().addAll(toSharedElements);
+                    TransitionUtils.replaceTargets(sharedElementTransition, fromSharedElements, toSharedElements);
+
+                    final View toEpicenterView = getToEpicenterView(capturedToSharedElements);
+                    if (toEpicenterView != null && toEpicenter != null) {
+                        TransitionUtils.getBoundsOnScreen(toEpicenterView, toEpicenter);
+                    }
+                }
+            }
+        });
+    }
+
+    @Nullable View getToEpicenterView(@Nullable ArrayMap<String, View> toSharedElements) {
+        if (enterTransition != null && sharedElementNames.size() > 0 && toSharedElements != null) {
+            return toSharedElements.get(sharedElementNames.valueAt(0));
+        }
+        return null;
+    }
+
+    private void setFromEpicenter(@Nullable ArrayMap<String, View> fromSharedElements) {
+        if (sharedElementNames.size() > 0 && fromSharedElements != null) {
+            final View fromEpicenterView = fromSharedElements.get(sharedElementNames.keyAt(0));
+
+            if (sharedElementTransition != null) {
+                TransitionUtils.setEpicenter(sharedElementTransition, fromEpicenterView);
+            }
+
+            if (exitTransition != null) {
+                TransitionUtils.setEpicenter(exitTransition, fromEpicenterView);
+            }
+        }
+    }
+
+    @Nullable ArrayMap<String, View> captureToSharedElements(@Nullable final View to, boolean isPush) {
+        if (sharedElementNames.isEmpty() || sharedElementTransition == null || to == null) {
+            sharedElementNames.clear();
+            return null;
+        }
+
+        final ArrayMap<String, View> toSharedElements = new ArrayMap<>();
+        TransitionUtils.findNamedViews(toSharedElements, to);
+        for (ViewParentPair removedView : removedViews) {
+            toSharedElements.put(ViewCompat.getTransitionName(removedView.view), removedView.view);
+        }
+
+        final List<String> names = new ArrayList<>(sharedElementNames.values());
+
+        toSharedElements.retainAll(names);
+        if (enterTransitionCallback != null) {
+            enterTransitionCallback.onMapSharedElements(names, toSharedElements);
+            for (int i = names.size() - 1; i >= 0; i--) {
+                String name = names.get(i);
+                View view = toSharedElements.get(name);
+                if (view == null) {
+                    String key = findKeyForValue(sharedElementNames, name);
+                    if (key != null) {
+                        sharedElementNames.remove(key);
+                    }
+                } else if (!name.equals(ViewCompat.getTransitionName(view))) {
+                    String key = findKeyForValue(sharedElementNames, name);
+                    if (key != null) {
+                        sharedElementNames.put(key, ViewCompat.getTransitionName(view));
+                    }
+                }
+            }
+        } else {
+            for (int i = sharedElementNames.size() - 1; i >= 0; i--) {
+                final String targetName = sharedElementNames.valueAt(i);
+                if (!toSharedElements.containsKey(targetName)) {
+                    sharedElementNames.removeAt(i);
+                }
+            }
+        }
+        return toSharedElements;
+    }
+
+    @Nullable String findKeyForValue(@NonNull ArrayMap<String, String> map, @NonNull String value) {
+        final int numElements = map.size();
+        for (int i = 0; i < numElements; i++) {
+            if (value.equals(map.valueAt(i))) {
+                return map.keyAt(i);
+            }
+        }
+        return null;
+    }
+
+    @Nullable
+    private ArrayMap<String, View> captureFromSharedElements(@NonNull View from) {
+        if (sharedElementNames.isEmpty() || sharedElementTransition == null) {
+            sharedElementNames.clear();
+            return null;
+        }
+
+        final ArrayMap<String, View> fromSharedElements = new ArrayMap<>();
+        TransitionUtils.findNamedViews(fromSharedElements, from);
+
+        final List<String> names = new ArrayList<>(sharedElementNames.keySet());
+
+        fromSharedElements.retainAll(names);
+        if (exitTransitionCallback != null) {
+            exitTransitionCallback.onMapSharedElements(names, fromSharedElements);
+            for (int i = names.size() - 1; i >= 0; i--) {
+                String name = names.get(i);
+                View view = fromSharedElements.get(name);
+                if (view == null) {
+                    sharedElementNames.remove(name);
+                } else if (!name.equals(ViewCompat.getTransitionName(view))) {
+                    String targetValue = sharedElementNames.remove(name);
+                    sharedElementNames.put(ViewCompat.getTransitionName(view), targetValue);
+                }
+            }
+        } else {
+            sharedElementNames.retainAll(fromSharedElements.keySet());
+        }
+        return fromSharedElements;
+    }
+
+    void callSharedElementStartEnd(@Nullable ArrayMap<String, View> sharedElements, boolean isStart) {
+        if (enterTransitionCallback != null) {
+            final int count = sharedElements == null ? 0 : sharedElements.size();
+            List<View> views = new ArrayList<>(count);
+            List<String> names = new ArrayList<>(count);
+            for (int i = 0; i < count; i++) {
+                names.add(sharedElements.keyAt(i));
+                views.add(sharedElements.valueAt(i));
+            }
+            if (isStart) {
+                enterTransitionCallback.onSharedElementStart(names, views, null);
+            } else {
+                enterTransitionCallback.onSharedElementEnd(names, views, null);
+            }
+        }
+    }
+
+    private void captureTransitioningViews(@NonNull List<View> transitioningViews, @NonNull View view) {
+        if (view.getVisibility() == View.VISIBLE) {
+            if (view instanceof ViewGroup) {
+                ViewGroup viewGroup = (ViewGroup) view;
+                if (ViewGroupCompat.isTransitionGroup(viewGroup)) {
+                    transitioningViews.add(viewGroup);
+                } else {
+                    int count = viewGroup.getChildCount();
+                    for (int i = 0; i < count; i++) {
+                        View child = viewGroup.getChildAt(i);
+                        captureTransitioningViews(transitioningViews, child);
+                    }
+                }
+            } else {
+                transitioningViews.add(view);
+            }
+        }
+    }
+
+    private void scheduleRemoveTargets(@NonNull final Transition overallTransition,
+                                       @Nullable final Transition enterTransition, @Nullable final List<View> enteringViews,
+                                       @Nullable final Transition exitTransition, @Nullable final List<View> exitingViews,
+                                       @Nullable final Transition sharedElementTransition, @Nullable final List<View> toSharedElements) {
+        overallTransition.addListener(new Transition.TransitionListener() {
+            @Override
+            public void onTransitionStart(Transition transition) {
+                if (enterTransition != null && enteringViews != null) {
+                    TransitionUtils.replaceTargets(enterTransition, enteringViews, null);
+                }
+                if (exitTransition != null && exitingViews != null) {
+                    TransitionUtils.replaceTargets(exitTransition, exitingViews, null);
+                }
+                if (sharedElementTransition != null && toSharedElements != null) {
+                    TransitionUtils.replaceTargets(sharedElementTransition, toSharedElements, null);
+                }
+            }
+
+            @Override
+            public void onTransitionEnd(Transition transition) { }
+
+            @Override
+            public void onTransitionCancel(Transition transition) { }
+
+            @Override
+            public void onTransitionPause(Transition transition) { }
+
+            @Override
+            public void onTransitionResume(Transition transition) { }
+        });
+    }
+
+    private void setNameOverrides(@NonNull final View container, @NonNull final List<View> toSharedElements) {
+        OneShotPreDrawListener.add(true, container, new Runnable() {
+            @Override
+            public void run() {
+                final int numSharedElements = toSharedElements.size();
+                for (int i = 0; i < numSharedElements; i++) {
+                    View view = toSharedElements.get(i);
+                    String name = ViewCompat.getTransitionName(view);
+                    if (name != null) {
+                        String inName = findKeyForValue(sharedElementNames, name);
+                        ViewCompat.setTransitionName(view, inName);
+                    }
+                }
+            }
+        });
+    }
+
+    private void scheduleNameReset(@NonNull final ViewGroup container, @NonNull final List<View> toSharedElements) {
+        OneShotPreDrawListener.add(true, container, new Runnable() {
+            @Override
+            public void run() {
+                final int numSharedElements = toSharedElements.size();
+                for (int i = 0; i < numSharedElements; i++) {
+                    final View view = toSharedElements.get(i);
+                    final String name = ViewCompat.getTransitionName(view);
+                    final String inName = sharedElementNames.get(name);
+                    ViewCompat.setTransitionName(view, inName);
+                }
+            }
+        });
+    }
+
+    /**
+     * Will be called when views are ready to have their shared elements configured. Within this method one of the addSharedElement methods
+     * should be called for each shared element that will be used. If one or more of these shared elements will not instantly be available in
+     * the incoming view (for ex, in a RecyclerView), waitOnSharedElementNamed can be called to delay the transition until everything is available.
+     */
+    public abstract void configureSharedElements(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return the transition that will be used on the exiting ("from") view, if one is desired.
+     */
+    @Nullable
+    public abstract Transition getExitTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return the transition that will be used on shared elements between the from and to views.
+     */
+    @Nullable
+    public abstract Transition getSharedElementTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return the transition that will be used on the entering ("to") view, if one is desired.
+     */
+    @Nullable
+    public abstract Transition getEnterTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return a callback that can be used to customize transition behavior of the shared element transition for the "from" view.
+     */
+    @Nullable
+    public SharedElementCallback getExitTransitionCallback(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush) {
+        return null;
+    }
+
+    /**
+     * Should return a callback that can be used to customize transition behavior of the shared element transition for the "to" view.
+     */
+    @Nullable
+    public SharedElementCallback getEnterTransitionCallback(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush) {
+        return null;
+    }
+
+    /**
+     * Should return whether or not the the exit transition and enter transition should overlap. If true,
+     * the enter transition will start as soon as possible. Otherwise, the enter transition will wait until the
+     * completion of the exit transition. Defaults to true.
+     */
+    public boolean allowTransitionOverlap(boolean isPush) {
+        return true;
+    }
+
+    /**
+     * Used to register an element that will take part in the shared element transition.
+     *
+     * @param name The transition name that is used for both the entering and exiting views.
+     */
+    protected final void addSharedElement(@NonNull String name) {
+        sharedElementNames.put(name, name);
+    }
+
+    /**
+     * Used to register an element that will take part in the shared element transition. Maps the name used in the
+     * "from" view to the name used in the "to" view if they are not the same.
+     *
+     * @param fromName The transition name used in the "from" view
+     * @param toName The transition name used in the "to" view
+     */
+    protected final void addSharedElement(@NonNull String fromName, @NonNull String toName) {
+        sharedElementNames.put(fromName, toName);
+    }
+
+    /**
+     * Used to register an element that will take part in the shared element transition. Maps the name used in the
+     * "from" view to the name used in the "to" view if they are not the same.
+     *
+     * @param sharedElement The view from the "from" view that will take part in the shared element transition
+     * @param toName The transition name used in the "to" view
+     */
+    protected final void addSharedElement(@NonNull View sharedElement, @NonNull String toName) {
+        String transitionName = ViewCompat.getTransitionName(sharedElement);
+        if (transitionName == null) {
+            throw new IllegalArgumentException("Unique transitionNames are required for all sharedElements");
+        }
+        sharedElementNames.put(transitionName, toName);
+    }
+
+    /**
+     * The transition will be delayed until the view with the name passed in is available in the "to" hierarchy. This is
+     * particularly useful for views that don't load instantly, like RecyclerViews. Note that using this method can
+     * potentially lock up your app indefinitely if the view never loads!
+     */
+    protected final void waitOnSharedElementNamed(@NonNull String name) {
+        if (!sharedElementNames.values().contains(name)) {
+            throw new IllegalStateException("Can't wait on a shared element that hasn't been registered using addSharedElement");
+        }
+        waitForTransitionNames.add(name);
+    }
+
+    private static class OneShotPreDrawListener implements OnPreDrawListener, View.OnAttachStateChangeListener {
+
+        private final View view;
+        private ViewTreeObserver viewTreeObserver;
+        private final Runnable runnable;
+        private final boolean preDrawReturnValue;
+
+        private OneShotPreDrawListener(boolean preDrawReturnValue, @NonNull View view, @NonNull Runnable runnable) {
+            this.preDrawReturnValue = preDrawReturnValue;
+            this.view = view;
+            viewTreeObserver = view.getViewTreeObserver();
+            this.runnable = runnable;
+        }
+
+        @NonNull
+        public static OneShotPreDrawListener add(boolean preDrawReturnValue, @NonNull View view, @NonNull Runnable runnable) {
+            OneShotPreDrawListener listener = new OneShotPreDrawListener(preDrawReturnValue, view, runnable);
+            view.getViewTreeObserver().addOnPreDrawListener(listener);
+            view.addOnAttachStateChangeListener(listener);
+            return listener;
+        }
+
+        @Override
+        public boolean onPreDraw() {
+            removeListener();
+            runnable.run();
+            return preDrawReturnValue;
+        }
+
+        private void removeListener() {
+            if (viewTreeObserver.isAlive()) {
+                viewTreeObserver.removeOnPreDrawListener(this);
+            } else {
+                view.getViewTreeObserver().removeOnPreDrawListener(this);
+            }
+            view.removeOnAttachStateChangeListener(this);
+        }
+
+        @Override
+        public void onViewAttachedToWindow(View v) {
+            viewTreeObserver = v.getViewTreeObserver();
+        }
+
+        @Override
+        public void onViewDetachedFromWindow(View v) {
+            removeListener();
+        }
+
+    }
+
+    private static class ViewParentPair {
+        @NonNull final View view;
+        @NonNull final ViewGroup parent;
+
+        ViewParentPair(@NonNull View view, ViewGroup parent) {
+            this.view = view;
+            this.parent = parent;
+        }
+    }
+
+}
@@ -0,0 +1,153 @@
+package com.bluelinelabs.conductor.changehandler.androidxtransition;
+
+import android.view.View;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.transition.Transition;
+import androidx.transition.TransitionManager;
+
+import com.bluelinelabs.conductor.Controller;
+import com.bluelinelabs.conductor.ControllerChangeHandler;
+
+/**
+ * A base {@link ControllerChangeHandler} that facilitates using {@link Transition}s to replace Controller Views.
+ * <p/>
+ * Note that this class uses the <b>androidx</b> {@link Transition}. If you're using Android's platform transitions,
+ * consider using the {@code TransitionChangeHandler} provided by the {@code android-transitions} Conductor module.
+ */
+public abstract class TransitionChangeHandler extends ControllerChangeHandler {
+
+    public interface OnTransitionPreparedListener {
+        void onPrepared();
+    }
+
+    boolean canceled;
+    private boolean needsImmediateCompletion;
+
+    /**
+     * Should be overridden to return the Transition to use while replacing Views.
+     *
+     * @param container The container these Views are hosted in
+     * @param from      The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to        The next View that should be put in the container or {@code null} if no Controller is being transitioned to
+     * @param isPush    True if this is a push transaction, false if it's a pop
+     */
+    @NonNull
+    protected abstract Transition getTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    @Override
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
+        super.onAbortPush(newHandler, newTop);
+
+        canceled = true;
+    }
+
+    @Override
+    public void completeImmediately() {
+        super.completeImmediately();
+
+        needsImmediateCompletion = true;
+    }
+
+    @Nullable
+    private ControllerChangeCompletedListener listener;
+
+    @Override
+    public void performChange(@NonNull final ViewGroup container, @Nullable final View from, @Nullable final View to, final boolean isPush, @NonNull final ControllerChangeCompletedListener changeListener) {
+        listener = changeListener;
+        if (canceled) {
+            changeListener.onChangeCompleted();
+            return;
+        }
+        if (needsImmediateCompletion) {
+            executePropertyChanges(container, from, to, null, isPush);
+            changeListener.onChangeCompleted();
+            return;
+        }
+
+        final Runnable onTransitionNotStarted = new Runnable() {
+            @Override
+            public void run() {
+                changeListener.onChangeCompleted();
+            }
+        };
+
+        final Transition transition = getTransition(container, from, to, isPush);
+        transition.addListener(new Transition.TransitionListener() {
+            @Override
+            public void onTransitionStart(Transition transition) {
+                container.removeCallbacks(onTransitionNotStarted);
+            }
+
+            @Override
+            public void onTransitionEnd(Transition transition) {
+                listener.onChangeCompleted();
+                listener = null;
+            }
+
+            @Override
+            public void onTransitionCancel(Transition transition) {
+                listener.onChangeCompleted();
+                listener = null;
+            }
+
+            @Override
+            public void onTransitionPause(Transition transition) { }
+
+            @Override
+            public void onTransitionResume(Transition transition) { }
+        });
+
+        prepareForTransition(container, from, to, transition, isPush, new OnTransitionPreparedListener() {
+            @Override
+            public void onPrepared() {
+                if (!canceled) {
+                    TransitionManager.beginDelayedTransition(container, transition);
+                    executePropertyChanges(container, from, to, transition, isPush);
+                    container.post(onTransitionNotStarted);
+                }
+            }
+        });
+    }
+
+    @Override
+    public boolean removesFromViewOnPush() {
+        return true;
+    }
+
+    /**
+     * Called before a transition occurs. This can be used to reorder views, set their transition names, etc. The transition will begin
+     * when {@code onTransitionPreparedListener} is called.
+     *
+     * @param container  The container these Views are hosted in
+     * @param from       The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to         The next View that should be put in the container or {@code null} if no Controller is being transitioned to
+     * @param transition The transition that is being prepared for
+     * @param isPush     True if this is a push transaction, false if it's a pop
+     */
+    public void prepareForTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, @NonNull Transition transition, boolean isPush, @NonNull OnTransitionPreparedListener onTransitionPreparedListener) {
+        onTransitionPreparedListener.onPrepared();
+    }
+
+    /**
+     * This should set all view properties needed for the transition to work properly. By default it removes the "from" view
+     * and adds the "to" view.
+     *
+     * @param container  The container these Views are hosted in
+     * @param from       The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to         The next View that should be put in the container or {@code null} if no Controller is being transitioned to
+     * @param transition The transition with which {@code TransitionManager.beginDelayedTransition} has been called. This will be null only if another ControllerChangeHandler immediately overrides this one.
+     * @param isPush     True if this is a push transaction, false if it's a pop
+     */
+    public void executePropertyChanges(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, @Nullable Transition transition, boolean isPush) {
+        if (from != null && (removesFromViewOnPush() || !isPush) && from.getParent() == container) {
+            container.removeView(from);
+        }
+        if (to != null && to.getParent() == null) {
+            container.addView(to);
+        }
+    }
+
+}
@@ -0,0 +1,184 @@
+package com.bluelinelabs.conductor.internal;
+
+import android.graphics.Rect;
+import android.view.View;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.core.view.ViewCompat;
+import androidx.transition.Transition;
+import androidx.transition.TransitionSet;
+
+import java.util.List;
+import java.util.Map;
+
+public class TransitionUtils {
+
+    public static void findNamedViews(@NonNull Map<String, View> namedViews, View view) {
+        if (view.getVisibility() == View.VISIBLE) {
+            String transitionName = ViewCompat.getTransitionName(view);
+            if (transitionName != null) {
+                namedViews.put(transitionName, view);
+            }
+
+            if (view instanceof ViewGroup) {
+                ViewGroup viewGroup = (ViewGroup) view;
+                int childCount = viewGroup.getChildCount();
+                for (int i = 0; i < childCount; i++) {
+                    View child = viewGroup.getChildAt(i);
+                    findNamedViews(namedViews, child);
+                }
+            }
+        }
+    }
+
+    @Nullable
+    public static View findNamedView(@NonNull View view, @NonNull String transitionName) {
+        if (transitionName.equals(ViewCompat.getTransitionName(view))) {
+            return view;
+        }
+
+        if (view instanceof ViewGroup) {
+            ViewGroup viewGroup = (ViewGroup) view;
+            int childCount = viewGroup.getChildCount();
+            for (int i = 0; i < childCount; i++) {
+                View viewWithTransitionName = findNamedView(viewGroup.getChildAt(i), transitionName);
+                if (viewWithTransitionName != null) {
+                    return viewWithTransitionName;
+                }
+            }
+        }
+
+        return null;
+    }
+
+    public static void setEpicenter(@NonNull Transition transition, @Nullable View view) {
+        if (view != null) {
+            final Rect epicenter = new Rect();
+            getBoundsOnScreen(view, epicenter);
+            transition.setEpicenterCallback(new Transition.EpicenterCallback() {
+                @Override
+                public Rect onGetEpicenter(Transition transition) {
+                    return epicenter;
+                }
+            });
+        }
+    }
+
+    public static void getBoundsOnScreen(@NonNull View view, @NonNull Rect epicenter) {
+        int[] loc = new int[2];
+        view.getLocationOnScreen(loc);
+        epicenter.set(loc[0], loc[1], loc[0] + view.getWidth(), loc[1] + view.getHeight());
+    }
+
+    public static void setTargets(@NonNull Transition transition, @NonNull View nonExistentView, @NonNull List<View> sharedViews) {
+        final List<View> views = transition.getTargets();
+        views.clear();
+        final int count = sharedViews.size();
+        for (int i = 0; i < count; i++) {
+            final View view = sharedViews.get(i);
+            bfsAddViewChildren(views, view);
+        }
+        views.add(nonExistentView);
+        sharedViews.add(nonExistentView);
+        addTargets(transition, sharedViews);
+    }
+
+    public static void addTargets(@Nullable Transition transition, @NonNull List<View> views) {
+        if (transition == null) {
+            return;
+        }
+        if (transition instanceof TransitionSet) {
+            TransitionSet set = (TransitionSet) transition;
+            int numTransitions = set.getTransitionCount();
+            for (int i = 0; i < numTransitions; i++) {
+                Transition child = set.getTransitionAt(i);
+                addTargets(child, views);
+            }
+        } else if (!hasSimpleTarget(transition)) {
+            List<View> targets = transition.getTargets();
+            if (isNullOrEmpty(targets)) {
+                int numViews = views.size();
+                for (int i = 0; i < numViews; i++) {
+                    transition.addTarget(views.get(i));
+                }
+            }
+        }
+    }
+
+    public static void replaceTargets(@NonNull Transition transition, @NonNull List<View> oldTargets, @Nullable List<View> newTargets) {
+        if (transition instanceof TransitionSet) {
+            TransitionSet set = (TransitionSet) transition;
+            int numTransitions = set.getTransitionCount();
+            for (int i = 0; i < numTransitions; i++) {
+                Transition child = set.getTransitionAt(i);
+                replaceTargets(child, oldTargets, newTargets);
+            }
+        } else if (!TransitionUtils.hasSimpleTarget(transition)) {
+            List<View> targets = transition.getTargets();
+            if (targets != null && targets.size() == oldTargets.size() && targets.containsAll(oldTargets)) {
+                final int targetCount = newTargets == null ? 0 : newTargets.size();
+                for (int i = 0; i < targetCount; i++) {
+                    transition.addTarget(newTargets.get(i));
+                }
+                for (int i = oldTargets.size() - 1; i >= 0; i--) {
+                    transition.removeTarget(oldTargets.get(i));
+                }
+            }
+        }
+    }
+
+    private static void bfsAddViewChildren(@NonNull final List<View> views, @NonNull final View startView) {
+        final int startIndex = views.size();
+        if (containedBeforeIndex(views, startView, startIndex)) {
+            return; // This child is already in the list, so all its children are also.
+        }
+        views.add(startView);
+        for (int index = startIndex; index < views.size(); index++) {
+            final View view = views.get(index);
+            if (view instanceof ViewGroup) {
+                ViewGroup viewGroup = (ViewGroup) view;
+                final int childCount = viewGroup.getChildCount();
+                for (int childIndex = 0; childIndex < childCount; childIndex++) {
+                    final View child = viewGroup.getChildAt(childIndex);
+                    if (!containedBeforeIndex(views, child, startIndex)) {
+                        views.add(child);
+                    }
+                }
+            }
+        }
+    }
+
+    private static boolean containedBeforeIndex(@NonNull List<View> views, View view, int maxIndex) {
+        for (int i = 0; i < maxIndex; i++) {
+            if (views.get(i) == view) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public static boolean hasSimpleTarget(@NonNull Transition transition) {
+        return !isNullOrEmpty(transition.getTargetIds())
+                || !isNullOrEmpty(transition.getTargetNames())
+                || !isNullOrEmpty(transition.getTargetTypes());
+    }
+
+    private static boolean isNullOrEmpty(@Nullable List list) {
+        return list == null || list.isEmpty();
+    }
+
+    @NonNull
+    public static TransitionSet mergeTransitions(int ordering, Transition... transitions) {
+        TransitionSet transitionSet = new TransitionSet();
+        for (Transition transition : transitions) {
+            if (transition != null) {
+                transitionSet.addTransition(transition);
+            }
+        }
+        transitionSet.setOrdering(ordering);
+        return transitionSet;
+    }
+
+}
@@ -0,0 +1,21 @@
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode Integer.parseInt(project.VERSION_CODE)
+        versionName project.VERSION_NAME
+    }
+}
+
+dependencies {
+    implementation project(':conductor')
+}
+
+ext.artifactId = 'conductor-android-transition'
+
+apply from: rootProject.file('dependencies.gradle')
+apply plugin: "com.vanniktech.maven.publish"
@@ -0,0 +1,3 @@
+POM_NAME=Conductor Platform Transition Extensions
+POM_ARTIFACT_ID=conductor-transition-platform
+POM_PACKAGING=aar
@@ -0,0 +1,3 @@
+<manifest package="com.bluelinelabs.conductor.platformtransition">
+    <application />
+</manifest>
@@ -0,0 +1,647 @@
+package com.bluelinelabs.conductor.changehandler.platformtransition;
+
+import android.annotation.TargetApi;
+import android.app.SharedElementCallback;
+import android.graphics.Rect;
+import android.os.Build;
+import android.transition.Transition;
+import android.transition.Transition.TransitionListener;
+import android.transition.TransitionSet;
+import android.util.ArrayMap;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.ViewTreeObserver;
+import android.view.ViewTreeObserver.OnPreDrawListener;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import com.bluelinelabs.conductor.Controller;
+import com.bluelinelabs.conductor.ControllerChangeHandler;
+import com.bluelinelabs.conductor.internal.TransitionUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A TransitionChangeHandler that facilitates using different Transitions for the entering view, the exiting view,
+ * and shared elements between the two.
+ * <p/>
+ * Note that this class uses Android's <b>platform</b> {@link Transition}. If you're using androidx transitions, consider
+ * using the {@code SharedElementTransitionChangeHandler} provided by the {@code androidx-transitions} Conductor module.
+ */
+// Much of this class is based on FragmentTransition.java and FragmentTransitionCompat21.java from the Android support library
+@TargetApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class SharedElementTransitionChangeHandler extends TransitionChangeHandler {
+
+    // A map of from -> to names. Generally these will be the same.
+    @NonNull  final ArrayMap<String, String> sharedElementNames = new ArrayMap<>();
+
+    @NonNull  final List<String> waitForTransitionNames = new ArrayList<>();
+    @NonNull  final List<ViewParentPair> removedViews = new ArrayList<>();
+
+    @Nullable Transition exitTransition;
+    @Nullable Transition enterTransition;
+    @Nullable Transition sharedElementTransition;
+    @Nullable private SharedElementCallback exitTransitionCallback;
+    @Nullable private SharedElementCallback enterTransitionCallback;
+
+    @NonNull
+    @Override
+    protected final Transition getTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush) {
+        exitTransition = getExitTransition(container, from, to, isPush);
+        enterTransition = getEnterTransition(container, from, to, isPush);
+        sharedElementTransition = getSharedElementTransition(container, from, to, isPush);
+        exitTransitionCallback = getExitTransitionCallback(container, from, to, isPush);
+        enterTransitionCallback = getEnterTransitionCallback(container, from, to, isPush);
+
+        if (enterTransition == null && sharedElementTransition == null && exitTransition == null) {
+            throw new IllegalStateException("SharedElementTransitionChangeHandler must have at least one transaction.");
+        }
+
+        return mergeTransitions(isPush);
+    }
+
+    @Override
+    public void prepareForTransition(@NonNull final ViewGroup container, @Nullable final View from, @Nullable final View to, @NonNull final Transition transition, final boolean isPush, @NonNull final OnTransitionPreparedListener onTransitionPreparedListener) {
+        OnTransitionPreparedListener listener = () -> {
+            configureTransition(container, from, to, transition, isPush);
+            onTransitionPreparedListener.onPrepared();
+        };
+
+        configureSharedElements(container, from, to, isPush);
+
+        if (to != null && to.getParent() == null && waitForTransitionNames.size() > 0) {
+            waitOnAllTransitionNames(to, listener);
+            container.addView(to);
+        } else {
+            listener.onPrepared();
+        }
+    }
+
+    @Override
+    public final void executePropertyChanges(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, @Nullable Transition transition, boolean isPush) {
+        if (to != null && removedViews.size() > 0) {
+            to.setVisibility(View.VISIBLE);
+
+            for (ViewParentPair removedView : removedViews) {
+                removedView.parent.addView(removedView.view);
+            }
+
+            removedViews.clear();
+        }
+
+        super.executePropertyChanges(container, from, to, transition, isPush);
+    }
+
+    @Override
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
+        super.onAbortPush(newHandler, newTop);
+
+        removedViews.clear();
+    }
+
+    @Override
+    protected void onEnd() {
+        exitTransition = null;
+        enterTransition = null;
+        sharedElementTransition = null;
+    }
+
+    void configureTransition(@NonNull final ViewGroup container, @Nullable View from, @Nullable View to, @NonNull final Transition transition, boolean isPush) {
+        final View nonExistentView = new View(container.getContext());
+
+        List<View> fromSharedElements = new ArrayList<>();
+        List<View> toSharedElements = new ArrayList<>();
+
+        configureSharedElements(container, nonExistentView, to, from, isPush, fromSharedElements, toSharedElements);
+
+        List<View> exitingViews = exitTransition != null ? configureEnteringExitingViews(exitTransition, from, fromSharedElements, nonExistentView) : null;
+        if (exitingViews == null || exitingViews.isEmpty()) {
+            exitTransition = null;
+        }
+
+        if (enterTransition != null) {
+            enterTransition.addTarget(nonExistentView);
+        }
+
+        final List<View> enteringViews = new ArrayList<>();
+        scheduleRemoveTargets(transition, enterTransition, enteringViews, exitTransition, exitingViews, sharedElementTransition, toSharedElements);
+        scheduleTargetChange(container, to, nonExistentView, toSharedElements, enteringViews, exitingViews);
+
+        setNameOverrides(container, toSharedElements);
+        scheduleNameReset(container, toSharedElements);
+    }
+
+    private void waitOnAllTransitionNames(@NonNull final View to, @NonNull final OnTransitionPreparedListener onTransitionPreparedListener) {
+        OnPreDrawListener onPreDrawListener = new OnPreDrawListener() {
+            boolean addedSubviewListeners;
+
+            @Override
+            public boolean onPreDraw() {
+                List<View> foundViews = new ArrayList<>();
+                boolean allViewsFound = true;
+                for (String transitionName : waitForTransitionNames) {
+                    View namedView = TransitionUtils.findNamedView(to, transitionName);
+                    if (namedView != null) {
+                        foundViews.add(TransitionUtils.findNamedView(to, transitionName));
+                    } else {
+                        allViewsFound = false;
+                        break;
+                    }
+                }
+
+                if (allViewsFound && !addedSubviewListeners) {
+                    addedSubviewListeners = true;
+                    waitOnChildTransitionNames(to, foundViews, this, onTransitionPreparedListener);
+                }
+
+                return false;
+            }
+        };
+
+        to.getViewTreeObserver().addOnPreDrawListener(onPreDrawListener);
+    }
+
+    void waitOnChildTransitionNames(@NonNull final View to, @NonNull List<View> foundViews, @NonNull final OnPreDrawListener parentPreDrawListener, @NonNull final OnTransitionPreparedListener onTransitionPreparedListener) {
+        for (final View view : foundViews) {
+            OneShotPreDrawListener.add(true, view, () -> {
+                waitForTransitionNames.remove(view.getTransitionName());
+
+                removedViews.add(new ViewParentPair(view, (ViewGroup) view.getParent()));
+                ((ViewGroup) view.getParent()).removeView(view);
+
+                if (waitForTransitionNames.size() == 0) {
+                    to.getViewTreeObserver().removeOnPreDrawListener(parentPreDrawListener);
+                    to.setVisibility(View.INVISIBLE);
+                    onTransitionPreparedListener.onPrepared();
+                }
+            });
+        }
+    }
+
+    private void scheduleTargetChange(@NonNull final ViewGroup container, @Nullable final View to, @NonNull final View nonExistentView,
+                                      @NonNull final List<View> toSharedElements, @NonNull final List<View> enteringViews, @Nullable final List<View> exitingViews) {
+        OneShotPreDrawListener.add(true, container, () -> {
+            if (enterTransition != null) {
+                enterTransition.removeTarget(nonExistentView);
+                List<View> views = configureEnteringExitingViews(enterTransition, to, toSharedElements, nonExistentView);
+                enteringViews.addAll(views);
+            }
+
+            if (exitingViews != null) {
+                if (exitTransition != null) {
+                    List<View> tempExiting = new ArrayList<>();
+                    tempExiting.add(nonExistentView);
+                    TransitionUtils.replaceTargets(exitTransition, exitingViews, tempExiting);
+                }
+                exitingViews.clear();
+                exitingViews.add(nonExistentView);
+            }
+        });
+    }
+
+    private Transition mergeTransitions(boolean isPush) {
+        boolean overlap = enterTransition == null || exitTransition == null || allowTransitionOverlap(isPush);
+
+        if (overlap) {
+            return TransitionUtils.mergeTransitions(TransitionSet.ORDERING_TOGETHER, exitTransition, enterTransition, sharedElementTransition);
+        } else {
+            Transition staggered = TransitionUtils.mergeTransitions(TransitionSet.ORDERING_SEQUENTIAL, exitTransition, enterTransition);
+            return TransitionUtils.mergeTransitions(TransitionSet.ORDERING_TOGETHER, staggered, sharedElementTransition);
+        }
+    }
+
+    @NonNull List<View> configureEnteringExitingViews(@NonNull Transition transition, @Nullable View view, @NonNull List<View> sharedElements, @NonNull View nonExistentView) {
+        List<View> viewList = new ArrayList<>();
+        if (view != null) {
+            captureTransitioningViews(viewList, view);
+        }
+        viewList.removeAll(sharedElements);
+        if (!viewList.isEmpty()) {
+            viewList.add(nonExistentView);
+            TransitionUtils.addTargets(transition, viewList);
+        }
+        return viewList;
+    }
+
+    private void configureSharedElements(@NonNull ViewGroup container, @NonNull final View nonExistentView, @Nullable final View to, @Nullable View from,
+                                         final boolean isPush, @NonNull final List<View> fromSharedElements, @NonNull final List<View> toSharedElements) {
+
+        if (to == null || from == null) {
+            return;
+        }
+
+        ArrayMap<String, View> capturedFromSharedElements = captureFromSharedElements(from);
+
+        if (sharedElementNames.isEmpty()) {
+            sharedElementTransition = null;
+        } else if (capturedFromSharedElements != null) {
+            fromSharedElements.addAll(capturedFromSharedElements.values());
+        }
+
+        if (enterTransition == null && exitTransition == null && sharedElementTransition == null) {
+            return;
+        }
+
+        callSharedElementStartEnd(capturedFromSharedElements, true);
+
+        final Rect toEpicenter;
+        if (sharedElementTransition != null) {
+            toEpicenter = new Rect();
+            TransitionUtils.setTargets(sharedElementTransition, nonExistentView, fromSharedElements);
+            setFromEpicenter(capturedFromSharedElements);
+            if (enterTransition != null) {
+                enterTransition.setEpicenterCallback(new Transition.EpicenterCallback() {
+                    @Override
+                    public Rect onGetEpicenter(Transition transition) {
+                        if (toEpicenter.isEmpty()) {
+                            return null;
+                        }
+                        return toEpicenter;
+                    }
+                });
+            }
+        } else {
+            toEpicenter = null;
+        }
+
+        OneShotPreDrawListener.add(true, container, () -> {
+            ArrayMap<String, View> capturedToSharedElements = captureToSharedElements(to, isPush);
+
+            if (capturedToSharedElements != null) {
+                toSharedElements.addAll(capturedToSharedElements.values());
+                toSharedElements.add(nonExistentView);
+            }
+
+            callSharedElementStartEnd(capturedToSharedElements, false);
+            if (sharedElementTransition != null) {
+                sharedElementTransition.getTargets().clear();
+                sharedElementTransition.getTargets().addAll(toSharedElements);
+                TransitionUtils.replaceTargets(sharedElementTransition, fromSharedElements, toSharedElements);
+
+                final View toEpicenterView = getToEpicenterView(capturedToSharedElements);
+                if (toEpicenterView != null && toEpicenter != null) {
+                    TransitionUtils.getBoundsOnScreen(toEpicenterView, toEpicenter);
+                }
+            }
+        });
+    }
+
+    @Nullable View getToEpicenterView(@Nullable ArrayMap<String, View> toSharedElements) {
+        if (enterTransition != null && sharedElementNames.size() > 0 && toSharedElements != null) {
+            return toSharedElements.get(sharedElementNames.valueAt(0));
+        }
+        return null;
+    }
+
+    private void setFromEpicenter(@Nullable ArrayMap<String, View> fromSharedElements) {
+        if (sharedElementNames.size() > 0 && fromSharedElements != null) {
+            final View fromEpicenterView = fromSharedElements.get(sharedElementNames.keyAt(0));
+
+            if (sharedElementTransition != null) {
+                TransitionUtils.setEpicenter(sharedElementTransition, fromEpicenterView);
+            }
+
+            if (exitTransition != null) {
+                TransitionUtils.setEpicenter(exitTransition, fromEpicenterView);
+            }
+        }
+    }
+
+    @Nullable ArrayMap<String, View> captureToSharedElements(@Nullable final View to, boolean isPush) {
+        if (sharedElementNames.isEmpty() || sharedElementTransition == null || to == null) {
+            sharedElementNames.clear();
+            return null;
+        }
+
+        final ArrayMap<String, View> toSharedElements = new ArrayMap<>();
+        TransitionUtils.findNamedViews(toSharedElements, to);
+        for (ViewParentPair removedView : removedViews) {
+            toSharedElements.put(removedView.view.getTransitionName(), removedView.view);
+        }
+
+        final List<String> names = new ArrayList<>(sharedElementNames.values());
+
+        toSharedElements.retainAll(names);
+        if (enterTransitionCallback != null) {
+            enterTransitionCallback.onMapSharedElements(names, toSharedElements);
+            for (int i = names.size() - 1; i >= 0; i--) {
+                String name = names.get(i);
+                View view = toSharedElements.get(name);
+                if (view == null) {
+                    String key = findKeyForValue(sharedElementNames, name);
+                    if (key != null) {
+                        sharedElementNames.remove(key);
+                    }
+                } else if (!name.equals(view.getTransitionName())) {
+                    String key = findKeyForValue(sharedElementNames, name);
+                    if (key != null) {
+                        sharedElementNames.put(key, view.getTransitionName());
+                    }
+                }
+            }
+        } else {
+            for (int i = sharedElementNames.size() - 1; i >= 0; i--) {
+                final String targetName = sharedElementNames.valueAt(i);
+                if (!toSharedElements.containsKey(targetName)) {
+                    sharedElementNames.removeAt(i);
+                }
+            }
+        }
+        return toSharedElements;
+    }
+
+    @Nullable String findKeyForValue(@NonNull ArrayMap<String, String> map, @NonNull String value) {
+        final int numElements = map.size();
+        for (int i = 0; i < numElements; i++) {
+            if (value.equals(map.valueAt(i))) {
+                return map.keyAt(i);
+            }
+        }
+        return null;
+    }
+
+    @Nullable
+    private ArrayMap<String, View> captureFromSharedElements(@NonNull View from) {
+        if (sharedElementNames.isEmpty() || sharedElementTransition == null) {
+            sharedElementNames.clear();
+            return null;
+        }
+
+        final ArrayMap<String, View> fromSharedElements = new ArrayMap<>();
+        TransitionUtils.findNamedViews(fromSharedElements, from);
+
+        final List<String> names = new ArrayList<>(sharedElementNames.keySet());
+
+        fromSharedElements.retainAll(names);
+        if (exitTransitionCallback != null) {
+            exitTransitionCallback.onMapSharedElements(names, fromSharedElements);
+            for (int i = names.size() - 1; i >= 0; i--) {
+                String name = names.get(i);
+                View view = fromSharedElements.get(name);
+                if (view == null) {
+                    sharedElementNames.remove(name);
+                } else if (!name.equals(view.getTransitionName())) {
+                    String targetValue = sharedElementNames.remove(name);
+                    sharedElementNames.put(view.getTransitionName(), targetValue);
+                }
+            }
+        } else {
+            sharedElementNames.retainAll(fromSharedElements.keySet());
+        }
+        return fromSharedElements;
+    }
+
+    void callSharedElementStartEnd(@Nullable ArrayMap<String, View> sharedElements, boolean isStart) {
+        if (enterTransitionCallback != null) {
+            final int count = sharedElements == null ? 0 : sharedElements.size();
+            List<View> views = new ArrayList<>(count);
+            List<String> names = new ArrayList<>(count);
+            for (int i = 0; i < count; i++) {
+                names.add(sharedElements.keyAt(i));
+                views.add(sharedElements.valueAt(i));
+            }
+            if (isStart) {
+                enterTransitionCallback.onSharedElementStart(names, views, null);
+            } else {
+                enterTransitionCallback.onSharedElementEnd(names, views, null);
+            }
+        }
+    }
+
+    private void captureTransitioningViews(@NonNull List<View> transitioningViews, @NonNull View view) {
+        if (view.getVisibility() == View.VISIBLE) {
+            if (view instanceof ViewGroup) {
+                ViewGroup viewGroup = (ViewGroup) view;
+                if (viewGroup.isTransitionGroup()) {
+                    transitioningViews.add(viewGroup);
+                } else {
+                    int count = viewGroup.getChildCount();
+                    for (int i = 0; i < count; i++) {
+                        View child = viewGroup.getChildAt(i);
+                        captureTransitioningViews(transitioningViews, child);
+                    }
+                }
+            } else {
+                transitioningViews.add(view);
+            }
+        }
+    }
+
+    private void scheduleRemoveTargets(@NonNull final Transition overallTransition,
+                                       @Nullable final Transition enterTransition, @Nullable final List<View> enteringViews,
+                                       @Nullable final Transition exitTransition, @Nullable final List<View> exitingViews,
+                                       @Nullable final Transition sharedElementTransition, @Nullable final List<View> toSharedElements) {
+        overallTransition.addListener(new TransitionListener() {
+            @Override
+            public void onTransitionStart(Transition transition) {
+                if (enterTransition != null && enteringViews != null) {
+                    TransitionUtils.replaceTargets(enterTransition, enteringViews, null);
+                }
+                if (exitTransition != null && exitingViews != null) {
+                    TransitionUtils.replaceTargets(exitTransition, exitingViews, null);
+                }
+                if (sharedElementTransition != null && toSharedElements != null) {
+                    TransitionUtils.replaceTargets(sharedElementTransition, toSharedElements, null);
+                }
+            }
+
+            @Override
+            public void onTransitionEnd(Transition transition) { }
+
+            @Override
+            public void onTransitionCancel(Transition transition) { }
+
+            @Override
+            public void onTransitionPause(Transition transition) { }
+
+            @Override
+            public void onTransitionResume(Transition transition) { }
+        });
+    }
+
+    private void setNameOverrides(@NonNull final View container, @NonNull final List<View> toSharedElements) {
+        OneShotPreDrawListener.add(true, container, () -> {
+            final int numSharedElements = toSharedElements.size();
+            for (int i = 0; i < numSharedElements; i++) {
+                View view = toSharedElements.get(i);
+                String name = view.getTransitionName();
+                if (name != null) {
+                    String inName = findKeyForValue(sharedElementNames, name);
+                    view.setTransitionName(inName);
+                }
+            }
+        });
+    }
+
+    private void scheduleNameReset(@NonNull final ViewGroup container, @NonNull final List<View> toSharedElements) {
+        OneShotPreDrawListener.add(true, container, () -> {
+            final int numSharedElements = toSharedElements.size();
+            for (int i = 0; i < numSharedElements; i++) {
+                final View view = toSharedElements.get(i);
+                final String name = view.getTransitionName();
+                final String inName = sharedElementNames.get(name);
+                view.setTransitionName(inName);
+            }
+        });
+    }
+
+    /**
+     * Will be called when views are ready to have their shared elements configured. Within this method one of the addSharedElement methods
+     * should be called for each shared element that will be used. If one or more of these shared elements will not instantly be available in
+     * the incoming view (for ex, in a RecyclerView), waitOnSharedElementNamed can be called to delay the transition until everything is available.
+     */
+    public abstract void configureSharedElements(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return the transition that will be used on the exiting ("from") view, if one is desired.
+     */
+    @Nullable
+    public abstract Transition getExitTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return the transition that will be used on shared elements between the from and to views.
+     */
+    @Nullable
+    public abstract Transition getSharedElementTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return the transition that will be used on the entering ("to") view, if one is desired.
+     */
+    @Nullable
+    public abstract Transition getEnterTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    /**
+     * Should return a callback that can be used to customize transition behavior of the shared element transition for the "from" view.
+     */
+    @Nullable
+    public SharedElementCallback getExitTransitionCallback(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush) {
+        return null;
+    }
+
+    /**
+     * Should return a callback that can be used to customize transition behavior of the shared element transition for the "to" view.
+     */
+    @Nullable
+    public SharedElementCallback getEnterTransitionCallback(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush) {
+        return null;
+    }
+
+    /**
+     * Should return whether or not the the exit transition and enter transition should overlap. If true,
+     * the enter transition will start as soon as possible. Otherwise, the enter transition will wait until the
+     * completion of the exit transition. Defaults to true.
+     */
+    public boolean allowTransitionOverlap(boolean isPush) {
+        return true;
+    }
+
+    /**
+     * Used to register an element that will take part in the shared element transition.
+     *
+     * @param name The transition name that is used for both the entering and exiting views.
+     */
+    protected final void addSharedElement(@NonNull String name) {
+        sharedElementNames.put(name, name);
+    }
+
+    /**
+     * Used to register an element that will take part in the shared element transition. Maps the name used in the
+     * "from" view to the name used in the "to" view if they are not the same.
+     *
+     * @param fromName The transition name used in the "from" view
+     * @param toName The transition name used in the "to" view
+     */
+    protected final void addSharedElement(@NonNull String fromName, @NonNull String toName) {
+        sharedElementNames.put(fromName, toName);
+    }
+
+    /**
+     * Used to register an element that will take part in the shared element transition. Maps the name used in the
+     * "from" view to the name used in the "to" view if they are not the same.
+     *
+     * @param sharedElement The view from the "from" view that will take part in the shared element transition
+     * @param toName The transition name used in the "to" view
+     */
+    protected final void addSharedElement(@NonNull View sharedElement, @NonNull String toName) {
+        String transitionName = sharedElement.getTransitionName();
+        if (transitionName == null) {
+            throw new IllegalArgumentException("Unique transitionNames are required for all sharedElements");
+        }
+        sharedElementNames.put(transitionName, toName);
+    }
+
+    /**
+     * The transition will be delayed until the view with the name passed in is available in the "to" hierarchy. This is
+     * particularly useful for views that don't load instantly, like RecyclerViews. Note that using this method can
+     * potentially lock up your app indefinitely if the view never loads!
+     */
+    protected final void waitOnSharedElementNamed(@NonNull String name) {
+        if (!sharedElementNames.values().contains(name)) {
+            throw new IllegalStateException("Can't wait on a shared element that hasn't been registered using addSharedElement");
+        }
+        waitForTransitionNames.add(name);
+    }
+
+    private static class OneShotPreDrawListener implements OnPreDrawListener, View.OnAttachStateChangeListener {
+
+        private final View view;
+        private ViewTreeObserver viewTreeObserver;
+        private final Runnable runnable;
+        private final boolean preDrawReturnValue;
+
+        private OneShotPreDrawListener(boolean preDrawReturnValue, @NonNull View view, @NonNull Runnable runnable) {
+            this.preDrawReturnValue = preDrawReturnValue;
+            this.view = view;
+            viewTreeObserver = view.getViewTreeObserver();
+            this.runnable = runnable;
+        }
+
+        @NonNull
+        public static OneShotPreDrawListener add(boolean preDrawReturnValue, @NonNull View view, @NonNull Runnable runnable) {
+            OneShotPreDrawListener listener = new OneShotPreDrawListener(preDrawReturnValue, view, runnable);
+            view.getViewTreeObserver().addOnPreDrawListener(listener);
+            view.addOnAttachStateChangeListener(listener);
+            return listener;
+        }
+
+        @Override
+        public boolean onPreDraw() {
+            removeListener();
+            runnable.run();
+            return preDrawReturnValue;
+        }
+
+        private void removeListener() {
+            if (viewTreeObserver.isAlive()) {
+                viewTreeObserver.removeOnPreDrawListener(this);
+            } else {
+                view.getViewTreeObserver().removeOnPreDrawListener(this);
+            }
+            view.removeOnAttachStateChangeListener(this);
+        }
+
+        @Override
+        public void onViewAttachedToWindow(View v) {
+            viewTreeObserver = v.getViewTreeObserver();
+        }
+
+        @Override
+        public void onViewDetachedFromWindow(View v) {
+            removeListener();
+        }
+
+    }
+
+    private static class ViewParentPair {
+        @NonNull final View view;
+        @NonNull final ViewGroup parent;
+
+        ViewParentPair(@NonNull View view, ViewGroup parent) {
+            this.view = view;
+            this.parent = parent;
+        }
+    }
+
+}
@@ -0,0 +1,149 @@
+package com.bluelinelabs.conductor.changehandler.platformtransition;
+
+import android.annotation.TargetApi;
+import android.os.Build;
+import android.transition.Transition;
+import android.transition.Transition.TransitionListener;
+import android.transition.TransitionManager;
+import android.view.View;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import com.bluelinelabs.conductor.Controller;
+import com.bluelinelabs.conductor.ControllerChangeHandler;
+
+/**
+ * A base {@link ControllerChangeHandler} that facilitates using {@link Transition}s to replace Controller Views.
+ * <p/>
+ * Note that this class uses Android's <b>platform</b> {@link Transition}. If you're using androidx transitions, consider
+ * using the {@code TransitionChangeHandler} provided by the {@code androidx-transitions} Conductor module.
+ */
+@TargetApi(Build.VERSION_CODES.LOLLIPOP)
+public abstract class TransitionChangeHandler extends ControllerChangeHandler {
+
+    public interface OnTransitionPreparedListener {
+        void onPrepared();
+    }
+
+    boolean canceled;
+    private boolean needsImmediateCompletion;
+
+    /**
+     * Should be overridden to return the Transition to use while replacing Views.
+     *
+     * @param container The container these Views are hosted in
+     * @param from      The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to        The next View that should be put in the container or {@code null} if no Controller is being transitioned to
+     * @param isPush    True if this is a push transaction, false if it's a pop
+     */
+    @NonNull
+    protected abstract Transition getTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush);
+
+    @Override
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
+        super.onAbortPush(newHandler, newTop);
+
+        canceled = true;
+    }
+
+    @Override
+    public void completeImmediately() {
+        super.completeImmediately();
+
+        needsImmediateCompletion = true;
+    }
+
+    @Nullable
+    private ControllerChangeCompletedListener listener;
+
+    @Override
+    public void performChange(@NonNull final ViewGroup container, @Nullable final View from, @Nullable final View to, final boolean isPush, @NonNull final ControllerChangeCompletedListener changeListener) {
+        listener = changeListener;
+        if (canceled) {
+            changeListener.onChangeCompleted();
+            return;
+        }
+        if (needsImmediateCompletion) {
+            executePropertyChanges(container, from, to, null, isPush);
+            changeListener.onChangeCompleted();
+            return;
+        }
+
+        final Runnable onTransitionNotStarted = changeListener::onChangeCompleted;
+
+        final Transition transition = getTransition(container, from, to, isPush);
+        transition.addListener(new TransitionListener() {
+            @Override
+            public void onTransitionStart(Transition transition) {
+                container.removeCallbacks(onTransitionNotStarted);
+            }
+
+            @Override
+            public void onTransitionEnd(Transition transition) {
+                listener.onChangeCompleted();
+                listener = null;
+            }
+
+            @Override
+            public void onTransitionCancel(Transition transition) {
+                listener.onChangeCompleted();
+                listener = null;
+            }
+
+            @Override
+            public void onTransitionPause(Transition transition) { }
+
+            @Override
+            public void onTransitionResume(Transition transition) { }
+        });
+
+        prepareForTransition(container, from, to, transition, isPush, () -> {
+            if (!canceled) {
+                TransitionManager.beginDelayedTransition(container, transition);
+                executePropertyChanges(container, from, to, transition, isPush);
+                container.post(onTransitionNotStarted);
+            }
+        });
+    }
+
+    @Override
+    public boolean removesFromViewOnPush() {
+        return true;
+    }
+
+    /**
+     * Called before a transition occurs. This can be used to reorder views, set their transition names, etc. The transition will begin
+     * when {@code onTransitionPreparedListener} is called.
+     *
+     * @param container  The container these Views are hosted in
+     * @param from       The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to         The next View that should be put in the container or {@code null} if no Controller is being transitioned to
+     * @param transition The transition that is being prepared for
+     * @param isPush     True if this is a push transaction, false if it's a pop
+     */
+    public void prepareForTransition(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, @NonNull Transition transition, boolean isPush, @NonNull OnTransitionPreparedListener onTransitionPreparedListener) {
+        onTransitionPreparedListener.onPrepared();
+    }
+
+    /**
+     * This should set all view properties needed for the transition to work properly. By default it removes the "from" view
+     * and adds the "to" view.
+     *
+     * @param container  The container these Views are hosted in
+     * @param from       The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to         The next View that should be put in the container or {@code null} if no Controller is being transitioned to
+     * @param transition The transition with which {@code TransitionManager.beginDelayedTransition} has been called. This will be null only if another ControllerChangeHandler immediately overrides this one.
+     * @param isPush     True if this is a push transaction, false if it's a pop
+     */
+    public void executePropertyChanges(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, @Nullable Transition transition, boolean isPush) {
+        if (from != null && (removesFromViewOnPush() || !isPush) && from.getParent() == container) {
+            container.removeView(from);
+        }
+        if (to != null && to.getParent() == null) {
+            container.addView(to);
+        }
+    }
+
+}
@@ -0,0 +1,184 @@
+package com.bluelinelabs.conductor.internal;
+
+import android.annotation.TargetApi;
+import android.graphics.Rect;
+import android.os.Build;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import android.transition.Transition;
+import android.transition.TransitionSet;
+import android.view.View;
+import android.view.ViewGroup;
+
+import java.util.List;
+import java.util.Map;
+
+@TargetApi(Build.VERSION_CODES.LOLLIPOP)
+public class TransitionUtils {
+
+    public static void findNamedViews(@NonNull Map<String, View> namedViews, View view) {
+        if (view.getVisibility() == View.VISIBLE) {
+            String transitionName = view.getTransitionName();
+            if (transitionName != null) {
+                namedViews.put(transitionName, view);
+            }
+
+            if (view instanceof ViewGroup) {
+                ViewGroup viewGroup = (ViewGroup) view;
+                int childCount = viewGroup.getChildCount();
+                for (int i = 0; i < childCount; i++) {
+                    View child = viewGroup.getChildAt(i);
+                    findNamedViews(namedViews, child);
+                }
+            }
+        }
+    }
+
+    @Nullable
+    public static View findNamedView(@NonNull View view, @NonNull String transitionName) {
+        if (transitionName.equals(view.getTransitionName())) {
+            return view;
+        }
+
+        if (view instanceof ViewGroup) {
+            ViewGroup viewGroup = (ViewGroup) view;
+            int childCount = viewGroup.getChildCount();
+            for (int i = 0; i < childCount; i++) {
+                View viewWithTransitionName = findNamedView(viewGroup.getChildAt(i), transitionName);
+                if (viewWithTransitionName != null) {
+                    return viewWithTransitionName;
+                }
+            }
+        }
+
+        return null;
+    }
+
+    public static void setEpicenter(@NonNull Transition transition, @Nullable View view) {
+        if (view != null) {
+            final Rect epicenter = new Rect();
+            getBoundsOnScreen(view, epicenter);
+            transition.setEpicenterCallback(new Transition.EpicenterCallback() {
+                @Override
+                public Rect onGetEpicenter(Transition transition) {
+                    return epicenter;
+                }
+            });
+        }
+    }
+
+    public static void getBoundsOnScreen(@NonNull View view, @NonNull Rect epicenter) {
+        int[] loc = new int[2];
+        view.getLocationOnScreen(loc);
+        epicenter.set(loc[0], loc[1], loc[0] + view.getWidth(), loc[1] + view.getHeight());
+    }
+
+    public static void setTargets(@NonNull Transition transition, @NonNull View nonExistentView, @NonNull List<View> sharedViews) {
+        final List<View> views = transition.getTargets();
+        views.clear();
+        final int count = sharedViews.size();
+        for (int i = 0; i < count; i++) {
+            final View view = sharedViews.get(i);
+            bfsAddViewChildren(views, view);
+        }
+        views.add(nonExistentView);
+        sharedViews.add(nonExistentView);
+        addTargets(transition, sharedViews);
+    }
+
+    public static void addTargets(@Nullable Transition transition, @NonNull List<View> views) {
+        if (transition == null) {
+            return;
+        }
+        if (transition instanceof TransitionSet) {
+            TransitionSet set = (TransitionSet) transition;
+            int numTransitions = set.getTransitionCount();
+            for (int i = 0; i < numTransitions; i++) {
+                Transition child = set.getTransitionAt(i);
+                addTargets(child, views);
+            }
+        } else if (!hasSimpleTarget(transition)) {
+            List<View> targets = transition.getTargets();
+            if (isNullOrEmpty(targets)) {
+                int numViews = views.size();
+                for (int i = 0; i < numViews; i++) {
+                    transition.addTarget(views.get(i));
+                }
+            }
+        }
+    }
+
+    public static void replaceTargets(@NonNull Transition transition, @NonNull List<View> oldTargets, @Nullable List<View> newTargets) {
+        if (transition instanceof TransitionSet) {
+            TransitionSet set = (TransitionSet) transition;
+            int numTransitions = set.getTransitionCount();
+            for (int i = 0; i < numTransitions; i++) {
+                Transition child = set.getTransitionAt(i);
+                replaceTargets(child, oldTargets, newTargets);
+            }
+        } else if (!hasSimpleTarget(transition)) {
+            List<View> targets = transition.getTargets();
+            if (targets != null && targets.size() == oldTargets.size() && targets.containsAll(oldTargets)) {
+                final int targetCount = newTargets == null ? 0 : newTargets.size();
+                for (int i = 0; i < targetCount; i++) {
+                    transition.addTarget(newTargets.get(i));
+                }
+                for (int i = oldTargets.size() - 1; i >= 0; i--) {
+                    transition.removeTarget(oldTargets.get(i));
+                }
+            }
+        }
+    }
+
+    private static void bfsAddViewChildren(@NonNull final List<View> views, @NonNull final View startView) {
+        final int startIndex = views.size();
+        if (containedBeforeIndex(views, startView, startIndex)) {
+            return; // This child is already in the list, so all its children are also.
+        }
+        views.add(startView);
+        for (int index = startIndex; index < views.size(); index++) {
+            final View view = views.get(index);
+            if (view instanceof ViewGroup) {
+                ViewGroup viewGroup = (ViewGroup) view;
+                final int childCount = viewGroup.getChildCount();
+                for (int childIndex = 0; childIndex < childCount; childIndex++) {
+                    final View child = viewGroup.getChildAt(childIndex);
+                    if (!containedBeforeIndex(views, child, startIndex)) {
+                        views.add(child);
+                    }
+                }
+            }
+        }
+    }
+
+    private static boolean containedBeforeIndex(@NonNull List<View> views, View view, int maxIndex) {
+        for (int i = 0; i < maxIndex; i++) {
+            if (views.get(i) == view) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    public static boolean hasSimpleTarget(@NonNull Transition transition) {
+        return !isNullOrEmpty(transition.getTargetIds())
+                || !isNullOrEmpty(transition.getTargetNames())
+                || !isNullOrEmpty(transition.getTargetTypes());
+    }
+
+    private static boolean isNullOrEmpty(@Nullable List list) {
+        return list == null || list.isEmpty();
+    }
+
+    @NonNull
+    public static TransitionSet mergeTransitions(int ordering, Transition... transitions) {
+        TransitionSet transitionSet = new TransitionSet();
+        for (Transition transition : transitions) {
+            if (transition != null) {
+                transitionSet.addTransition(transition);
+            }
+        }
+        transitionSet.setOrdering(ordering);
+        return transitionSet;
+    }
+}
@@ -0,0 +1,26 @@
+apply plugin: 'com.android.library'
+apply plugin: 'kotlin-android'
+
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode Integer.parseInt(project.VERSION_CODE)
+        versionName project.VERSION_NAME
+    }
+}
+
+dependencies {
+    testImplementation rootProject.ext.junit
+    testImplementation rootProject.ext.roboelectric
+
+    implementation rootProject.ext.androidxAppCompat
+    implementation project(':conductor')
+}
+
+ext.artifactId = 'conductor-viewpager'
+
+apply from: rootProject.file('dependencies.gradle')
+apply plugin: "com.vanniktech.maven.publish"
@@ -0,0 +1,3 @@
+POM_NAME=Conductor PagerAdapter
+POM_ARTIFACT_ID=conductor-viewpager
+POM_PACKAGING=aar
@@ -0,0 +1,3 @@
+<manifest package="com.bluelinelabs.conductor.viewpager">
+    <application />
+</manifest>
@@ -0,0 +1,210 @@
+package com.bluelinelabs.conductor.viewpager;
+
+import android.os.Bundle;
+import android.os.Parcelable;
+import android.util.SparseArray;
+import android.view.View;
+import android.view.ViewGroup;
+
+import com.bluelinelabs.conductor.Controller;
+import com.bluelinelabs.conductor.Router;
+import com.bluelinelabs.conductor.RouterTransaction;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.viewpager.widget.PagerAdapter;
+
+/**
+ * An adapter for ViewPagers that uses Routers as pages
+ */
+public abstract class RouterPagerAdapter extends PagerAdapter {
+
+    private static final String KEY_SAVED_PAGES = "RouterPagerAdapter.savedStates";
+    private static final String KEY_TAGS_KEYS = "RouterPagerAdapter.tags.keys";
+    private static final String KEY_TAGS_VALUES = "RouterPagerAdapter.tags.values";
+    private static final String KEY_MAX_PAGES_TO_STATE_SAVE = "RouterPagerAdapter.maxPagesToStateSave";
+    private static final String KEY_SAVE_PAGE_HISTORY = "RouterPagerAdapter.savedPageHistory";
+
+    private final Controller host;
+    private int maxPagesToStateSave = Integer.MAX_VALUE;
+    private Map<Integer, String> tags = new HashMap<>();
+    private SparseArray<Bundle> savedPages = new SparseArray<>();
+    private SparseArray<Router> visibleRouters = new SparseArray<>();
+    private ArrayList<Integer> savedPageHistory = new ArrayList<>();
+    private Router currentPrimaryRouter;
+
+    /**
+     * Creates a new RouterPagerAdapter using the passed host.
+     */
+    public RouterPagerAdapter(@NonNull Controller host) {
+        this.host = host;
+    }
+
+    /**
+     * Called when a router is instantiated. Here the router's root should be set if needed.
+     *
+     * @param router   The router used for the page
+     * @param position The page position to be instantiated.
+     */
+    public abstract void configureRouter(@NonNull Router router, int position);
+
+    /**
+     * Sets the maximum number of pages that will have their states saved. When this number is exceeded,
+     * the page that was state saved least recently will have its state removed from the save data.
+     */
+    public void setMaxPagesToStateSave(int maxPagesToStateSave) {
+        if (maxPagesToStateSave < 0) {
+            throw new IllegalArgumentException("Only positive integers may be passed for maxPagesToStateSave.");
+        }
+
+        this.maxPagesToStateSave = maxPagesToStateSave;
+
+        ensurePagesSaved();
+    }
+
+    @Override
+    public Object instantiateItem(ViewGroup container, int position) {
+        final String name = makeRouterName(container.getId(), getItemId(position));
+
+        // Ensure we don't try to restore state for a router with a different ID just because
+        // the position was reused. Fixes https://github.com/bluelinelabs/Conductor/issues/582
+        if (tags.get(position) != null && !tags.get(position).equals(name)) {
+            savedPages.remove(position);
+        }
+
+        Router router = host.getChildRouter(container, name);
+        if (!router.hasRootController()) {
+            Bundle routerSavedState = savedPages.get(position);
+
+            if (routerSavedState != null) {
+                router.restoreInstanceState(routerSavedState);
+                savedPages.remove(position);
+                savedPageHistory.remove((Integer) position);
+            }
+        }
+
+        router.rebindIfNeeded();
+        configureRouter(router, position);
+
+        if (router != currentPrimaryRouter) {
+            for (RouterTransaction transaction : router.getBackstack()) {
+                transaction.controller().setOptionsMenuHidden(true);
+            }
+        }
+
+        tags.put(position, name);
+        visibleRouters.put(position, router);
+        return router;
+    }
+
+    @Override
+    public void destroyItem(ViewGroup container, int position, Object object) {
+        Router router = (Router)object;
+
+        Bundle savedState = new Bundle();
+        router.saveInstanceState(savedState);
+        savedPages.put(position, savedState);
+
+        savedPageHistory.remove((Integer) position);
+        savedPageHistory.add(position);
+
+        ensurePagesSaved();
+
+        host.removeChildRouter(router);
+
+        visibleRouters.remove(position);
+    }
+
+    @Override
+    public void setPrimaryItem(ViewGroup container, int position, Object object) {
+        Router router = (Router)object;
+        if (router != currentPrimaryRouter) {
+            if (currentPrimaryRouter != null) {
+                for (RouterTransaction transaction : currentPrimaryRouter.getBackstack()) {
+                    transaction.controller().setOptionsMenuHidden(true);
+                }
+            }
+            if (router != null) {
+                for (RouterTransaction transaction : router.getBackstack()) {
+                    transaction.controller().setOptionsMenuHidden(false);
+                }
+            }
+            currentPrimaryRouter = router;
+        }
+    }
+
+    @Override
+    public boolean isViewFromObject(View view, Object object) {
+        Router router = (Router)object;
+        final List<RouterTransaction> backstack = router.getBackstack();
+        for (RouterTransaction transaction : backstack) {
+            if (transaction.controller().getView() == view) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    @Override
+    public Parcelable saveState() {
+        Bundle bundle = new Bundle();
+        bundle.putSparseParcelableArray(KEY_SAVED_PAGES, savedPages);
+        bundle.putIntegerArrayList(KEY_TAGS_KEYS, new ArrayList<>(tags.keySet()));
+        bundle.putStringArrayList(KEY_TAGS_VALUES, new ArrayList<>(tags.values()));
+        bundle.putInt(KEY_MAX_PAGES_TO_STATE_SAVE, maxPagesToStateSave);
+        bundle.putIntegerArrayList(KEY_SAVE_PAGE_HISTORY, savedPageHistory);
+        return bundle;
+    }
+
+    @Override
+    public void restoreState(Parcelable state, ClassLoader loader) {
+        Bundle bundle = (Bundle)state;
+        if (state != null) {
+            savedPages = bundle.getSparseParcelableArray(KEY_SAVED_PAGES);
+            maxPagesToStateSave = bundle.getInt(KEY_MAX_PAGES_TO_STATE_SAVE);
+            savedPageHistory = bundle.getIntegerArrayList(KEY_SAVE_PAGE_HISTORY);
+
+            List<Integer> tagsKeys = bundle.getIntegerArrayList(KEY_TAGS_KEYS);
+            List<String> tagsValues = bundle.getStringArrayList(KEY_TAGS_VALUES);
+            if (tagsKeys != null && tagsValues != null && tagsKeys.size() == tagsValues.size()) {
+                for (int i = 0; i < tagsKeys.size(); i++) {
+                    tags.put(tagsKeys.get(i), tagsValues.get(i));
+                }
+            }
+        }
+    }
+
+    /**
+     * Returns the already instantiated Router in the specified position or {@code null} if there
+     * is no router associated with this position.
+     */
+    @Nullable
+    public Router getRouter(int position) {
+        return visibleRouters.get(position);
+    }
+
+    public long getItemId(int position) {
+        return position;
+    }
+
+    SparseArray<Bundle> getSavedPages() {
+        return savedPages;
+    }
+
+    private void ensurePagesSaved() {
+        while (savedPages.size() > maxPagesToStateSave) {
+            int positionToRemove = savedPageHistory.remove(0);
+            savedPages.remove(positionToRemove);
+        }
+    }
+
+    private static String makeRouterName(int viewId, long id) {
+        return viewId + ":" + id;
+    }
+
+}
@@ -0,0 +1,104 @@
+package com.bluelinelabs.conductor.viewpager
+
+import android.app.Activity
+import android.widget.FrameLayout
+import androidx.core.view.ViewCompat
+import com.bluelinelabs.conductor.Conductor
+import com.bluelinelabs.conductor.Router
+import com.bluelinelabs.conductor.RouterTransaction.Companion.with
+import com.bluelinelabs.conductor.viewpager.util.FakePager
+import com.bluelinelabs.conductor.viewpager.util.TestController
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.Robolectric
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.Config
+
+@RunWith(RobolectricTestRunner::class)
+@Config(manifest = Config.NONE)
+class StateSaveTests {
+
+  private val pager: FakePager
+  private val pagerAdapter: RouterPagerAdapter
+
+  init {
+    val activityController = Robolectric.buildActivity(Activity::class.java).setup()
+    val router = Conductor.attachRouter(activityController.get(), FrameLayout(activityController.get()), null)
+    val controller = TestController()
+    router.setRoot(with(controller))
+    pager = FakePager(FrameLayout(activityController.get()).also {
+      it.id = ViewCompat.generateViewId()
+    })
+    pager.offscreenPageLimit = 1
+    pagerAdapter = object : RouterPagerAdapter(controller) {
+      override fun configureRouter(router: Router, position: Int) {
+        if (!router.hasRootController()) {
+          router.setRoot(with(TestController()))
+        }
+      }
+
+      override fun getCount(): Int {
+        return 20
+      }
+    }
+    pager.setAdapter(pagerAdapter)
+  }
+
+  @Test
+  fun testNoMaxSaves() {
+    // Load all pages
+    for (i in 0 until pagerAdapter.count) {
+      pager.pageTo(i)
+    }
+    pager.pageTo(pagerAdapter.count / 2)
+
+    // Ensure all non-visible pages are saved
+    assertEquals(
+      pagerAdapter.count - 1 - (pager.offscreenPageLimit * 2),
+      pagerAdapter.savedPages.size()
+    )
+  }
+
+  @Test
+  fun testMaxSavedSet() {
+    val maxPages = 3
+    pagerAdapter.setMaxPagesToStateSave(maxPages)
+
+    // Load all pages
+    for (i in 0 until pagerAdapter.count) {
+      pager.pageTo(i)
+    }
+    val firstSelectedItem = pagerAdapter.count / 2
+    pager.pageTo(firstSelectedItem)
+    var savedPages = pagerAdapter.savedPages
+
+    // Ensure correct number of pages are saved
+    assertEquals(maxPages, savedPages.size())
+
+    // Ensure correct pages are saved
+    assertEquals(
+      pagerAdapter.count - 3,
+      savedPages.keyAt(0)
+    )
+    assertEquals(
+      pagerAdapter.count - 2,
+      savedPages.keyAt(1)
+    )
+    assertEquals(
+      pagerAdapter.count - 1,
+      savedPages.keyAt(2)
+    )
+    val secondSelectedItem = 1
+    pager.pageTo(secondSelectedItem)
+    savedPages = pagerAdapter.savedPages
+
+    // Ensure correct number of pages are saved
+    assertEquals(maxPages, savedPages.size())
+
+    // Ensure correct pages are saved
+    assertEquals(firstSelectedItem - 1, savedPages.keyAt(0))
+    assertEquals(firstSelectedItem, savedPages.keyAt(1))
+    assertEquals(firstSelectedItem + 1, savedPages.keyAt(2))
+  }
+}
@@ -0,0 +1,61 @@
+package com.bluelinelabs.conductor.viewpager.util;
+
+import android.util.SparseArray;
+import android.view.ViewGroup;
+
+import com.bluelinelabs.conductor.viewpager.RouterPagerAdapter;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class FakePager {
+
+    private ViewGroup container;
+    private int offscreenPageLimit;
+    private final SparseArray<Object> pages = new SparseArray<>();
+
+    private RouterPagerAdapter adapter;
+
+    public FakePager(ViewGroup container) {
+        this.container = container;
+    }
+
+    public void setAdapter(RouterPagerAdapter adapter) {
+        this.adapter = adapter;
+    }
+
+    public void pageTo(int page) {
+        int firstPage = Math.max(0, page - offscreenPageLimit);
+        int lastPage = Math.min(adapter.getCount() - 1, page + offscreenPageLimit);
+
+        List<Integer> pagesI = new ArrayList<>();
+        for (int i = 0; i < pages.size(); i++) {
+            pagesI.add(pages.keyAt(i));
+        }
+
+        for (int i = pages.size() - 1; i >= 0; i--) {
+            int key = pages.keyAt(i);
+
+            if (key < firstPage || key > lastPage) {
+                adapter.destroyItem(container, key, pages.get(key));
+                pages.remove(key);
+            }
+        }
+
+        for (int key = firstPage; key <= lastPage; key++) {
+            if (pages.get(key) == null) {
+                pages.put(key, adapter.instantiateItem(container, key));
+            }
+        }
+
+        adapter.setPrimaryItem(container, page, pages.get(page));
+    }
+
+    public int getOffscreenPageLimit() {
+        return offscreenPageLimit;
+    }
+
+    public void setOffscreenPageLimit(int offscreenPageLimit) {
+        this.offscreenPageLimit = offscreenPageLimit;
+    }
+}
@@ -0,0 +1,21 @@
+package com.bluelinelabs.conductor.viewpager.util;
+
+import android.os.Bundle;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.FrameLayout;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import com.bluelinelabs.conductor.Controller;
+
+public class TestController extends Controller {
+
+    @Override @NonNull
+    protected View onCreateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container, @Nullable Bundle savedViewState) {
+        return new FrameLayout(inflater.getContext());
+    }
+
+}
@@ -1,37 +0,0 @@
-apply from: rootProject.file('dependencies.gradle')
-apply from: rootProject.file('gradle-mvn-push.gradle')
-
-apply plugin: 'com.android.library'
-
-android {
-    compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
-
-    lintOptions {
-        abortOnError false
-    }
-
-    compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_7
-        targetCompatibility JavaVersion.VERSION_1_7
-    }
-
-    defaultConfig {
-        minSdkVersion rootProject.ext.minSdkVersion
-        targetSdkVersion rootProject.ext.targetSdkVersion
-        versionCode Integer.parseInt(project.VERSION_CODE)
-        versionName project.VERSION_NAME
-    }
-}
-
-dependencies {
-    compile rootProject.ext.rxJava
-    compile rootProject.ext.rxAndroid
-    compile rootProject.ext.rxLifecycle
-    compile rootProject.ext.rxLifecycleAndroid
-
-    compile project(':conductor')
-}
-
-ext.artifactId = 'conductor-rxlifecycle'
-
@@ -1,3 +0,0 @@
-POM_NAME=Conductor RxLifecycle Extensions
-POM_ARTIFACT_ID=conductor-rxlifecycle
-POM_PACKAGING=aar
@@ -1,3 +0,0 @@
-<manifest package="com.bluelinelabs.conductor.rxlifecycle">
-    <application />
-</manifest>
@@ -1,52 +0,0 @@
-package com.bluelinelabs.conductor.rxlifecycle;
-
-import android.support.annotation.NonNull;
-import android.view.View;
-
-import com.bluelinelabs.conductor.Controller;
-import com.bluelinelabs.conductor.Controller.LifecycleListener;
-
-import rx.subjects.BehaviorSubject;
-
-/**
- * A simple utility class that will create a {@link BehaviorSubject} that calls onNext when events
- * occur in your {@link Controller}
- */
-public class ControllerLifecycleSubjectHelper {
-
-    private ControllerLifecycleSubjectHelper() { }
-
-    public static BehaviorSubject<ControllerEvent> create(Controller controller) {
-        final BehaviorSubject<ControllerEvent> subject = BehaviorSubject.create(ControllerEvent.CREATE);
-
-        controller.addLifecycleListener(new LifecycleListener() {
-            @Override
-            public void preCreateView(@NonNull Controller controller) {
-                subject.onNext(ControllerEvent.CREATE_VIEW);
-            }
-
-            @Override
-            public void preAttach(@NonNull Controller controller, @NonNull View view) {
-                subject.onNext(ControllerEvent.ATTACH);
-            }
-
-            @Override
-            public void preDetach(@NonNull Controller controller, @NonNull View view) {
-                subject.onNext(ControllerEvent.DETACH);
-            }
-
-            @Override
-            public void preDestroyView(@NonNull Controller controller, @NonNull View view) {
-                subject.onNext(ControllerEvent.DESTROY_VIEW);
-            }
-
-            @Override
-            public void preDestroy(@NonNull Controller controller) {
-                subject.onNext(ControllerEvent.DESTROY);
-            }
-        });
-
-        return subject;
-    }
-
-}
@@ -1,46 +0,0 @@
-package com.bluelinelabs.conductor.rxlifecycle;
-
-import android.support.annotation.CheckResult;
-import android.support.annotation.NonNull;
-
-import com.trello.rxlifecycle.LifecycleTransformer;
-import com.trello.rxlifecycle.OutsideLifecycleException;
-import com.trello.rxlifecycle.RxLifecycle;
-
-import rx.Observable;
-import rx.functions.Func1;
-
-public class RxControllerLifecycle {
-
-    /**
-     * Binds the given source to a Controller lifecycle. This is the Controller version of
-     * {@link com.trello.rxlifecycle.android.RxLifecycleAndroid#bindFragment(Observable)}.
-     *
-     * @param lifecycle the lifecycle sequence of a Controller
-     * @return a reusable {@link Observable.Transformer} that unsubscribes the source during the Controller lifecycle
-     */
-    @NonNull
-    @CheckResult
-    public static <T> LifecycleTransformer<T> bindController(@NonNull final Observable<ControllerEvent> lifecycle) {
-        return RxLifecycle.bind(lifecycle, CONTROLLER_LIFECYCLE);
-    }
-
-    private static final Func1<ControllerEvent, ControllerEvent> CONTROLLER_LIFECYCLE =
-            new Func1<ControllerEvent, ControllerEvent>() {
-                @Override
-                public ControllerEvent call(ControllerEvent lastEvent) {
-                    switch (lastEvent) {
-                        case CREATE:
-                            return ControllerEvent.DESTROY;
-                        case ATTACH:
-                            return ControllerEvent.DETACH;
-                        case CREATE_VIEW:
-                            return ControllerEvent.DESTROY_VIEW;
-                        case DETACH:
-                            return ControllerEvent.DESTROY;
-                        default:
-                            throw new OutsideLifecycleException("Cannot bind to Controller lifecycle when outside of it.");
-                    }
-                }
-            };
-}
@@ -1,3 +0,0 @@
-POM_NAME=Conductor Support Extensions
-POM_ARTIFACT_ID=conductor-support
-POM_PACKAGING=aar
@@ -1,3 +0,0 @@
-<manifest package="com.bluelinelabs.conductor.support">
-    <application />
-</manifest>
@@ -1,105 +0,0 @@
-package com.bluelinelabs.conductor.support;
-
-import android.os.Bundle;
-import android.os.Parcelable;
-import android.support.v4.view.PagerAdapter;
-import android.util.SparseArray;
-import android.view.View;
-import android.view.ViewGroup;
-
-import com.bluelinelabs.conductor.Controller;
-import com.bluelinelabs.conductor.Router;
-import com.bluelinelabs.conductor.RouterTransaction;
-
-/**
- * An adapter for ViewPagers that will handle adding and removing Controllers
- */
-public abstract class ControllerPagerAdapter extends PagerAdapter {
-
-    private static final String KEY_SAVED_PAGES = "ControllerPagerAdapter.savedStates";
-    private static final String KEY_SAVES_STATE = "ControllerPagerAdapter.savesState";
-
-    private final Controller host;
-    private boolean savesState;
-    private SparseArray<Bundle> savedPages = new SparseArray<>();
-
-    /**
-     * Creates a new ControllerPagerAdapter using the passed host.
-     */
-    public ControllerPagerAdapter(Controller host, boolean saveControllerState) {
-        this.host = host;
-        savesState = saveControllerState;
-    }
-
-    /**
-     * Return the Controller associated with a specified position.
-     */
-    public abstract Controller getItem(int position);
-
-    @Override
-    public Object instantiateItem(ViewGroup container, int position) {
-        final String name = makeControllerName(container.getId(), getItemId(position));
-
-        Router router = host.getChildRouter(container, name);
-        if (savesState && !router.hasRootController()) {
-            Bundle routerSavedState = savedPages.get(position);
-
-            if (routerSavedState != null) {
-                router.restoreInstanceState(routerSavedState);
-            }
-        }
-
-        if (!router.hasRootController()) {
-            router.setRoot(RouterTransaction.with(getItem(position))
-                    .tag(name));
-        } else {
-            router.rebindIfNeeded();
-        }
-
-        return router.getControllerWithTag(name);
-    }
-
-    @Override
-    public void destroyItem(ViewGroup container, int position, Object object) {
-        Router router = ((Controller)object).getRouter();
-
-        if (savesState) {
-            Bundle savedState = new Bundle();
-            router.saveInstanceState(savedState);
-            savedPages.put(position, savedState);
-        }
-
-        host.removeChildRouter(router);
-    }
-
-    @Override
-    public boolean isViewFromObject(View view, Object object) {
-        return ((Controller)object).getView() == view;
-    }
-
-    @Override
-    public Parcelable saveState() {
-        Bundle bundle = new Bundle();
-        bundle.putBoolean(KEY_SAVES_STATE, savesState);
-        bundle.putSparseParcelableArray(KEY_SAVED_PAGES, savedPages);
-        return bundle;
-    }
-
-    @Override
-    public void restoreState(Parcelable state, ClassLoader loader) {
-        Bundle bundle = (Bundle)state;
-        if (state != null) {
-            savesState = bundle.getBoolean(KEY_SAVES_STATE, false);
-            savedPages = bundle.getSparseParcelableArray(KEY_SAVED_PAGES);
-        }
-    }
-
-    public long getItemId(int position) {
-        return position;
-    }
-
-    private static String makeControllerName(int viewId, long id) {
-        return viewId + ":" + id;
-    }
-
-}
@@ -1,27 +1,8 @@
-buildscript {
-    repositories {
-        jcenter()
-    }
-    dependencies {
-        classpath 'de.mobilej.unmock:UnMockPlugin:0.3.6'
-    }
-}
-
 apply plugin: 'com.android.library'
-apply plugin: 'de.mobilej.unmock'
+apply plugin: 'kotlin-android'

 android {
    compileSdkVersion rootProject.ext.compileSdkVersion
-    buildToolsVersion rootProject.ext.buildToolsVersion
-
-    lintOptions {
-        abortOnError false
-    }
-
-    compileOptions {
-        sourceCompatibility JavaVersion.VERSION_1_7
-        targetCompatibility JavaVersion.VERSION_1_7
-    }

    defaultConfig {
        minSdkVersion rootProject.ext.minSdkVersion
@@ -32,40 +13,17 @@ android {
    }
 }

-configurations {
-    lintChecks
-}
-
 dependencies {
-    testCompile rootProject.ext.junit
-    testCompile rootProject.ext.roboelectric
+    testImplementation rootProject.ext.junit
+    testImplementation rootProject.ext.roboelectric

-    compile rootProject.ext.supportAnnotations
+    api rootProject.ext.androidxAnnotations
+    api kotlinStd

-    lintChecks project(path: ':conductor-lint', configuration: 'lintChecks')
-}
-
-unMock {
-    downloadFrom 'https://oss.sonatype.org/content/groups/public/org/robolectric/android-all/4.3_r2-robolectric-0/android-all-4.3_r2-robolectric-0.jar'
-
-    keep "android.os.Bundle"
-    keep "android.os.BaseBundle"
-    keep "android.text.TextUtils"
-}
-
-task copyLintJar(type: Copy) {
-    from(configurations.lintChecks) {
-        rename { 'lint.jar' }
-    }
-    into 'build/intermediates/lint/'
-}
-
-project.afterEvaluate {
-    def compileLintTask = project.tasks.find { it.name == 'compileLint' }
-    compileLintTask.dependsOn(copyLintJar)
+    lintPublish project(':conductor-lint')
 }

 ext.artifactId = 'conductor'

 apply from: rootProject.file('dependencies.gradle')
-apply from: rootProject.file('gradle-mvn-push.gradle')
+apply plugin: "com.vanniktech.maven.publish"
@@ -2,4 +2,7 @@
 -keepclassmembers public class * extends com.bluelinelabs.conductor.Controller {
   public <init>();
   public <init>(android.os.Bundle);
-}
+}
+-keepclassmembers public class * extends com.bluelinelabs.conductor.ControllerChangeHandler {
+   public <init>();
+}
@@ -1,3 +1,3 @@
 <manifest package="com.bluelinelabs.conductor">
    <application />
-</manifest>
+</manifest>
@@ -2,18 +2,23 @@ package com.bluelinelabs.conductor;

 import android.app.Activity;
 import android.content.Intent;
+import android.content.IntentSender;
+import android.content.IntentSender.SendIntentException;
 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.view.ViewGroup;

 import com.bluelinelabs.conductor.ControllerChangeHandler.ControllerChangeListener;
 import com.bluelinelabs.conductor.internal.LifecycleHandler;
+import com.bluelinelabs.conductor.internal.TransactionIndexer;

 import java.util.List;

 public class ActivityHostedRouter extends Router {

    private LifecycleHandler lifecycleHandler;
+    private final TransactionIndexer transactionIndexer = new TransactionIndexer();

    public final void setHost(@NonNull LifecycleHandler lifecycleHandler, @NonNull ViewGroup container) {
        if (this.lifecycleHandler != lifecycleHandler || this.container != container) {
@@ -27,16 +32,32 @@ public class ActivityHostedRouter extends Router {

            this.lifecycleHandler = lifecycleHandler;
            this.container = container;
+
+            watchContainerAttach();
        }
    }

    @Override
+    public void saveInstanceState(@NonNull Bundle outState) {
+        super.saveInstanceState(outState);
+
+        transactionIndexer.saveInstanceState(outState);
+    }
+
+    @Override
+    public void restoreInstanceState(@NonNull Bundle savedInstanceState) {
+        super.restoreInstanceState(savedInstanceState);
+
+        transactionIndexer.restoreInstanceState(savedInstanceState);
+    }
+
+    @Override @Nullable
    public Activity getActivity() {
        return lifecycleHandler != null ? lifecycleHandler.getLifecycleActivity() : null;
    }

    @Override
-    public void onActivityDestroyed(Activity activity) {
+    public void onActivityDestroyed(@NonNull Activity activity) {
        super.onActivityDestroyed(activity);
        lifecycleHandler = null;
    }
@@ -49,37 +70,43 @@ public class ActivityHostedRouter extends Router {
    }

    @Override
-    public void onActivityResult(int requestCode, int resultCode, Intent data) {
+    public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        lifecycleHandler.onActivityResult(requestCode, resultCode, data);
    }

    @Override
-    void startActivity(Intent intent) {
+    void startActivity(@NonNull Intent intent) {
        lifecycleHandler.startActivity(intent);
    }

    @Override
-    void startActivityForResult(String instanceId, Intent intent, int requestCode) {
+    void startActivityForResult(@NonNull String instanceId, @NonNull Intent intent, int requestCode) {
        lifecycleHandler.startActivityForResult(instanceId, intent, requestCode);
    }

    @Override
-    void startActivityForResult(String instanceId, Intent intent, int requestCode, Bundle options) {
+    void startActivityForResult(@NonNull String instanceId, @NonNull Intent intent, int requestCode, @Nullable Bundle options) {
        lifecycleHandler.startActivityForResult(instanceId, intent, requestCode, options);
    }

    @Override
-    void registerForActivityResult(String instanceId, int requestCode) {
+    void startIntentSenderForResult(@NonNull String instanceId, @NonNull IntentSender intent, int requestCode, @Nullable Intent fillInIntent,
+                                    int flagsMask, int flagsValues, int extraFlags, @Nullable Bundle options) throws SendIntentException {
+        lifecycleHandler.startIntentSenderForResult(instanceId, intent, requestCode, fillInIntent, flagsMask, flagsValues, extraFlags, options);
+    }
+
+    @Override
+    void registerForActivityResult(@NonNull String instanceId, int requestCode) {
        lifecycleHandler.registerForActivityResult(instanceId, requestCode);
    }

    @Override
-    void unregisterForActivityResults(String instanceId) {
+    void unregisterForActivityResults(@NonNull String instanceId) {
        lifecycleHandler.unregisterForActivityResults(instanceId);
    }

    @Override
-    void requestPermissions(String instanceId, @NonNull String[] permissions, int requestCode) {
+    void requestPermissions(@NonNull String instanceId, @NonNull String[] permissions, int requestCode) {
        lifecycleHandler.requestPermissions(instanceId, permissions, requestCode);
    }

@@ -88,13 +115,24 @@ public class ActivityHostedRouter extends Router {
        return lifecycleHandler != null;
    }

-    @Override
+    @Override @NonNull
    List<Router> getSiblingRouters() {
        return lifecycleHandler.getRouters();
    }

-    @Override
+    @Override @NonNull
    Router getRootRouter() {
        return this;
    }
+
+    @Override @NonNull
+    TransactionIndexer getTransactionIndexer() {
+        return transactionIndexer;
+    }
+
+    @Override
+    public void onContextAvailable() {
+        super.onContextAvailable();
+    }
+
 }
@@ -2,6 +2,9 @@ package com.bluelinelabs.conductor;

 import android.os.Bundle;

+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Collections;
@@ -13,34 +16,37 @@ class Backstack implements Iterable<RouterTransaction> {

    private static final String KEY_ENTRIES = "Backstack.entries";

-    private final Deque<RouterTransaction> backStack = new ArrayDeque<>();
+    private final Deque<RouterTransaction> backstack = new ArrayDeque<>();

    @SuppressWarnings("BooleanMethodIsAlwaysInverted")
-    public boolean isEmpty() {
-        return backStack.isEmpty();
+    boolean isEmpty() {
+        return backstack.isEmpty();
    }

-    public int size() {
-        return backStack.size();
+    int size() {
+        return backstack.size();
    }

-    public RouterTransaction root() {
-        return backStack.size() > 0 ? backStack.getLast() : null;
+    @Nullable
+    RouterTransaction root() {
+        return backstack.size() > 0 ? backstack.getLast() : null;
    }

-    @Override
+    @Override @NonNull
    public Iterator<RouterTransaction> iterator() {
-        return backStack.iterator();
+        return backstack.iterator();
    }

-    public Iterator<RouterTransaction> reverseIterator() {
-        return backStack.descendingIterator();
+    @NonNull
+    Iterator<RouterTransaction> reverseIterator() {
+        return backstack.descendingIterator();
    }

-    public List<RouterTransaction> popTo(RouterTransaction transaction) {
+    @NonNull
+    List<RouterTransaction> popTo(@NonNull RouterTransaction transaction) {
        List<RouterTransaction> popped = new ArrayList<>();
-        if (backStack.contains(transaction)) {
-            while (backStack.peek() != transaction) {
+        if (backstack.contains(transaction)) {
+            while (backstack.peek() != transaction) {
                RouterTransaction poppedTransaction = pop();
                popped.add(poppedTransaction);
            }
@@ -50,25 +56,24 @@ class Backstack implements Iterable<RouterTransaction> {
        return popped;
    }

-    public RouterTransaction pop() {
-        RouterTransaction popped = backStack.pop();
-        popped.controller.destroy();
+    @NonNull
+    RouterTransaction pop() {
+        RouterTransaction popped = backstack.pop();
+        popped.controller().destroy();
        return popped;
    }

-    public RouterTransaction peek() {
-        return backStack.peek();
+    @Nullable
+    RouterTransaction peek() {
+        return backstack.peek();
    }

-    public void remove(RouterTransaction transaction) {
-        backStack.removeFirstOccurrence(transaction);
+    void push(@NonNull RouterTransaction transaction) {
+        backstack.push(transaction);
    }

-    public void push(RouterTransaction transaction) {
-        backStack.push(transaction);
-    }
-
-    public List<RouterTransaction> popAll() {
+    @NonNull
+    List<RouterTransaction> popAll() {
        List<RouterTransaction> list = new ArrayList<>();
        while (!isEmpty()) {
            list.add(pop());
@@ -76,42 +81,37 @@ class Backstack implements Iterable<RouterTransaction> {
        return list;
    }

-    public void setBackstack(List<RouterTransaction> backstack) {
-        for (RouterTransaction existingTransaction : backStack) {
-            boolean contains = false;
-            for (RouterTransaction newTransaction : backstack) {
-                if (existingTransaction.controller == newTransaction.controller) {
-                    contains = true;
-                    break;
-                }
-            }
-
-            if (!contains) {
-                existingTransaction.controller.destroy();
-            }
-        }
-
-        backStack.clear();
+    void setBackstack(@NonNull List<RouterTransaction> backstack) {
+        this.backstack.clear();
        for (RouterTransaction transaction : backstack) {
-            backStack.push(transaction);
+            this.backstack.push(transaction);
        }
    }

-    public void saveInstanceState(Bundle outState) {
-        ArrayList<Bundle> entryBundles = new ArrayList<>(backStack.size());
-        for (RouterTransaction entry : backStack) {
+    boolean contains(@NonNull Controller controller) {
+        for (RouterTransaction transaction : backstack) {
+            if (controller == transaction.controller()) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    void saveInstanceState(@NonNull Bundle outState) {
+        ArrayList<Bundle> entryBundles = new ArrayList<>(backstack.size());
+        for (RouterTransaction entry : backstack) {
            entryBundles.add(entry.saveInstanceState());
        }

        outState.putParcelableArrayList(KEY_ENTRIES, entryBundles);
    }

-    public void restoreInstanceState(Bundle savedInstanceState) {
+    void restoreInstanceState(@NonNull Bundle savedInstanceState) {
        ArrayList<Bundle> entryBundles = savedInstanceState.getParcelableArrayList(KEY_ENTRIES);
        if (entryBundles != null) {
            Collections.reverse(entryBundles);
            for (Bundle transactionBundle : entryBundles) {
-                backStack.push(new RouterTransaction(transactionBundle));
+                backstack.push(new RouterTransaction(transactionBundle));
            }
        }
    }
@@ -1,54 +0,0 @@
-package com.bluelinelabs.conductor;
-
-import android.annotation.TargetApi;
-import android.content.Context;
-import android.os.Build;
-import android.util.AttributeSet;
-import android.view.MotionEvent;
-import android.view.ViewGroup;
-import android.widget.FrameLayout;
-
-import com.bluelinelabs.conductor.ControllerChangeHandler.ControllerChangeListener;
-
-/**
- * A FrameLayout implementation that can be used to block user interactions while
- * {@link ControllerChangeHandler}s are performing changes. It is not required to use this
- * ViewGroup, but it can be helpful.
- */
-public class ChangeHandlerFrameLayout extends FrameLayout implements ControllerChangeListener {
-
-    private int inProgressTransactionCount;
-
-    public ChangeHandlerFrameLayout(Context context) {
-        super(context);
-    }
-
-    public ChangeHandlerFrameLayout(Context context, AttributeSet attrs) {
-        super(context, attrs);
-    }
-
-    public ChangeHandlerFrameLayout(Context context, AttributeSet attrs, int defStyleAttr) {
-        super(context, attrs, defStyleAttr);
-    }
-
-    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
-    public ChangeHandlerFrameLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
-        super(context, attrs, defStyleAttr, defStyleRes);
-    }
-
-    @Override
-    public boolean onInterceptTouchEvent(MotionEvent ev) {
-        return (inProgressTransactionCount > 0) || super.onInterceptTouchEvent(ev);
-    }
-
-    @Override
-    public void onChangeStarted(Controller to, Controller from, boolean isPush, ViewGroup container, ControllerChangeHandler handler) {
-        inProgressTransactionCount++;
-    }
-
-    @Override
-    public void onChangeCompleted(Controller to, Controller from, boolean isPush, ViewGroup container, ControllerChangeHandler handler) {
-        inProgressTransactionCount--;
-    }
-
-}
@@ -0,0 +1,60 @@
+package com.bluelinelabs.conductor
+
+import android.annotation.TargetApi
+import android.content.Context
+import android.os.Build
+import android.util.AttributeSet
+import android.view.MotionEvent
+import android.view.ViewGroup
+import android.widget.FrameLayout
+import com.bluelinelabs.conductor.ControllerChangeHandler.ControllerChangeListener
+
+/**
+ * A FrameLayout implementation that can be used to block user interactions while
+ * [ControllerChangeHandler]s are performing changes. It is not required to use this
+ * ViewGroup, but it can be helpful.
+ */
+open class ChangeHandlerFrameLayout : FrameLayout, ControllerChangeListener {
+
+  private var inProgressTransactionCount = 0
+
+  constructor(context: Context) : super(context)
+  constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
+  constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
+    context,
+    attrs,
+    defStyleAttr
+  )
+
+  @TargetApi(Build.VERSION_CODES.LOLLIPOP)
+  constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int, defStyleRes: Int) : super(
+    context,
+    attrs,
+    defStyleAttr,
+    defStyleRes
+  )
+
+  override fun onInterceptTouchEvent(ev: MotionEvent): Boolean {
+    return inProgressTransactionCount > 0 || super.onInterceptTouchEvent(ev)
+  }
+
+  override fun onChangeStarted(
+    to: Controller?,
+    from: Controller?,
+    isPush: Boolean,
+    container: ViewGroup,
+    handler: ControllerChangeHandler
+  ) {
+    inProgressTransactionCount++
+  }
+
+  override fun onChangeCompleted(
+    to: Controller?,
+    from: Controller?,
+    isPush: Boolean,
+    container: ViewGroup,
+    handler: ControllerChangeHandler
+  ) {
+    inProgressTransactionCount--
+  }
+}
@@ -1,38 +0,0 @@
-package com.bluelinelabs.conductor;
-
-import android.app.Activity;
-import android.os.Bundle;
-import android.support.annotation.NonNull;
-import android.view.ViewGroup;
-
-import com.bluelinelabs.conductor.internal.LifecycleHandler;
-
-/**
- * Point of initial interaction with Conductor. Used to attach a {@link Router} to your Activity.
- */
-public final class Conductor {
-    
-    private Conductor() {}
-    
-    /**
-     * Conductor will create a {@link Router} that has been initialized for your Activity and containing ViewGroup.
-     * If an existing {@link Router} is already associated with this Activity/ViewGroup pair, either in memory
-     * or in the savedInstanceState, that router will be used and rebound instead of creating a new one with
-     * an empty backstack.
-     *
-     * @param activity The Activity that will host the {@link Router} being attached.
-     * @param container The ViewGroup in which the {@link Router}'s {@link Controller} views will be hosted
-     * @param savedInstanceState The savedInstanceState passed into the hosting Activity's onCreate method. Used
-     *                           for restoring the Router's state if possible.
-     * @return A fully configured {@link Router} instance for use with this Activity/ViewGroup pair.
-     */
-    public static Router attachRouter(@NonNull Activity activity, @NonNull ViewGroup container, Bundle savedInstanceState) {
-        LifecycleHandler lifecycleHandler = LifecycleHandler.install(activity);
-
-        Router router = lifecycleHandler.getRouter(container, savedInstanceState);
-        router.rebindIfNeeded();
-
-        return router;
-    }
-
-}
@@ -0,0 +1,32 @@
+package com.bluelinelabs.conductor
+
+import android.app.Activity
+import android.os.Bundle
+import android.view.ViewGroup
+import androidx.annotation.UiThread
+import com.bluelinelabs.conductor.internal.LifecycleHandler
+import com.bluelinelabs.conductor.internal.ensureMainThread
+
+/**
+ * Conductor will create a [Router] that has been initialized for your Activity and containing ViewGroup.
+ * If an existing [Router] is already associated with this Activity/ViewGroup pair, either in memory
+ * or in the savedInstanceState, that router will be used and rebound instead of creating a new one with
+ * an empty backstack.
+ *
+ * @param activity The Activity that will host the [Router] being attached.
+ * @param container The ViewGroup in which the [Router]'s [Controller] views will be hosted
+ * @param savedInstanceState The savedInstanceState passed into the hosting Activity's onCreate method. Used
+ * for restoring the Router's state if possible.
+ * @return A fully configured [Router] instance for use with this Activity/ViewGroup pair.
+ */
+@UiThread
+object Conductor {
+  
+  @JvmStatic
+  fun attachRouter(activity: Activity, container: ViewGroup, savedInstanceState: Bundle?): Router {
+    ensureMainThread()
+    return LifecycleHandler.install(activity)
+      .getRouter(container, savedInstanceState)
+      .also { it.rebindIfNeeded() }
+  }
+}
@@ -1,15 +1,16 @@
 package com.bluelinelabs.conductor;

 import android.os.Bundle;
-import android.support.annotation.NonNull;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.ViewParent;

+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import com.bluelinelabs.conductor.changehandler.SimpleSwapChangeHandler;
 import com.bluelinelabs.conductor.internal.ClassUtils;

-import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -24,20 +25,21 @@ public abstract class ControllerChangeHandler {
    private static final String KEY_CLASS_NAME = "ControllerChangeHandler.className";
    private static final String KEY_SAVED_STATE = "ControllerChangeHandler.savedState";

-    private static final Map<String, ControllerChangeHandler> inProgressPushHandlers = new HashMap<>();
+    static final Map<String, ChangeHandlerData> inProgressChangeHandlers = new HashMap<>();

-    private boolean forceRemoveViewOnPush;
+    boolean forceRemoveViewOnPush;
+    private boolean hasBeenUsed;

    /**
     * Responsible for swapping Views from one Controller to another.
     *
     * @param container      The container these Views are hosted in.
-     * @param from           The previous View in the container, if any.
-     * @param to             The next View that should be put in the container, if any.
+     * @param from           The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to             The next View that should be put in the container or {@code null} if no Controller is being transitioned to
     * @param isPush         True if this is a push transaction, false if it's a pop.
     * @param changeListener This listener must be called when any transitions or animations are completed.
     */
-    public abstract void performChange(@NonNull ViewGroup container, View from, View to, boolean isPush, @NonNull ControllerChangeCompletedListener changeListener);
+    public abstract void performChange(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, @NonNull ControllerChangeCompletedListener changeListener);

    public ControllerChangeHandler() {
        ensureDefaultConstructor();
@@ -48,30 +50,56 @@ public abstract class ControllerChangeHandler {
     *
     * @param bundle The Bundle into which data should be stored.
     */
-    public void saveToBundle(@NonNull Bundle bundle) { }
+    public void saveToBundle(@NonNull Bundle bundle) {
+    }

    /**
     * Restores data that was saved in the {@link #saveToBundle(Bundle bundle)} method.
     *
     * @param bundle The bundle that has data to be restored
     */
-    public void restoreFromBundle(@NonNull Bundle bundle) { }
+    public void restoreFromBundle(@NonNull Bundle bundle) {
+    }

    /**
     * Will be called on change handlers that push a controller if the controller being pushed is
     * popped before it has completed.
     *
-     * @param newHandler the change handler that has caused this push to be aborted
-     * @param newTop     the controller that will now be at the top of the backstack
+     * @param newHandler The change handler that has caused this push to be aborted
+     * @param newTop     The Controller that will now be at the top of the backstack or {@code null}
+     *                   if there will be no new Controller at the top
     */
-    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, Controller newTop) { }
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
+    }

    /**
     * Will be called on change handlers that push a controller if the controller being pushed is
     * needs to be attached immediately, without any animations or transitions.
     */
-    public void completeImmediately() { }
+    public void completeImmediately() {
+    }

+    /**
+     * Returns a copy of this ControllerChangeHandler. This method is internally used by the library, so
+     * ensure it will return an exact copy of your handler if overriding. If not overriding, the handler
+     * will be saved and restored from the Bundle format.
+     */
+    @NonNull
+    public ControllerChangeHandler copy() {
+        return fromBundle(toBundle());
+    }
+
+    /**
+     * Returns whether or not this is a reusable ControllerChangeHandler. Defaults to false and should
+     * ONLY be overridden if there are absolutely no side effects to using this handler more than once.
+     * In the case that a handler is not reusable, it will be copied using the {@link #copy()} method
+     * prior to use.
+     */
+    public boolean isReusable() {
+        return false;
+    }
+
+    @NonNull
    final Bundle toBundle() {
        Bundle bundle = new Bundle();
        bundle.putString(KEY_CLASS_NAME, getClass().getName());
@@ -83,10 +111,6 @@ public abstract class ControllerChangeHandler {
        return bundle;
    }

-    final ControllerChangeHandler copy() {
-        return fromBundle(toBundle());
-    }
-
    private void ensureDefaultConstructor() {
        try {
            getClass().getConstructor();
@@ -95,7 +119,8 @@ public abstract class ControllerChangeHandler {
        }
    }

-    public static ControllerChangeHandler fromBundle(Bundle bundle) {
+    @Nullable
+    public static ControllerChangeHandler fromBundle(@Nullable Bundle bundle) {
        if (bundle != null) {
            String className = bundle.getString(KEY_CLASS_NAME);
            ControllerChangeHandler changeHandler = ClassUtils.newInstance(className);
@@ -107,40 +132,59 @@ public abstract class ControllerChangeHandler {
        }
    }

-    static boolean completePushImmediately(String controllerInstanceId) {
-        ControllerChangeHandler changeHandler = inProgressPushHandlers.get(controllerInstanceId);
-        if (changeHandler != null) {
-            changeHandler.completeImmediately();
-            inProgressPushHandlers.remove(controllerInstanceId);
+    static boolean completeHandlerImmediately(@NonNull String controllerInstanceId) {
+        ChangeHandlerData changeHandlerData = inProgressChangeHandlers.get(controllerInstanceId);
+        if (changeHandlerData != null) {
+            changeHandlerData.changeHandler.completeImmediately();
+            inProgressChangeHandlers.remove(controllerInstanceId);
            return true;
        }
        return false;
    }

-    public static void abortPush(Controller toAbort, Controller newController, ControllerChangeHandler newChangeHandler) {
-        ControllerChangeHandler handlerForPush = inProgressPushHandlers.get(toAbort.getInstanceId());
-        if (handlerForPush != null) {
-            handlerForPush.onAbortPush(newChangeHandler, newController);
-            inProgressPushHandlers.remove(toAbort.getInstanceId());
+    static void abortOrComplete(@NonNull Controller toAbort, @Nullable Controller newController, @NonNull ControllerChangeHandler newChangeHandler) {
+        ChangeHandlerData changeHandlerData = inProgressChangeHandlers.get(toAbort.getInstanceId());
+        if (changeHandlerData != null) {
+            if (changeHandlerData.isPush) {
+                changeHandlerData.changeHandler.onAbortPush(newChangeHandler, newController);
+            } else {
+                changeHandlerData.changeHandler.completeImmediately();
+            }
+
+            inProgressChangeHandlers.remove(toAbort.getInstanceId());
        }
    }

-    public static void executeChange(final Controller to, final Controller from, boolean isPush, ViewGroup container, ControllerChangeHandler inHandler) {
-        executeChange(to, from, isPush, container, inHandler, new ArrayList<ControllerChangeListener>());
+    static void executeChange(@NonNull final ChangeTransaction transaction) {
+        executeChange(transaction.to, transaction.from, transaction.isPush, transaction.container, transaction.changeHandler, transaction.listeners);
    }

-    public static void executeChange(final Controller to, final Controller from, final boolean isPush, final ViewGroup container, final ControllerChangeHandler inHandler, @NonNull final List<ControllerChangeListener> listeners) {
+    private static void executeChange(@Nullable final Controller to, @Nullable final Controller from, final boolean isPush, @Nullable final ViewGroup container, @Nullable final ControllerChangeHandler inHandler, @NonNull final List<ControllerChangeListener> listeners) {
        if (container != null) {
-            final ControllerChangeHandler handler = inHandler != null ? inHandler : new SimpleSwapChangeHandler();
+            final ControllerChangeHandler handler;
+            if (inHandler == null) {
+                handler = new SimpleSwapChangeHandler();
+            } else if (inHandler.hasBeenUsed && !inHandler.isReusable()) {
+                handler = inHandler.copy();
+            } else {
+                handler = inHandler;
+            }
+            handler.hasBeenUsed = true;

-            if (isPush && to != null) {
-                inProgressPushHandlers.put(to.getInstanceId(), handler);
-            } else if (!isPush && from != null) {
-                abortPush(from, to, handler);
+            if (from != null) {
+                if (isPush) {
+                    completeHandlerImmediately(from.getInstanceId());
+                } else {
+                    abortOrComplete(from, to, handler);
+                }
+            }
+
+            if (to != null) {
+                inProgressChangeHandlers.put(to.getInstanceId(), new ChangeHandlerData(handler, isPush));
            }

            for (ControllerChangeListener listener : listeners) {
-                listener.onChangeStarted(to, from, isPush, container, inHandler);
+                listener.onChangeStarted(to, from, isPush, container, handler);
            }

            final ControllerChangeType toChangeType = isPush ? ControllerChangeType.PUSH_ENTER : ControllerChangeType.POP_ENTER;
@@ -162,33 +206,37 @@ public abstract class ControllerChangeHandler {
                fromView = null;
            }

-            handler.performChange(container, fromView, toView, isPush, new ControllerChangeCompletedListener() {
-                @Override
-                public void onChangeCompleted() {
-                    if (from != null) {
-                        from.changeEnded(handler, fromChangeType);
-                    }
+            handler.performChange(container, fromView, toView, isPush, () -> {
+                if (from != null) {
+                    from.changeEnded(handler, fromChangeType);
+                }

-                    if (to != null) {
-                        inProgressPushHandlers.remove(to.getInstanceId());
-                        to.changeEnded(handler, toChangeType);
-                    }
+                if (to != null) {
+                    inProgressChangeHandlers.remove(to.getInstanceId());
+                    to.changeEnded(handler, toChangeType);
+                }

-                    for (ControllerChangeListener listener : listeners) {
-                        listener.onChangeCompleted(to, from, isPush, container, inHandler);
-                    }
+                for (ControllerChangeListener listener : listeners) {
+                    listener.onChangeCompleted(to, from, isPush, container, handler);
+                }

-                    if (handler.forceRemoveViewOnPush && fromView != null) {
-                        ViewParent fromParent = fromView.getParent();
-                        if (fromParent != null && fromParent instanceof ViewGroup) {
-                            ((ViewGroup)fromParent).removeView(fromView);
-                        }
+                if (handler.forceRemoveViewOnPush && fromView != null) {
+                    ViewParent fromParent = fromView.getParent();
+                    if (fromParent != null && fromParent instanceof ViewGroup) {
+                        ((ViewGroup) fromParent).removeView(fromView);
                    }
                }
+
+                if (handler.removesFromViewOnPush() && from != null) {
+                    from.setNeedsAttach(false);
+                }
            });
        }
    }

+    protected void onEnd() {
+    }
+
    public boolean removesFromViewOnPush() {
        return true;
    }
@@ -204,24 +252,49 @@ public abstract class ControllerChangeHandler {
        /**
         * Called when a {@link ControllerChangeHandler} has started changing {@link Controller}s
         *
-         * @param to        The new Controller
-         * @param from      The old Controller
+         * @param to        The new Controller or {@code null} if no Controller is being transitioned to
+         * @param from      The old Controller or {@code null} if there was no Controller before this transition
         * @param isPush    True if this is a push operation, or false if it's a pop.
         * @param container The containing ViewGroup
         * @param handler   The change handler being used.
         */
-        void onChangeStarted(Controller to, Controller from, boolean isPush, ViewGroup container, ControllerChangeHandler handler);
+        default void onChangeStarted(@Nullable Controller to, @Nullable Controller from, boolean isPush, @NonNull ViewGroup container, @NonNull ControllerChangeHandler handler) {
+        }

        /**
         * Called when a {@link ControllerChangeHandler} has completed changing {@link Controller}s
         *
-         * @param to        The new Controller
-         * @param from      The old Controller
-         * @param isPush    True if this was a push operation, or false if it's a pop.
+         * @param to        The new Controller or {@code null} if no Controller is being transitioned to
+         * @param from      The old Controller or {@code null} if there was no Controller before this transition
+         * @param isPush    True if this was a push operation, or false if it's a pop
         * @param container The containing ViewGroup
         * @param handler   The change handler that was used.
         */
-        void onChangeCompleted(Controller to, Controller from, boolean isPush, ViewGroup container, ControllerChangeHandler handler);
+        default void onChangeCompleted(@Nullable Controller to, @Nullable Controller from, boolean isPush, @NonNull ViewGroup container, @NonNull ControllerChangeHandler handler) {
+        }
+    }
+
+    static class ChangeTransaction {
+        @Nullable
+        final Controller to;
+        @Nullable
+        final Controller from;
+        final boolean isPush;
+        @Nullable
+        final ViewGroup container;
+        @Nullable
+        final ControllerChangeHandler changeHandler;
+        @NonNull
+        final List<ControllerChangeListener> listeners;
+
+        public ChangeTransaction(@Nullable Controller to, @Nullable Controller from, boolean isPush, @Nullable ViewGroup container, @Nullable ControllerChangeHandler changeHandler, @NonNull List<ControllerChangeListener> listeners) {
+            this.to = to;
+            this.from = from;
+            this.isPush = isPush;
+            this.container = container;
+            this.changeHandler = changeHandler;
+            this.listeners = listeners;
+        }
    }

    /**
@@ -235,4 +308,14 @@ public abstract class ControllerChangeHandler {
        void onChangeCompleted();
    }

+    private static class ChangeHandlerData {
+        public final ControllerChangeHandler changeHandler;
+        public final boolean isPush;
+
+        public ChangeHandlerData(ControllerChangeHandler changeHandler, boolean isPush) {
+            this.changeHandler = changeHandler;
+            this.isPush = isPush;
+        }
+    }
+
 }
@@ -1,26 +0,0 @@
-package com.bluelinelabs.conductor;
-
-/**
- * All possible types of {@link Controller} changes to be used in {@link ControllerChangeHandler}s
- */
-public enum ControllerChangeType {
-    /** The Controller is being pushed to the host container */
-    PUSH_ENTER(true, true),
-
-    /** The Controller is being pushed to the backstack as another Controller is pushed to the host container */
-    PUSH_EXIT(true, false),
-
-    /** The Controller is being popped from the backstack and placed in the host container as another Controller is popped */
-    POP_ENTER(false, true),
-
-    /** The Controller is being popped from the host container */
-    POP_EXIT(false, false);
-
-    public boolean isPush;
-    public boolean isEnter;
-
-    ControllerChangeType(boolean isPush, boolean isEnter) {
-        this.isPush = isPush;
-        this.isEnter = isEnter;
-    }
-}
@@ -0,0 +1,18 @@
+package com.bluelinelabs.conductor
+
+/**
+ * All possible types of [Controller] changes to be used in [ControllerChangeHandler]s
+ */
+enum class ControllerChangeType(@JvmField val isPush: Boolean, @JvmField val isEnter: Boolean) {
+  /** The Controller is being pushed to the host container  */
+  PUSH_ENTER(true, true),
+
+  /** The Controller is being pushed to the backstack as another Controller is pushed to the host container  */
+  PUSH_EXIT(true, false),
+
+  /** The Controller is being popped from the backstack and placed in the host container as another Controller is popped  */
+  POP_ENTER(false, true),
+
+  /** The Controller is being popped from the host container  */
+  POP_EXIT(false, false);
+}
@@ -2,15 +2,21 @@ package com.bluelinelabs.conductor;

 import android.app.Activity;
 import android.content.Intent;
+import android.content.IntentSender;
+import android.content.IntentSender.SendIntentException;
 import android.os.Bundle;
-import android.support.annotation.IdRes;
-import android.support.annotation.NonNull;
 import android.view.ViewGroup;

+import androidx.annotation.IdRes;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import com.bluelinelabs.conductor.ControllerChangeHandler.ControllerChangeListener;
+import com.bluelinelabs.conductor.internal.TransactionIndexer;

 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;

 class ControllerHostedRouter extends Router {

@@ -21,10 +27,11 @@ class ControllerHostedRouter extends Router {

    @IdRes private int hostId;
    private String tag;
+    private boolean isDetachFrozen;

    ControllerHostedRouter() { }

-    ControllerHostedRouter(int hostId, String tag) {
+    ControllerHostedRouter(int hostId, @Nullable String tag) {
        this.hostId = hostId;
        this.tag = tag;
    }
@@ -39,6 +46,12 @@ class ControllerHostedRouter extends Router {

            hostController = controller;
            this.container = container;
+
+            for (RouterTransaction transaction : backstack) {
+                transaction.controller().setParentController(controller);
+            }
+
+            watchContainerAttach();
        }
    }

@@ -50,12 +63,12 @@ class ControllerHostedRouter extends Router {
        final List<Controller> controllersToDestroy = new ArrayList<>(destroyingControllers);
        for (Controller controller : controllersToDestroy) {
            if (controller.getView() != null) {
-                controller.detach(controller.getView(), true);
+                controller.detach(controller.getView(), true, false);
            }
        }
        for (RouterTransaction transaction : backstack) {
-            if (transaction.controller.getView() != null) {
-                transaction.controller.detach(transaction.controller.getView(), true);
+            if (transaction.controller().getView() != null) {
+                transaction.controller().detach(transaction.controller().getView(), true, false);
            }
        }

@@ -65,31 +78,50 @@ class ControllerHostedRouter extends Router {
    }

    final void setDetachFrozen(boolean frozen) {
+        isDetachFrozen = frozen;
        for (RouterTransaction transaction : backstack) {
-            transaction.controller.setDetachFrozen(frozen);
+            transaction.controller().setDetachFrozen(frozen);
        }
    }

    @Override
-    void destroy() {
+    void destroy(boolean popViews) {
        setDetachFrozen(false);
-        super.destroy();
+        super.destroy(popViews);
    }

    @Override
+    protected void pushToBackstack(@NonNull RouterTransaction entry) {
+        if (isDetachFrozen) {
+            entry.controller().setDetachFrozen(true);
+        }
+        super.pushToBackstack(entry);
+    }
+
+    @Override
+    public void setBackstack(@NonNull List<RouterTransaction> newBackstack, @Nullable ControllerChangeHandler changeHandler) {
+        if (isDetachFrozen) {
+            for (RouterTransaction transaction : newBackstack) {
+                transaction.controller().setDetachFrozen(true);
+            }
+        }
+        super.setBackstack(newBackstack, changeHandler);
+    }
+
+    @Override @Nullable
    public Activity getActivity() {
        return hostController != null ? hostController.getActivity() : null;
    }

    @Override
-    public void onActivityDestroyed(Activity activity) {
+    public void onActivityDestroyed(@NonNull Activity activity) {
        super.onActivityDestroyed(activity);

        removeHost();
    }

    @Override
-    public void onActivityResult(int requestCode, int resultCode, Intent data) {
+    public void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().onActivityResult(requestCode, resultCode, data);
        }
@@ -103,42 +135,49 @@ class ControllerHostedRouter extends Router {
    }

    @Override
-    void startActivity(Intent intent) {
+    void startActivity(@NonNull Intent intent) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().startActivity(intent);
        }
    }

    @Override
-    void startActivityForResult(String instanceId, Intent intent, int requestCode) {
+    void startActivityForResult(@NonNull String instanceId, @NonNull Intent intent, int requestCode) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().startActivityForResult(instanceId, intent, requestCode);
        }
    }

    @Override
-    void startActivityForResult(String instanceId, Intent intent, int requestCode, Bundle options) {
+    void startActivityForResult(@NonNull String instanceId, @NonNull Intent intent, int requestCode, @Nullable Bundle options) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().startActivityForResult(instanceId, intent, requestCode, options);
        }
    }

    @Override
-    void registerForActivityResult(String instanceId, int requestCode) {
+    void startIntentSenderForResult(@NonNull String instanceId, @NonNull IntentSender intent, int requestCode, @Nullable Intent fillInIntent, int flagsMask, int flagsValues, int extraFlags, @Nullable Bundle options) throws SendIntentException {
+        if (hostController != null && hostController.getRouter() != null) {
+            hostController.getRouter().startIntentSenderForResult(instanceId, intent, requestCode, fillInIntent, flagsMask, flagsValues, extraFlags, options);
+        }
+    }
+
+    @Override
+    void registerForActivityResult(@NonNull String instanceId, int requestCode) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().registerForActivityResult(instanceId, requestCode);
        }
    }

    @Override
-    void unregisterForActivityResults(String instanceId) {
+    void unregisterForActivityResults(@NonNull String instanceId) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().unregisterForActivityResults(instanceId);
        }
    }

    @Override
-    void requestPermissions(String instanceId, String[] permissions, int requestCode) {
+    void requestPermissions(@NonNull String instanceId, @NonNull String[] permissions, int requestCode) {
        if (hostController != null && hostController.getRouter() != null) {
            hostController.getRouter().requestPermissions(instanceId, permissions, requestCode);
        }
@@ -150,7 +189,7 @@ class ControllerHostedRouter extends Router {
    }

    @Override
-    public void saveInstanceState(Bundle outState) {
+    public void saveInstanceState(@NonNull Bundle outState) {
        super.saveInstanceState(outState);

        outState.putInt(KEY_HOST_ID, hostId);
@@ -158,7 +197,7 @@ class ControllerHostedRouter extends Router {
    }

    @Override
-    public void restoreInstanceState(Bundle savedInstanceState) {
+    public void restoreInstanceState(@NonNull Bundle savedInstanceState) {
        super.restoreInstanceState(savedInstanceState);

        hostId = savedInstanceState.getInt(KEY_HOST_ID);
@@ -166,20 +205,21 @@ class ControllerHostedRouter extends Router {
    }

    @Override
-    void setControllerRouter(Controller controller) {
-        super.setControllerRouter(controller);
+    void setControllerRouter(@NonNull Controller controller) {
        controller.setParentController(hostController);
+        super.setControllerRouter(controller);
    }

    int getHostId() {
        return hostId;
    }

+    @Nullable
    String getTag() {
        return tag;
    }

-    @Override
+    @Override @NonNull
    List<Router> getSiblingRouters() {
        List<Router> list = new ArrayList<>();
        list.addAll(hostController.getChildRouters());
@@ -187,7 +227,7 @@ class ControllerHostedRouter extends Router {
        return list;
    }

-    @Override
+    @Override @NonNull
    Router getRootRouter() {
        if (hostController != null && hostController.getRouter() != null) {
            return hostController.getRouter().getRootRouter();
@@ -195,4 +235,22 @@ class ControllerHostedRouter extends Router {
            return this;
        }
    }
+
+    @Override @NonNull
+    TransactionIndexer getTransactionIndexer() {
+        Router rootRouter = getRootRouter();
+        if (rootRouter == this) {
+            String debugInfo;
+            if (hostController != null) {
+                debugInfo = String.format(Locale.ENGLISH, "%s (attached? %b, destroyed? %b, parent: %s)",
+                        hostController.getClass().getSimpleName(), hostController.isAttached(), hostController.isBeingDestroyed, hostController.getParentController());
+            } else {
+                debugInfo = "null host controller";
+            }
+            throw new IllegalStateException("Unable to retrieve TransactionIndexer from " + debugInfo);
+        } else {
+            return getRootRouter().getTransactionIndexer();
+        }
+    }
+
 }
@@ -1,38 +0,0 @@
-package com.bluelinelabs.conductor;
-
-import android.os.Bundle;
-import android.support.annotation.NonNull;
-import android.support.annotation.Nullable;
-import android.view.LayoutInflater;
-import android.view.View;
-import android.view.ViewGroup;
-
-/**
- * A simple controller subclass that changes the onCreateView signature to include a saved view state parameter.
- * This is necessary for some third party libraries like Google Maps, which require passing in a saved state
- * bundle at the time of creation.
- */
-abstract public class RestoreViewOnCreateController extends Controller {
-
-    @NonNull
-    @Override
-    protected final View onCreateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container) {
-        return onCreateView(inflater, container, viewState);
-    }
-
-    /**
-     * Called when the controller is ready to display its view. A valid view must be returned. The standard body
-     * for this method will be {@code return inflater.inflate(R.layout.my_layout, container, false);}, plus
-     * any binding and state restoration code.
-     *
-     * @param inflater       The LayoutInflater that should be used to inflate views
-     * @param container      The parent view that this Controller's view will eventually be attached to.
-     *                       This Controller's view should NOT be added in this method. It is simply passed in
-     *                       so that valid LayoutParams can be used during inflation.
-     * @param savedViewState A bundle for the view's state, which would have been created in {@link #onSaveViewState(View, Bundle)},
-     *                       or null if no saved state exists.
-     */
-    @NonNull
-    protected abstract View onCreateView(@NonNull LayoutInflater inflater, @NonNull ViewGroup container, @Nullable Bundle savedViewState);
-
-}
@@ -1,116 +0,0 @@
-package com.bluelinelabs.conductor;
-
-import android.os.Bundle;
-import android.support.annotation.NonNull;
-
-/**
- * Metadata used for adding {@link Controller}s to a {@link Router}.
- */
-public class RouterTransaction {
-
-    private static final String KEY_VIEW_CONTROLLER_BUNDLE = "RouterTransaction.controller.bundle";
-    private static final String KEY_PUSH_TRANSITION = "RouterTransaction.pushControllerChangeHandler";
-    private static final String KEY_POP_TRANSITION = "RouterTransaction.popControllerChangeHandler";
-    private static final String KEY_TAG = "RouterTransaction.tag";
-    private static final String KEY_ATTACHED_TO_ROUTER = "RouterTransaction.attachedToRouter";
-
-    @NonNull final Controller controller;
-    private String tag;
-
-    private ControllerChangeHandler pushControllerChangeHandler;
-    private ControllerChangeHandler popControllerChangeHandler;
-    private boolean attachedToRouter;
-
-    public static RouterTransaction with(@NonNull Controller controller) {
-        return new RouterTransaction(controller);
-    }
-
-    private RouterTransaction(@NonNull Controller controller) {
-        this.controller = controller;
-    }
-
-    RouterTransaction(@NonNull Bundle bundle) {
-        controller = Controller.newInstance(bundle.getBundle(KEY_VIEW_CONTROLLER_BUNDLE));
-        pushControllerChangeHandler = ControllerChangeHandler.fromBundle(bundle.getBundle(KEY_PUSH_TRANSITION));
-        popControllerChangeHandler = ControllerChangeHandler.fromBundle(bundle.getBundle(KEY_POP_TRANSITION));
-        tag = bundle.getString(KEY_TAG);
-        attachedToRouter = bundle.getBoolean(KEY_ATTACHED_TO_ROUTER);
-    }
-
-    void onAttachedToRouter() {
-        attachedToRouter = true;
-    }
-
-    public Controller controller() {
-        return controller;
-    }
-
-    public String tag() {
-        return tag;
-    }
-
-    public RouterTransaction tag(String tag) {
-        if (!attachedToRouter) {
-            this.tag = tag;
-            return this;
-        } else {
-            throw new RuntimeException(getClass().getSimpleName() + "s can not be modified after being added to a Router.");
-        }
-    }
-
-    public ControllerChangeHandler pushChangeHandler() {
-        ControllerChangeHandler handler = controller.getOverriddenPushHandler();
-        if (handler == null) {
-            handler = pushControllerChangeHandler;
-        }
-        return handler;
-    }
-
-    public RouterTransaction pushChangeHandler(ControllerChangeHandler handler) {
-        if (!attachedToRouter) {
-            pushControllerChangeHandler = handler;
-            return this;
-        } else {
-            throw new RuntimeException(getClass().getSimpleName() + "s can not be modified after being added to a Router.");
-        }
-    }
-
-    public ControllerChangeHandler popChangeHandler() {
-        ControllerChangeHandler handler = controller.getOverriddenPopHandler();
-        if (handler == null) {
-            handler = popControllerChangeHandler;
-        }
-        return handler;
-    }
-
-    public RouterTransaction popChangeHandler(ControllerChangeHandler handler) {
-        if (!attachedToRouter) {
-            popControllerChangeHandler = handler;
-            return this;
-        } else {
-            throw new RuntimeException(getClass().getSimpleName() + "s can not be modified after being added to a Router.");
-        }
-    }
-
-    /**
-     * Used to serialize this transaction into a Bundle
-     */
-    public Bundle saveInstanceState() {
-        Bundle bundle = new Bundle();
-
-        bundle.putBundle(KEY_VIEW_CONTROLLER_BUNDLE, controller.saveInstanceState());
-
-        if (pushControllerChangeHandler != null) {
-            bundle.putBundle(KEY_PUSH_TRANSITION, pushControllerChangeHandler.toBundle());
-        }
-        if (popControllerChangeHandler != null) {
-            bundle.putBundle(KEY_POP_TRANSITION, popControllerChangeHandler.toBundle());
-        }
-
-        bundle.putString(KEY_TAG, tag);
-        bundle.putBoolean(KEY_ATTACHED_TO_ROUTER, attachedToRouter);
-
-        return bundle;
-    }
-
-}
@@ -0,0 +1,123 @@
+package com.bluelinelabs.conductor
+
+import android.os.Bundle
+import androidx.annotation.RestrictTo
+import androidx.annotation.RestrictTo.Scope.LIBRARY
+import com.bluelinelabs.conductor.internal.TransactionIndexer
+
+private const val INVALID_INDEX = -1
+private const val KEY_VIEW_CONTROLLER_BUNDLE = "RouterTransaction.controller.bundle"
+private const val KEY_PUSH_TRANSITION = "RouterTransaction.pushControllerChangeHandler"
+private const val KEY_POP_TRANSITION = "RouterTransaction.popControllerChangeHandler"
+private const val KEY_TAG = "RouterTransaction.tag"
+private const val KEY_INDEX = "RouterTransaction.transactionIndex"
+private const val KEY_ATTACHED_TO_ROUTER = "RouterTransaction.attachedToRouter"
+
+/**
+ * Metadata used for adding [Controller]s to a [Router].
+ */
+class RouterTransaction
+private constructor(
+  @get:JvmName("controller")
+  val controller: Controller,
+  private var tag: String? = null,
+  private var pushControllerChangeHandler: ControllerChangeHandler? = null,
+  private var popControllerChangeHandler: ControllerChangeHandler? = null,
+  private var attachedToRouter: Boolean = false,
+  @RestrictTo(LIBRARY)
+  var transactionIndex: Int = INVALID_INDEX
+) {
+
+
+  @RestrictTo(LIBRARY)
+  internal constructor(bundle: Bundle) : this(
+    controller = Controller.newInstance(bundle.getBundle(KEY_VIEW_CONTROLLER_BUNDLE)!!),
+    pushControllerChangeHandler = ControllerChangeHandler.fromBundle(
+      bundle.getBundle(
+        KEY_PUSH_TRANSITION
+      )
+    ),
+    popControllerChangeHandler = ControllerChangeHandler.fromBundle(
+      bundle.getBundle(
+        KEY_POP_TRANSITION
+      )
+    ),
+    tag = bundle.getString(KEY_TAG),
+    transactionIndex = bundle.getInt(KEY_INDEX),
+    attachedToRouter = bundle.getBoolean(KEY_ATTACHED_TO_ROUTER)
+  )
+
+  fun onAttachedToRouter() {
+    attachedToRouter = true
+  }
+
+  fun tag(): String? = tag
+
+  fun tag(tag: String?): RouterTransaction {
+    return if (!attachedToRouter) {
+      this.tag = tag
+      this
+    } else {
+      throw RuntimeException(javaClass.simpleName + "s can not be modified after being added to a Router.")
+    }
+  }
+
+  fun pushChangeHandler(): ControllerChangeHandler? {
+    return controller.overriddenPushHandler ?: pushControllerChangeHandler
+  }
+
+  fun pushChangeHandler(handler: ControllerChangeHandler?): RouterTransaction {
+    return if (!attachedToRouter) {
+      pushControllerChangeHandler = handler
+      this
+    } else {
+      throw RuntimeException("${javaClass.simpleName}s can not be modified after being added to a Router.")
+    }
+  }
+
+  fun popChangeHandler(): ControllerChangeHandler? {
+    return controller.overriddenPopHandler ?: popControllerChangeHandler
+  }
+
+  fun popChangeHandler(handler: ControllerChangeHandler?): RouterTransaction {
+    return if (!attachedToRouter) {
+      popControllerChangeHandler = handler
+      this
+    } else {
+      throw RuntimeException("${javaClass.simpleName}s can not be modified after being added to a Router.")
+    }
+  }
+
+  fun ensureValidIndex(indexer: TransactionIndexer) {
+    if (transactionIndex == INVALID_INDEX) {
+      transactionIndex = indexer.nextIndex()
+    }
+  }
+
+  /**
+   * Used to serialize this transaction into a Bundle
+   */
+  fun saveInstanceState(): Bundle = Bundle().apply {
+    putBundle(KEY_VIEW_CONTROLLER_BUNDLE, controller.saveInstanceState())
+    pushControllerChangeHandler?.let { putBundle(KEY_PUSH_TRANSITION, it.toBundle()) }
+    popControllerChangeHandler?.let { putBundle(KEY_POP_TRANSITION, it.toBundle()) }
+    putString(KEY_TAG, tag)
+    putInt(KEY_INDEX, transactionIndex)
+    putBoolean(KEY_ATTACHED_TO_ROUTER, attachedToRouter)
+  }
+
+  companion object {
+
+    @JvmStatic
+    fun with(controller: Controller): RouterTransaction = RouterTransaction(controller)
+  }
+}
+
+fun Controller.asTransaction(
+  popChangeHandler: ControllerChangeHandler? = null,
+  pushChangeHandler: ControllerChangeHandler? = null
+): RouterTransaction {
+  return RouterTransaction.with(this)
+    .pushChangeHandler(pushChangeHandler)
+    .popChangeHandler(popChangeHandler)
+}
@@ -1,9 +1,11 @@
 package com.bluelinelabs.conductor.changehandler;

 import android.animation.Animator;
+import android.animation.Animator.AnimatorListener;
 import android.animation.AnimatorListenerAdapter;
 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.ViewTreeObserver;
@@ -19,22 +21,28 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
    private static final String KEY_DURATION = "AnimatorChangeHandler.duration";
    private static final String KEY_REMOVES_FROM_ON_PUSH = "AnimatorChangeHandler.removesFromViewOnPush";

+    @SuppressWarnings("WeakerAccess")
    public static final long DEFAULT_ANIMATION_DURATION = -1;

    private long animationDuration;
-    private boolean removesFromViewOnPush;
-    private boolean canceled;
-    private boolean needsImmediateCompletion;
-    private Animator animator;
+    boolean removesFromViewOnPush;
+    boolean canceled;
+    boolean needsImmediateCompletion;
+    private boolean completed;
+    Animator animator;
+    private OnAnimationReadyOrAbortedListener onAnimationReadyOrAbortedListener;

+    @SuppressWarnings("WeakerAccess")
    public AnimatorChangeHandler() {
        this(DEFAULT_ANIMATION_DURATION, true);
    }

+    @SuppressWarnings("WeakerAccess")
    public AnimatorChangeHandler(boolean removesFromViewOnPush) {
        this(DEFAULT_ANIMATION_DURATION, removesFromViewOnPush);
    }

+    @SuppressWarnings("WeakerAccess")
    public AnimatorChangeHandler(long duration) {
        this(duration, true);
    }
@@ -59,12 +67,14 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
    }

    @Override
-    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, Controller newTop) {
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
        super.onAbortPush(newHandler, newTop);

        canceled = true;
        if (animator != null) {
            animator.cancel();
+        } else if (onAnimationReadyOrAbortedListener != null) {
+            onAnimationReadyOrAbortedListener.onReadyOrAborted();
        }
    }

@@ -74,7 +84,9 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {

        needsImmediateCompletion = true;
        if (animator != null) {
-            animator.cancel();
+            animator.end();
+        } else if (onAnimationReadyOrAbortedListener != null) {
+            onAnimationReadyOrAbortedListener.onReadyOrAborted();
        }
    }

@@ -91,12 +103,13 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
     * Should be overridden to return the Animator to use while replacing Views.
     *
     * @param container The container these Views are hosted in.
-     * @param from The previous View in the container, if any.
-     * @param to The next View that should be put in the container, if any.
+     * @param from The previous View in the container or {@code null} if there was no Controller before this transition
+     * @param to The next View that should be put in the container or {@code null} if no Controller is being transitioned to
     * @param isPush True if this is a push transaction, false if it's a pop.
     * @param toAddedToContainer True if the "to" view was added to the container as a part of this ChangeHandler. False if it was already in the hierarchy.
     */
-    protected abstract Animator getAnimator(@NonNull ViewGroup container, View from, View to, boolean isPush, boolean toAddedToContainer);
+    @NonNull
+    protected abstract Animator getAnimator(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, boolean toAddedToContainer);

    /**
     * Will be called after the animation is complete to reset the View that was removed to its pre-animation state.
@@ -104,7 +117,7 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
    protected abstract void resetFromView(@NonNull View from);

    @Override
-    public final void performChange(@NonNull final ViewGroup container, final View from, final View to, final boolean isPush, @NonNull final ControllerChangeCompletedListener changeListener) {
+    public final void performChange(@NonNull final ViewGroup container, @Nullable final View from, @Nullable final View to, final boolean isPush, @NonNull final ControllerChangeCompletedListener changeListener) {
        boolean readyToAnimate = true;
        final boolean addingToView = to != null && to.getParent() == null;

@@ -117,17 +130,8 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {

            if (to.getWidth() <= 0 && to.getHeight() <= 0) {
                readyToAnimate = false;
-                to.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() {
-                    @Override
-                    public boolean onPreDraw() {
-                        final ViewTreeObserver observer = to.getViewTreeObserver();
-                        if (observer.isAlive()) {
-                            observer.removeOnPreDrawListener(this);
-                        }
-                        performAnimation(container, from, to, isPush, addingToView, changeListener);
-                        return true;
-                    }
-                });
+                onAnimationReadyOrAbortedListener = new OnAnimationReadyOrAbortedListener(container, from, to, isPush, true, changeListener);
+                to.getViewTreeObserver().addOnPreDrawListener(onAnimationReadyOrAbortedListener);
            }
        }

@@ -136,9 +140,36 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
        }
    }

-    private void performAnimation(@NonNull final ViewGroup container, final View from, final View to, final boolean isPush, final boolean toAddedToContainer, @NonNull final ControllerChangeCompletedListener changeListener) {
-        if (canceled) {
+    void complete(@NonNull ControllerChangeCompletedListener changeListener, @Nullable AnimatorListener animatorListener) {
+        if (!completed) {
+            completed = true;
            changeListener.onChangeCompleted();
+        }
+
+        if (animator != null) {
+            if (animatorListener != null) {
+                animator.removeListener(animatorListener);
+            }
+            animator.cancel();
+            animator = null;
+        }
+
+        onAnimationReadyOrAbortedListener = null;
+    }
+
+    void performAnimation(@NonNull final ViewGroup container, @Nullable final View from, @Nullable final View to, final boolean isPush, final boolean toAddedToContainer, @NonNull final ControllerChangeCompletedListener changeListener) {
+        if (canceled) {
+            complete(changeListener, null);
+            return;
+        }
+        if (needsImmediateCompletion) {
+            if (from != null && (!isPush || removesFromViewOnPush)) {
+                container.removeView(from);
+            }
+            complete(changeListener, null);
+            if (isPush && from != null) {
+                resetFromView(from);
+            }
            return;
        }

@@ -151,13 +182,15 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
        animator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationCancel(Animator animation) {
-                if (from != null && (!isPush || removesFromViewOnPush) && needsImmediateCompletion) {
-                    container.removeView(from);
+                if (from != null) {
+                    resetFromView(from);
                }

-                changeListener.onChangeCompleted();
-                animator.removeListener(this);
-                animator = null;
+                if (to != null && to.getParent() == container) {
+                    container.removeView(to);
+                }
+
+                complete(changeListener, this);
            }

            @Override
@@ -167,14 +200,11 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
                        container.removeView(from);
                    }

-                    changeListener.onChangeCompleted();
-                    animator.removeListener(this);
+                    complete(changeListener, this);

                    if (isPush && from != null) {
                        resetFromView(from);
                    }
-
-                    animator = null;
                }
            }
        });
@@ -182,4 +212,46 @@ public abstract class AnimatorChangeHandler extends ControllerChangeHandler {
        animator.start();
    }

+    private class OnAnimationReadyOrAbortedListener implements ViewTreeObserver.OnPreDrawListener {
+        @NonNull final ViewGroup container;
+        @Nullable final View from;
+        @Nullable final View to;
+        final boolean isPush;
+        final boolean addingToView;
+        @NonNull final ControllerChangeCompletedListener changeListener;
+        private boolean hasRun;
+
+        OnAnimationReadyOrAbortedListener(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, boolean addingToView, @NonNull ControllerChangeCompletedListener changeListener) {
+            this.container = container;
+            this.from = from;
+            this.to = to;
+            this.isPush = isPush;
+            this.addingToView = addingToView;
+            this.changeListener = changeListener;
+        }
+
+        @Override
+        public boolean onPreDraw() {
+            onReadyOrAborted();
+
+            return true;
+        }
+
+        void onReadyOrAborted() {
+            if (!hasRun) {
+                hasRun = true;
+
+                if (to != null) {
+                    final ViewTreeObserver observer = to.getViewTreeObserver();
+                    if (observer.isAlive()) {
+                        observer.removeOnPreDrawListener(this);
+                    }
+                }
+
+                performAnimation(container, from, to, isPush, addingToView, changeListener);
+            }
+        }
+
+    }
+
 }
@@ -1,23 +0,0 @@
-package com.bluelinelabs.conductor.changehandler;
-
-import android.annotation.TargetApi;
-import android.os.Build;
-import android.support.annotation.NonNull;
-import android.transition.AutoTransition;
-import android.transition.Transition;
-import android.view.View;
-import android.view.ViewGroup;
-
-/**
- * A change handler that will use an AutoTransition.
- */
-@TargetApi(Build.VERSION_CODES.LOLLIPOP)
-public class AutoTransitionChangeHandler extends TransitionChangeHandler {
-
-    @Override
-    @NonNull
-    protected Transition getTransition(@NonNull ViewGroup container, View from, View to, boolean isPush) {
-        return new AutoTransition();
-    }
-
-}
@@ -3,10 +3,13 @@ package com.bluelinelabs.conductor.changehandler;
 import android.animation.Animator;
 import android.animation.AnimatorSet;
 import android.animation.ObjectAnimator;
-import android.support.annotation.NonNull;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.view.View;
 import android.view.ViewGroup;

+import com.bluelinelabs.conductor.ControllerChangeHandler;
+
 /**
 * An {@link AnimatorChangeHandler} that will cross fade two views
 */
@@ -26,14 +29,15 @@ public class FadeChangeHandler extends AnimatorChangeHandler {
        super(duration, removesFromViewOnPush);
    }

-    @Override
-    protected Animator getAnimator(@NonNull ViewGroup container, View from, View to, boolean isPush, boolean toAddedToContainer) {
+    @Override @NonNull
+    protected Animator getAnimator(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, boolean toAddedToContainer) {
        AnimatorSet animator = new AnimatorSet();
-        if (to != null && toAddedToContainer) {
-            animator.play(ObjectAnimator.ofFloat(to, View.ALPHA, 0, 1));
+        if (to != null) {
+            float start = toAddedToContainer ? 0 : to.getAlpha();
+            animator.play(ObjectAnimator.ofFloat(to, View.ALPHA, start, 1));
        }

-        if (from != null) {
+        if (from != null && (!isPush || removesFromViewOnPush())) {
            animator.play(ObjectAnimator.ofFloat(from, View.ALPHA, 0));
        }

@@ -44,4 +48,10 @@ public class FadeChangeHandler extends AnimatorChangeHandler {
    protected void resetFromView(@NonNull View from) {
        from.setAlpha(1);
    }
+
+    @Override @NonNull
+    public ControllerChangeHandler copy() {
+        return new FadeChangeHandler(getAnimationDuration(), removesFromViewOnPush());
+    }
+
 }
@@ -3,10 +3,13 @@ package com.bluelinelabs.conductor.changehandler;
 import android.animation.Animator;
 import android.animation.AnimatorSet;
 import android.animation.ObjectAnimator;
-import android.support.annotation.NonNull;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.view.View;
 import android.view.ViewGroup;

+import com.bluelinelabs.conductor.ControllerChangeHandler;
+
 /**
 * An {@link AnimatorChangeHandler} that will slide the views left or right, depending on if it's a push or pop.
 */
@@ -26,8 +29,8 @@ public class HorizontalChangeHandler extends AnimatorChangeHandler {
        super(duration, removesFromViewOnPush);
    }

-    @Override
-    protected Animator getAnimator(@NonNull ViewGroup container, View from, View to, boolean isPush, boolean toAddedToContainer) {
+    @Override @NonNull
+    protected Animator getAnimator(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, boolean toAddedToContainer) {
        AnimatorSet animatorSet = new AnimatorSet();

        if (isPush) {
@@ -42,7 +45,9 @@ public class HorizontalChangeHandler extends AnimatorChangeHandler {
                animatorSet.play(ObjectAnimator.ofFloat(from, View.TRANSLATION_X, from.getWidth()));
            }
            if (to != null) {
-                animatorSet.play(ObjectAnimator.ofFloat(to, View.TRANSLATION_X, -to.getWidth(), 0));
+                // Allow this to have a nice transition when coming off an aborted push animation
+                float fromLeft = from != null ? from.getTranslationX() : 0;
+                animatorSet.play(ObjectAnimator.ofFloat(to, View.TRANSLATION_X, fromLeft - to.getWidth(), 0));
            }
        }

@@ -53,4 +58,10 @@ public class HorizontalChangeHandler extends AnimatorChangeHandler {
    protected void resetFromView(@NonNull View from) {
        from.setTranslationX(0);
    }
+
+    @Override @NonNull
+    public ControllerChangeHandler copy() {
+        return new HorizontalChangeHandler(getAnimationDuration(), removesFromViewOnPush());
+    }
+
 }
@@ -1,7 +1,8 @@
 package com.bluelinelabs.conductor.changehandler;

 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.view.View;
 import android.view.View.OnAttachStateChangeListener;
 import android.view.ViewGroup;
@@ -44,7 +45,7 @@ public class SimpleSwapChangeHandler extends ControllerChangeHandler implements
    }

    @Override
-    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, Controller newTop) {
+    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, @Nullable Controller newTop) {
        super.onAbortPush(newHandler, newTop);

        canceled = true;
@@ -62,7 +63,7 @@ public class SimpleSwapChangeHandler extends ControllerChangeHandler implements
    }

    @Override
-    public void performChange(@NonNull ViewGroup container, View from, View to, boolean isPush, @NonNull ControllerChangeCompletedListener changeListener) {
+    public void performChange(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, @NonNull ControllerChangeCompletedListener changeListener) {
        if (!canceled) {
            if (from != null && (!isPush || removesFromViewOnPush)) {
                container.removeView(from);
@@ -89,7 +90,7 @@ public class SimpleSwapChangeHandler extends ControllerChangeHandler implements
    }

    @Override
-    public void onViewAttachedToWindow(View v) {
+    public void onViewAttachedToWindow(@NonNull View v) {
        v.removeOnAttachStateChangeListener(this);

        if (changeListener != null) {
@@ -100,5 +101,15 @@ public class SimpleSwapChangeHandler extends ControllerChangeHandler implements
    }

    @Override
-    public void onViewDetachedFromWindow(View v) { }
+    public void onViewDetachedFromWindow(@NonNull View v) { }
+
+    @Override @NonNull
+    public ControllerChangeHandler copy() {
+        return new SimpleSwapChangeHandler(removesFromViewOnPush());
+    }
+
+    @Override
+    public boolean isReusable() {
+        return true;
+    }
 }
@@ -1,83 +0,0 @@
-package com.bluelinelabs.conductor.changehandler;
-
-import android.annotation.TargetApi;
-import android.os.Build;
-import android.support.annotation.NonNull;
-import android.transition.Transition;
-import android.transition.Transition.TransitionListener;
-import android.transition.TransitionManager;
-import android.view.View;
-import android.view.ViewGroup;
-
-import com.bluelinelabs.conductor.Controller;
-import com.bluelinelabs.conductor.ControllerChangeHandler;
-
-/**
- * A base {@link ControllerChangeHandler} that facilitates using {@link android.transition.Transition}s to replace Controller Views.
- */
-@TargetApi(Build.VERSION_CODES.LOLLIPOP)
-public abstract class TransitionChangeHandler extends ControllerChangeHandler {
-
-    private boolean canceled;
-
-    /**
-     * Should be overridden to return the Transition to use while replacing Views.
-     *
-     * @param container The container these Views are hosted in.
-     * @param from The previous View in the container, if any.
-     * @param to The next View that should be put in the container, if any.
-     * @param isPush True if this is a push transaction, false if it's a pop.
-     */
-    @NonNull
-    protected abstract Transition getTransition(@NonNull ViewGroup container, View from, View to, boolean isPush);
-
-    @Override
-    public void onAbortPush(@NonNull ControllerChangeHandler newHandler, Controller newTop) {
-        super.onAbortPush(newHandler, newTop);
-
-        canceled = true;
-    }
-
-    @Override
-    public void performChange(@NonNull final ViewGroup container, View from, View to, boolean isPush, @NonNull final ControllerChangeCompletedListener changeListener) {
-        if (canceled) {
-            changeListener.onChangeCompleted();
-            return;
-        }
-
-        Transition transition = getTransition(container, from, to, isPush);
-        transition.addListener(new TransitionListener() {
-            @Override
-            public void onTransitionStart(Transition transition) { }
-
-            @Override
-            public void onTransitionEnd(Transition transition) {
-                changeListener.onChangeCompleted();
-            }
-
-            @Override
-            public void onTransitionCancel(Transition transition) {
-                changeListener.onChangeCompleted();
-            }
-
-            @Override
-            public void onTransitionPause(Transition transition) { }
-
-            @Override
-            public void onTransitionResume(Transition transition) { }
-        });
-
-        TransitionManager.beginDelayedTransition(container, transition);
-        if (from != null) {
-            container.removeView(from);
-        }
-        if (to != null) {
-            container.addView(to);
-        }
-    }
-
-    @Override
-    public final boolean removesFromViewOnPush() {
-        return true;
-    }
-}
@@ -1,88 +0,0 @@
-package com.bluelinelabs.conductor.changehandler;
-
-import android.os.Build;
-import android.os.Bundle;
-import android.support.annotation.NonNull;
-import android.view.View;
-import android.view.ViewGroup;
-
-import com.bluelinelabs.conductor.ControllerChangeHandler;
-import com.bluelinelabs.conductor.internal.ClassUtils;
-
-/**
- * A base {@link ControllerChangeHandler} that facilitates using {@link android.transition.Transition}s to replace Controller Views.
- * If the target device is running on a version of Android that doesn't support transitions, a fallback {@link ControllerChangeHandler} will be used.
- */
-public class TransitionChangeHandlerCompat extends ControllerChangeHandler {
-
-    private static final String KEY_TRANSITION_HANDLER_CLASS = "TransitionChangeHandlerCompat.transitionChangeHandler.class";
-    private static final String KEY_FALLBACK_HANDLER_CLASS = "TransitionChangeHandlerCompat.fallbackChangeHandler.class";
-    private static final String KEY_TRANSITION_HANDLER_STATE = "TransitionChangeHandlerCompat.transitionChangeHandler.state";
-    private static final String KEY_FALLBACK_HANDLER_STATE = "TransitionChangeHandlerCompat.fallbackChangeHandler.state";
-
-    private TransitionChangeHandler transitionChangeHandler;
-    private ControllerChangeHandler fallbackChangeHandler;
-
-    public TransitionChangeHandlerCompat() { }
-
-    /**
-     * Constructor that takes a {@link TransitionChangeHandler} for use with compatible devices, as well as a fallback
-     * {@link ControllerChangeHandler} for use with older devices.
-     *
-     * @param transitionChangeHandler The change handler that will be used on API 21 and above
-     * @param fallbackChangeHandler The change handler that will be used on APIs below 21
-     */
-    public TransitionChangeHandlerCompat(TransitionChangeHandler transitionChangeHandler, ControllerChangeHandler fallbackChangeHandler) {
-        this.transitionChangeHandler = transitionChangeHandler;
-        this.fallbackChangeHandler = fallbackChangeHandler;
-    }
-
-    @Override
-    public void performChange(@NonNull final ViewGroup container, View from, View to, boolean isPush, @NonNull final ControllerChangeCompletedListener changeListener) {
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
-            transitionChangeHandler.performChange(container, from, to, isPush, changeListener);
-        } else {
-            fallbackChangeHandler.performChange(container, from, to, isPush, changeListener);
-        }
-    }
-
-    @Override
-    public void saveToBundle(@NonNull Bundle bundle) {
-        super.saveToBundle(bundle);
-
-        bundle.putString(KEY_TRANSITION_HANDLER_CLASS, transitionChangeHandler.getClass().getName());
-        bundle.putString(KEY_FALLBACK_HANDLER_CLASS, fallbackChangeHandler.getClass().getName());
-
-        Bundle transitionBundle = new Bundle();
-        transitionChangeHandler.saveToBundle(transitionBundle);
-        bundle.putBundle(KEY_TRANSITION_HANDLER_STATE, transitionBundle);
-
-        Bundle fallbackBundle = new Bundle();
-        fallbackChangeHandler.saveToBundle(fallbackBundle);
-        bundle.putBundle(KEY_FALLBACK_HANDLER_STATE, fallbackBundle);
-    }
-
-    @Override
-    public void restoreFromBundle(@NonNull Bundle bundle) {
-        super.restoreFromBundle(bundle);
-
-        String transitionClassName = bundle.getString(KEY_TRANSITION_HANDLER_CLASS);
-        transitionChangeHandler = ClassUtils.newInstance(transitionClassName);
-        //noinspection ConstantConditions
-        transitionChangeHandler.restoreFromBundle(bundle.getBundle(KEY_TRANSITION_HANDLER_STATE));
-
-        String fallbackClassName = bundle.getString(KEY_FALLBACK_HANDLER_CLASS);
-        fallbackChangeHandler = ClassUtils.newInstance(fallbackClassName);
-        //noinspection ConstantConditions
-        fallbackChangeHandler.restoreFromBundle(bundle.getBundle(KEY_FALLBACK_HANDLER_STATE));
-    }
-
-    @Override
-    public boolean removesFromViewOnPush() {
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
-            return transitionChangeHandler.removesFromViewOnPush();
-        } else {
-            return fallbackChangeHandler.removesFromViewOnPush();
-        }
-    }
-}
@@ -3,10 +3,13 @@ package com.bluelinelabs.conductor.changehandler;
 import android.animation.Animator;
 import android.animation.AnimatorSet;
 import android.animation.ObjectAnimator;
-import android.support.annotation.NonNull;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.view.View;
 import android.view.ViewGroup;

+import com.bluelinelabs.conductor.ControllerChangeHandler;
+
 import java.util.ArrayList;
 import java.util.List;

@@ -30,8 +33,8 @@ public class VerticalChangeHandler extends AnimatorChangeHandler {
        super(duration, removesFromViewOnPush);
    }

-    @Override
-    protected Animator getAnimator(@NonNull ViewGroup container, View from, View to, boolean isPush, boolean toAddedToContainer) {
+    @Override @NonNull
+    protected Animator getAnimator(@NonNull ViewGroup container, @Nullable View from, @Nullable View to, boolean isPush, boolean toAddedToContainer) {
        AnimatorSet animator = new AnimatorSet();
        List<Animator> viewAnimators = new ArrayList<>();

@@ -48,4 +51,9 @@ public class VerticalChangeHandler extends AnimatorChangeHandler {
    @Override
    protected void resetFromView(@NonNull View from) { }

+    @Override @NonNull
+    public ControllerChangeHandler copy() {
+        return new VerticalChangeHandler(getAnimationDuration(), removesFromViewOnPush());
+    }
+
 }
@@ -1,16 +1,13 @@
 package com.bluelinelabs.conductor.internal;

+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import android.text.TextUtils;

 public class ClassUtils {

-    @SuppressWarnings("unchecked")
-    public static <T> Class<? extends T> classForName(String className) {
-        return classForName(className, true);
-    }
-
-    @SuppressWarnings("unchecked")
-    public static <T> Class<? extends T> classForName(String className, boolean allowEmptyName) {
+    @Nullable @SuppressWarnings("unchecked")
+    public static <T> Class<? extends T> classForName(@NonNull String className, boolean allowEmptyName) {
        if (allowEmptyName && TextUtils.isEmpty(className)) {
            return null;
        }
@@ -22,10 +19,10 @@ public class ClassUtils {
        }
    }

-    @SuppressWarnings("unchecked")
-    public static <T> T newInstance(String className) {
+    @Nullable @SuppressWarnings("unchecked")
+    public static <T> T newInstance(@NonNull String className) {
        try {
-            Class<? extends T> cls = classForName(className);
+            Class<? extends T> cls = classForName(className, true);
            return cls != null ? cls.newInstance() : null;
        } catch (Exception e) {
            throw new RuntimeException("An exception occurred while creating a new instance of " + className + ". " + e.getMessage());
@@ -6,15 +6,20 @@ import android.app.Application.ActivityLifecycleCallbacks;
 import android.app.Fragment;
 import android.content.Context;
 import android.content.Intent;
+import android.content.IntentSender;
 import android.os.Build;
 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import android.os.Parcel;
+import android.os.Parcelable;
 import android.util.SparseArray;
 import android.view.Menu;
 import android.view.MenuInflater;
 import android.view.MenuItem;
 import android.view.ViewGroup;

+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
 import com.bluelinelabs.conductor.ActivityHostedRouter;
 import com.bluelinelabs.conductor.Router;

@@ -27,6 +32,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

    private static final String FRAGMENT_TAG = "LifecycleHandler";

+    private static final String KEY_PENDING_PERMISSION_REQUESTS = "LifecycleHandler.pendingPermissionRequests";
    private static final String KEY_PERMISSION_REQUEST_CODES = "LifecycleHandler.permissionRequests";
    private static final String KEY_ACTIVITY_REQUEST_CODES = "LifecycleHandler.activityRequests";
    private static final String KEY_ROUTER_STATE_PREFIX = "LifecycleHandler.routerState";
@@ -34,9 +40,13 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    private Activity activity;
    private boolean hasRegisteredCallbacks;
    private boolean destroyed;
+    private boolean attached;
+    private boolean hasPreparedForHostDetach;

+    private static final Map<Activity, LifecycleHandler> activeLifecycleHandlers = new HashMap<>();
    private SparseArray<String> permissionRequestMap = new SparseArray<>();
    private SparseArray<String> activityRequestMap = new SparseArray<>();
+    private ArrayList<PendingPermissionRequest> pendingPermissionRequests = new ArrayList<>();

    private final Map<Integer, ActivityHostedRouter> routerMap = new HashMap<>();

@@ -45,15 +55,20 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
        setHasOptionsMenu(true);
    }

-    private static LifecycleHandler findInActivity(Activity activity) {
-        LifecycleHandler lifecycleHandler = (LifecycleHandler)activity.getFragmentManager().findFragmentByTag(FRAGMENT_TAG);
+    @Nullable
+    private static LifecycleHandler findInActivity(@NonNull Activity activity) {
+        LifecycleHandler lifecycleHandler = activeLifecycleHandlers.get(activity);
+        if (lifecycleHandler == null) {
+            lifecycleHandler = (LifecycleHandler)activity.getFragmentManager().findFragmentByTag(FRAGMENT_TAG);
+        }
        if (lifecycleHandler != null) {
            lifecycleHandler.registerActivityListener(activity);
        }
        return lifecycleHandler;
    }

-    public static LifecycleHandler install(Activity activity) {
+    @NonNull
+    public static LifecycleHandler install(@NonNull Activity activity) {
        LifecycleHandler lifecycleHandler = findInActivity(activity);
        if (lifecycleHandler == null) {
            lifecycleHandler = new LifecycleHandler();
@@ -63,7 +78,8 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
        return lifecycleHandler;
    }

-    public Router getRouter(ViewGroup container, Bundle savedInstanceState) {
+    @NonNull
+    public Router getRouter(@NonNull ViewGroup container, @Nullable Bundle savedInstanceState) {
        ActivityHostedRouter router = routerMap.get(getRouterHashKey(container));
        if (router == null) {
            router = new ActivityHostedRouter();
@@ -83,24 +99,31 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
        return router;
    }

+    @NonNull
    public List<Router> getRouters() {
-        return new ArrayList<Router>(routerMap.values());
+        return new ArrayList<>(routerMap.values());
    }

+    @Nullable
    public Activity getLifecycleActivity() {
        return activity;
    }

-    private static int getRouterHashKey(ViewGroup viewGroup) {
+    private static int getRouterHashKey(@NonNull ViewGroup viewGroup) {
        return viewGroup.getId();
    }

-    private void registerActivityListener(Activity activity) {
+    private void registerActivityListener(@NonNull Activity activity) {
        this.activity = activity;

        if (!hasRegisteredCallbacks) {
            hasRegisteredCallbacks = true;
            activity.getApplication().registerActivityLifecycleCallbacks(this);
+
+            // Since Fragment transactions are async, we have to keep an <Activity, LifecycleHandler> map in addition
+            // to trying to find the LifecycleHandler fragment in the Activity to handle the case of the developer
+            // trying to immediately get > 1 router in the same Activity. See issue #299.
+            activeLifecycleHandlers.put(activity, this);
        }
    }

@@ -110,10 +133,13 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

        if (savedInstanceState != null) {
            StringSparseArrayParceler permissionParcel = savedInstanceState.getParcelable(KEY_PERMISSION_REQUEST_CODES);
-            permissionRequestMap = permissionParcel != null ? permissionParcel.getStringSparseArray() : null;
+            permissionRequestMap = permissionParcel != null ? permissionParcel.getStringSparseArray() : new SparseArray<>();

            StringSparseArrayParceler activityParcel = savedInstanceState.getParcelable(KEY_ACTIVITY_REQUEST_CODES);
-            activityRequestMap = activityParcel != null ? activityParcel.getStringSparseArray() : null;
+            activityRequestMap = activityParcel != null ? activityParcel.getStringSparseArray() : new SparseArray<>();
+
+            ArrayList<PendingPermissionRequest> pendingRequests = savedInstanceState.getParcelableArrayList(KEY_PENDING_PERMISSION_REQUESTS);
+            pendingPermissionRequests = pendingRequests != null ? pendingRequests : new ArrayList<>();
        }
    }

@@ -123,6 +149,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

        outState.putParcelable(KEY_PERMISSION_REQUEST_CODES, new StringSparseArrayParceler(permissionRequestMap));
        outState.putParcelable(KEY_ACTIVITY_REQUEST_CODES, new StringSparseArrayParceler(activityRequestMap));
+        outState.putParcelableArrayList(KEY_PENDING_PERMISSION_REQUESTS, pendingPermissionRequests);
    }

    @Override
@@ -131,37 +158,55 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

        if (activity != null) {
            activity.getApplication().unregisterActivityLifecycleCallbacks(this);
+            activeLifecycleHandlers.remove(activity);
            destroyRouters();
            activity = null;
        }
    }

-    @SuppressWarnings("deprecation")
    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        destroyed = false;
+        setAttached();
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        destroyed = false;
+        setAttached();
    }

    @Override
    public void onDetach() {
        super.onDetach();

+        attached = false;
        destroyRouters();
    }

+    private void setAttached() {
+        if (!attached) {
+            attached = true;
+
+            for (int i = pendingPermissionRequests.size() - 1; i >= 0; i--) {
+                PendingPermissionRequest request = pendingPermissionRequests.remove(i);
+                requestPermissions(request.instanceId, request.permissions, request.requestCode);
+            }
+        }
+
+        for (ActivityHostedRouter router : new ArrayList<>(routerMap.values())) {
+            router.onContextAvailable();
+        }
+    }
+
    private void destroyRouters() {
        if (!destroyed) {
            destroyed = true;

            if (activity != null) {
-                for (Router router : routerMap.values()) {
+                for (Router router : getRouters()) {
                    router.onActivityDestroyed(activity);
                }
            }
@@ -174,7 +219,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

        String instanceId = activityRequestMap.get(requestCode);
        if (instanceId != null) {
-            for (Router router : routerMap.values()) {
+            for (Router router : getRouters()) {
                router.onActivityResult(instanceId, requestCode, resultCode, data);
            }
        }
@@ -186,7 +231,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

        String instanceId = permissionRequestMap.get(requestCode);
        if (instanceId != null) {
-            for (Router router : routerMap.values()) {
+            for (Router router : getRouters()) {
                router.onRequestPermissionsResult(instanceId, requestCode, permissions, grantResults);
            }
        }
@@ -194,7 +239,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb

    @Override
    public boolean shouldShowRequestPermissionRationale(@NonNull String permission) {
-        for (Router router : routerMap.values()) {
+        for (Router router : getRouters()) {
            Boolean handled = router.handleRequestedPermission(permission);
            if (handled != null) {
                return handled;
@@ -207,7 +252,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        super.onCreateOptionsMenu(menu, inflater);

-        for (Router router : routerMap.values()) {
+        for (Router router : getRouters()) {
            router.onCreateOptionsMenu(menu, inflater);
        }
    }
@@ -216,14 +261,14 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    public void onPrepareOptionsMenu(Menu menu) {
        super.onPrepareOptionsMenu(menu);

-        for (Router router : routerMap.values()) {
+        for (Router router : getRouters()) {
            router.onPrepareOptionsMenu(menu);
        }
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
-        for (Router router : routerMap.values()) {
+        for (Router router : getRouters()) {
            if (router.onOptionsItemSelected(item)) {
                return true;
            }
@@ -232,11 +277,11 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
        return super.onOptionsItemSelected(item);
    }

-    public void registerForActivityResult(String instanceId, int requestCode) {
+    public void registerForActivityResult(@NonNull String instanceId, int requestCode) {
        activityRequestMap.put(requestCode, instanceId);
    }

-    public void unregisterForActivityResults(String instanceId) {
+    public void unregisterForActivityResults(@NonNull String instanceId) {
        for (int i = activityRequestMap.size() - 1; i >= 0; i--) {
            if (instanceId.equals(activityRequestMap.get(activityRequestMap.keyAt(i)))) {
                activityRequestMap.removeAt(i);
@@ -244,33 +289,51 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
        }
    }

-    public void startActivityForResult(String instanceId, Intent intent, int requestCode) {
+    public void startActivityForResult(@NonNull String instanceId, @NonNull Intent intent, int requestCode) {
        registerForActivityResult(instanceId, requestCode);
        startActivityForResult(intent, requestCode);
    }

-    public void startActivityForResult(String instanceId, Intent intent, int requestCode, Bundle options) {
+    public void startActivityForResult(@NonNull String instanceId, @NonNull Intent intent, int requestCode, @Nullable Bundle options) {
        registerForActivityResult(instanceId, requestCode);
        startActivityForResult(intent, requestCode, options);
    }

+    @TargetApi(Build.VERSION_CODES.N)
+    public void startIntentSenderForResult(@NonNull String instanceId, @NonNull IntentSender intent, int requestCode,
+                                           @Nullable Intent fillInIntent, int flagsMask, int flagsValues, int extraFlags,
+                                           @Nullable Bundle options) throws IntentSender.SendIntentException {
+        registerForActivityResult(instanceId, requestCode);
+        startIntentSenderForResult(intent, requestCode, fillInIntent, flagsMask, flagsValues, extraFlags, options);
+    }
+
    @TargetApi(Build.VERSION_CODES.M)
-    public void requestPermissions(String instanceId, String[] permissions, int requestCode) {
-        permissionRequestMap.put(requestCode, instanceId);
-        requestPermissions(permissions, requestCode);
+    public void requestPermissions(@NonNull String instanceId, @NonNull String[] permissions, int requestCode) {
+        if (attached) {
+            permissionRequestMap.put(requestCode, instanceId);
+            requestPermissions(permissions, requestCode);
+        } else {
+            pendingPermissionRequests.add(new PendingPermissionRequest(instanceId, permissions, requestCode));
+        }
    }

    @Override
    public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        if (this.activity == null && findInActivity(activity) == LifecycleHandler.this) {
            this.activity = activity;
+
+            for (ActivityHostedRouter router : new ArrayList<>(routerMap.values())) {
+                router.onContextAvailable();
+            }
        }
    }

    @Override
    public void onActivityStarted(Activity activity) {
        if (this.activity == activity) {
-            for (Router router : routerMap.values()) {
+            hasPreparedForHostDetach = false;
+
+            for (Router router : getRouters()) {
                router.onActivityStarted(activity);
            }
        }
@@ -279,7 +342,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    @Override
    public void onActivityResumed(Activity activity) {
        if (this.activity == activity) {
-            for (Router router : routerMap.values()) {
+            for (Router router : getRouters()) {
                router.onActivityResumed(activity);
            }
        }
@@ -288,7 +351,7 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    @Override
    public void onActivityPaused(Activity activity) {
        if (this.activity == activity) {
-            for (Router router : routerMap.values()) {
+            for (Router router : getRouters()) {
                router.onActivityPaused(activity);
            }
        }
@@ -297,7 +360,9 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    @Override
    public void onActivityStopped(Activity activity) {
        if (this.activity == activity) {
-            for (Router router : routerMap.values()) {
+            prepareForHostDetachIfNeeded();
+
+            for (Router router : getRouters()) {
                router.onActivityStopped(activity);
            }
        }
@@ -306,7 +371,9 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
        if (this.activity == activity) {
-            for (Router router : routerMap.values()) {
+            prepareForHostDetachIfNeeded();
+
+            for (Router router : getRouters()) {
                Bundle bundle = new Bundle();
                router.saveInstanceState(bundle);
                outState.putBundle(KEY_ROUTER_STATE_PREFIX + router.getContainerId(), bundle);
@@ -315,5 +382,60 @@ public class LifecycleHandler extends Fragment implements ActivityLifecycleCallb
    }

    @Override
-    public void onActivityDestroyed(Activity activity) { }
+    public void onActivityDestroyed(Activity activity) {
+        activeLifecycleHandlers.remove(activity);
+    }
+
+    private void prepareForHostDetachIfNeeded() {
+        if (!hasPreparedForHostDetach) {
+            hasPreparedForHostDetach = true;
+
+            for (Router router : getRouters()) {
+                router.prepareForHostDetach();
+            }
+        }
+    }
+
+    private static class PendingPermissionRequest implements Parcelable {
+        final String instanceId;
+        final String[] permissions;
+        final int requestCode;
+
+        PendingPermissionRequest(@NonNull String instanceId, @NonNull String[] permissions, int requestCode) {
+            this.instanceId = instanceId;
+            this.permissions = permissions;
+            this.requestCode = requestCode;
+        }
+
+        PendingPermissionRequest(Parcel in) {
+            instanceId = in.readString();
+            permissions = in.createStringArray();
+            requestCode = in.readInt();
+        }
+
+        @Override
+        public int describeContents() {
+            return 0;
+        }
+
+        @Override
+        public void writeToParcel(Parcel out, int flags) {
+            out.writeString(instanceId);
+            out.writeStringArray(permissions);
+            out.writeInt(requestCode);
+        }
+
+        public static final Parcelable.Creator<PendingPermissionRequest> CREATOR = new Parcelable.Creator<PendingPermissionRequest>() {
+            @Override
+            public PendingPermissionRequest createFromParcel(Parcel in) {
+                return new PendingPermissionRequest(in);
+            }
+
+            @Override
+            public PendingPermissionRequest[] newArray(int size) {
+                return new PendingPermissionRequest[size];
+            }
+        };
+
+    }
 }
@@ -1,16 +0,0 @@
-package com.bluelinelabs.conductor.internal;
-
-import android.support.annotation.NonNull;
-import android.view.View;
-import android.view.ViewGroup;
-
-import com.bluelinelabs.conductor.ControllerChangeHandler;
-
-public class NoOpControllerChangeHandler extends ControllerChangeHandler {
-
-    @Override
-    public void performChange(@NonNull ViewGroup container, @NonNull View from, @NonNull View to, boolean isPush, @NonNull ControllerChangeCompletedListener changeListener) {
-        changeListener.onChangeCompleted();
-    }
-
-}
@@ -0,0 +1,22 @@
+package com.bluelinelabs.conductor.internal
+
+import android.view.View
+import android.view.ViewGroup
+import com.bluelinelabs.conductor.ControllerChangeHandler
+
+class NoOpControllerChangeHandler : ControllerChangeHandler() {
+
+  override fun performChange(
+    container: ViewGroup,
+    from: View?,
+    to: View?,
+    isPush: Boolean,
+    changeListener: ControllerChangeCompletedListener
+  ) {
+    changeListener.onChangeCompleted()
+  }
+
+  override fun copy(): ControllerChangeHandler = NoOpControllerChangeHandler()
+
+  override fun isReusable() = true
+}
@@ -1,5 +0,0 @@
-package com.bluelinelabs.conductor.internal;
-
-public interface RouterRequiringFunc {
-    void execute();
-}
@@ -0,0 +1,9 @@
+package com.bluelinelabs.conductor.internal
+
+import androidx.annotation.RestrictTo
+import androidx.annotation.RestrictTo.Scope.LIBRARY_GROUP
+
+@RestrictTo(LIBRARY_GROUP)
+interface RouterRequiringFunc {
+  fun execute()
+}
@@ -2,17 +2,18 @@ package com.bluelinelabs.conductor.internal;

 import android.os.Parcel;
 import android.os.Parcelable;
+import androidx.annotation.NonNull;
 import android.util.SparseArray;

 public class StringSparseArrayParceler implements Parcelable {

    private final SparseArray<String> stringSparseArray;

-    public StringSparseArrayParceler(SparseArray<String> stringSparseArray) {
+    public StringSparseArrayParceler(@NonNull SparseArray<String> stringSparseArray) {
        this.stringSparseArray = stringSparseArray;
    }

-    private StringSparseArrayParceler(Parcel in) {
+    StringSparseArrayParceler(@NonNull Parcel in) {
        stringSparseArray = new SparseArray<>();

        final int size = in.readInt();
@@ -22,14 +23,17 @@ public class StringSparseArrayParceler implements Parcelable {
        }
    }

+    @NonNull
    public SparseArray<String> getStringSparseArray() {
        return stringSparseArray;
    }

+    @Override
    public int describeContents() {
        return 0;
    }

+    @Override
    public void writeToParcel(Parcel out, int flags) {
        final int size = stringSparseArray.size();

@@ -44,10 +48,12 @@ public class StringSparseArrayParceler implements Parcelable {
    }

    public static final Parcelable.Creator<StringSparseArrayParceler> CREATOR = new Parcelable.Creator<StringSparseArrayParceler>() {
+        @Override
        public StringSparseArrayParceler createFromParcel(Parcel in) {
            return new StringSparseArrayParceler(in);
        }

+        @Override
        public StringSparseArrayParceler[] newArray(int size) {
            return new StringSparseArrayParceler[size];
        }
@@ -0,0 +1,17 @@
+@file:JvmName("ThreadUtils")
+
+package com.bluelinelabs.conductor.internal
+
+import android.os.Looper
+import android.util.AndroidRuntimeException
+import androidx.annotation.RestrictTo
+import androidx.annotation.RestrictTo.Scope.LIBRARY_GROUP
+
+@RestrictTo(LIBRARY_GROUP)
+internal fun ensureMainThread() {
+  if (Looper.getMainLooper().thread !== Thread.currentThread()) {
+    throw CalledFromWrongThreadException("Methods that affect the view hierarchy can can only be called from the main thread.")
+  }
+}
+
+private class CalledFromWrongThreadException(msg: String?) : AndroidRuntimeException(msg)
@@ -0,0 +1,25 @@
+package com.bluelinelabs.conductor.internal
+
+import android.os.Bundle
+import androidx.annotation.RestrictTo
+import androidx.annotation.RestrictTo.Scope.LIBRARY_GROUP
+
+@RestrictTo(LIBRARY_GROUP)
+class TransactionIndexer {
+
+    private var currentIndex = 0
+
+    fun nextIndex(): Int {
+        return ++currentIndex
+    }
+
+    fun saveInstanceState(outState: Bundle) {
+        outState.putInt(KEY_INDEX, currentIndex)
+    }
+
+    fun restoreInstanceState(savedInstanceState: Bundle) {
+        currentIndex = savedInstanceState.getInt(KEY_INDEX)
+    }
+}
+
+private const val KEY_INDEX = "TransactionIndexer.currentIndex"
@@ -0,0 +1,148 @@
+package com.bluelinelabs.conductor.internal;
+
+import android.view.View;
+import android.view.View.OnAttachStateChangeListener;
+import android.view.ViewGroup;
+
+public class ViewAttachHandler implements OnAttachStateChangeListener {
+
+    private enum ReportedState {
+        VIEW_DETACHED,
+        ACTIVITY_STOPPED,
+        ATTACHED
+    }
+
+    public interface ViewAttachListener {
+        void onAttached();
+        void onDetached(boolean fromActivityStop);
+        void onViewDetachAfterStop();
+    }
+
+    private interface ChildAttachListener {
+        void onAttached();
+    }
+
+    private boolean rootAttached = false;
+    boolean childrenAttached = false;
+    private boolean activityStopped = false;
+    private ReportedState reportedState = ReportedState.VIEW_DETACHED;
+    private ViewAttachListener attachListener;
+    OnAttachStateChangeListener childOnAttachStateChangeListener;
+
+    public ViewAttachHandler(ViewAttachListener attachListener) {
+        this.attachListener = attachListener;
+    }
+
+    @Override
+    public void onViewAttachedToWindow(final View v) {
+        if (rootAttached) {
+            return;
+        }
+
+        rootAttached = true;
+        listenForDeepestChildAttach(v, () -> {
+            childrenAttached = true;
+            reportAttached();
+
+        });
+    }
+
+    @Override
+    public void onViewDetachedFromWindow(View v) {
+        rootAttached = false;
+        if (childrenAttached) {
+            childrenAttached = false;
+            reportDetached(false);
+        }
+    }
+
+    public void listenForAttach(final View view) {
+        view.addOnAttachStateChangeListener(this);
+    }
+
+    public void unregisterAttachListener(View view) {
+        view.removeOnAttachStateChangeListener(this);
+
+        if (childOnAttachStateChangeListener != null && view instanceof ViewGroup) {
+            findDeepestChild((ViewGroup)view).removeOnAttachStateChangeListener(childOnAttachStateChangeListener);
+        }
+    }
+
+    public void onActivityStarted() {
+        activityStopped = false;
+        reportAttached();
+    }
+
+    public void onActivityStopped() {
+        activityStopped = true;
+        reportDetached(true);
+    }
+
+    void reportAttached() {
+        if (rootAttached && childrenAttached && !activityStopped && reportedState != ReportedState.ATTACHED) {
+            reportedState = ReportedState.ATTACHED;
+            attachListener.onAttached();
+        }
+    }
+
+    private void reportDetached(boolean detachedForActivity) {
+        boolean wasDetachedForActivity = reportedState == ReportedState.ACTIVITY_STOPPED;
+
+        if (detachedForActivity) {
+            reportedState = ReportedState.ACTIVITY_STOPPED;
+        } else {
+            reportedState = ReportedState.VIEW_DETACHED;
+        }
+
+        if (wasDetachedForActivity && !detachedForActivity) {
+            attachListener.onViewDetachAfterStop();
+        } else {
+            attachListener.onDetached(detachedForActivity);
+        }
+    }
+
+    private void listenForDeepestChildAttach(final View view, final ChildAttachListener attachListener) {
+        if (!(view instanceof ViewGroup)) {
+            attachListener.onAttached();
+            return;
+        }
+
+        ViewGroup viewGroup = (ViewGroup)view;
+        if (viewGroup.getChildCount() == 0) {
+            attachListener.onAttached();
+            return;
+        }
+
+        childOnAttachStateChangeListener = new OnAttachStateChangeListener() {
+            boolean attached = false;
+
+            @Override
+            public void onViewAttachedToWindow(View v) {
+                if (!attached) {
+                    attached = true;
+                    attachListener.onAttached();
+                    v.removeOnAttachStateChangeListener(this);
+                    childOnAttachStateChangeListener = null;
+                }
+            }
+
+            @Override
+            public void onViewDetachedFromWindow(View v) { }
+        };
+        findDeepestChild(viewGroup).addOnAttachStateChangeListener(childOnAttachStateChangeListener);
+    }
+
+    private View findDeepestChild(ViewGroup viewGroup) {
+        if (viewGroup.getChildCount() == 0) {
+            return viewGroup;
+        }
+
+        View lastChild = viewGroup.getChildAt(viewGroup.getChildCount() - 1);
+        if (lastChild instanceof ViewGroup) {
+            return findDeepestChild((ViewGroup)lastChild);
+        } else {
+            return lastChild;
+        }
+    }
+
+}
@@ -1,72 +0,0 @@
-package com.bluelinelabs.conductor;
-
-import android.os.Bundle;
-import android.support.annotation.IdRes;
-
-import org.robolectric.Robolectric;
-import org.robolectric.util.ActivityController;
-
-public class ActivityProxy {
-
-    private ActivityController<TestActivity> activityController;
-    private AttachFakingFrameLayout view;
-
-    public ActivityProxy() {
-        activityController = Robolectric.buildActivity(TestActivity.class);
-
-        @IdRes int containerId = 4;
-        view = new AttachFakingFrameLayout(activityController.get());
-        view.setId(containerId);
-    }
-
-    public ActivityProxy create(Bundle savedInstanceState) {
-        activityController.create(savedInstanceState);
-        return this;
-    }
-
-    public ActivityProxy start() {
-        activityController.start();
-        view.setAttached(true);
-        return this;
-    }
-
-    public ActivityProxy resume() {
-        activityController.resume();
-        return this;
-    }
-
-    public ActivityProxy pause() {
-        activityController.pause();
-        return this;
-    }
-
-    public ActivityProxy saveInstanceState(Bundle outState) {
-        activityController.saveInstanceState(outState);
-        return this;
-    }
-
-    public ActivityProxy stop() {
-        activityController.stop();
-        view.setAttached(false);
-        return this;
-    }
-
-    public ActivityProxy destroy() {
-        activityController.destroy();
-        return this;
-    }
-
-    public ActivityProxy rotate() {
-        getActivity().isChangingConfigurations = true;
-        getActivity().recreate();
-        return this;
-    }
-
-    public TestActivity getActivity() {
-        return activityController.get();
-    }
-
-    public AttachFakingFrameLayout getView() {
-        return view;
-    }
-}
@@ -1,9 +1,12 @@
 package com.bluelinelabs.conductor;

-import org.junit.Assert;
+import com.bluelinelabs.conductor.util.TestController;
+
 import org.junit.Before;
 import org.junit.Test;

+import static org.junit.Assert.assertEquals;
+
 public class BackstackTests {

    private Backstack backstack;
@@ -15,20 +18,20 @@ public class BackstackTests {

    @Test
    public void testPush() {
-        Assert.assertEquals(0, backstack.size());
+        assertEquals(0, backstack.size());
        backstack.push(RouterTransaction.with(new TestController()));
-        Assert.assertEquals(1, backstack.size());
+        assertEquals(1, backstack.size());
    }

    @Test
    public void testPop() {
        backstack.push(RouterTransaction.with(new TestController()));
        backstack.push(RouterTransaction.with(new TestController()));
-        Assert.assertEquals(2, backstack.size());
+        assertEquals(2, backstack.size());
        backstack.pop();
-        Assert.assertEquals(1, backstack.size());
+        assertEquals(1, backstack.size());
        backstack.pop();
-        Assert.assertEquals(0, backstack.size());
+        assertEquals(0, backstack.size());
    }

    @Test
@@ -37,13 +40,13 @@ public class BackstackTests {
        RouterTransaction transaction2 = RouterTransaction.with(new TestController());

        backstack.push(transaction1);
-        Assert.assertEquals(transaction1, backstack.peek());
+        assertEquals(transaction1, backstack.peek());

        backstack.push(transaction2);
-        Assert.assertEquals(transaction2, backstack.peek());
+        assertEquals(transaction2, backstack.peek());

        backstack.pop();
-        Assert.assertEquals(transaction1, backstack.peek());
+        assertEquals(transaction1, backstack.peek());
    }

    @Test
@@ -56,11 +59,11 @@ public class BackstackTests {
        backstack.push(transaction2);
        backstack.push(transaction3);

-        Assert.assertEquals(3, backstack.size());
+        assertEquals(3, backstack.size());

        backstack.popTo(transaction1);

-        Assert.assertEquals(1, backstack.size());
-        Assert.assertEquals(transaction1, backstack.peek());
+        assertEquals(1, backstack.size());
+        assertEquals(transaction1, backstack.peek());
    }
 }
@@ -2,10 +2,15 @@ package com.bluelinelabs.conductor;

 import com.bluelinelabs.conductor.changehandler.FadeChangeHandler;
 import com.bluelinelabs.conductor.changehandler.HorizontalChangeHandler;
+import com.bluelinelabs.conductor.util.TestController;

-import org.junit.Assert;
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;

+import static org.junit.Assert.assertEquals;
+
+@RunWith(RobolectricTestRunner.class)
 public class ControllerChangeHandlerTests {

    @Test
@@ -21,17 +26,17 @@ public class ControllerChangeHandlerTests {
        ControllerChangeHandler restoredHorizontal = restoredTransaction.pushChangeHandler();
        ControllerChangeHandler restoredFade = restoredTransaction.popChangeHandler();

-        Assert.assertEquals(horizontalChangeHandler.getClass(), restoredHorizontal.getClass());
-        Assert.assertEquals(fadeChangeHandler.getClass(), restoredFade.getClass());
+        assertEquals(horizontalChangeHandler.getClass(), restoredHorizontal.getClass());
+        assertEquals(fadeChangeHandler.getClass(), restoredFade.getClass());

-        HorizontalChangeHandler restoredHorizontalCast = (HorizontalChangeHandler)restoredHorizontal;
-        FadeChangeHandler restoredFadeCast = (FadeChangeHandler)restoredFade;
+        HorizontalChangeHandler restoredHorizontalCast = (HorizontalChangeHandler) restoredHorizontal;
+        FadeChangeHandler restoredFadeCast = (FadeChangeHandler) restoredFade;

-        Assert.assertEquals(horizontalChangeHandler.getAnimationDuration(), restoredHorizontalCast.getAnimationDuration());
-        Assert.assertEquals(horizontalChangeHandler.removesFromViewOnPush(), restoredHorizontalCast.removesFromViewOnPush());
+        assertEquals(horizontalChangeHandler.getAnimationDuration(), restoredHorizontalCast.getAnimationDuration());
+        assertEquals(horizontalChangeHandler.removesFromViewOnPush(), restoredHorizontalCast.removesFromViewOnPush());

-        Assert.assertEquals(fadeChangeHandler.getAnimationDuration(), restoredFadeCast.getAnimationDuration());
-        Assert.assertEquals(fadeChangeHandler.removesFromViewOnPush(), restoredFadeCast.removesFromViewOnPush());
+        assertEquals(fadeChangeHandler.getAnimationDuration(), restoredFadeCast.getAnimationDuration());
+        assertEquals(fadeChangeHandler.removesFromViewOnPush(), restoredFadeCast.removesFromViewOnPush());
    }

 }
@@ -0,0 +1,269 @@
+package com.bluelinelabs.conductor;
+
+import android.os.Bundle;
+import android.view.View;
+
+import androidx.annotation.NonNull;
+
+import com.bluelinelabs.conductor.util.ActivityProxy;
+import com.bluelinelabs.conductor.util.MockChangeHandler;
+import com.bluelinelabs.conductor.util.TestController;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+@RunWith(RobolectricTestRunner.class)
+@Config(manifest = Config.NONE)
+public class ControllerLifecycleActivityReferenceTests {
+
+    private Router router;
+
+    private ActivityProxy activityProxy;
+
+    public void createActivityController(Bundle savedInstanceState, boolean includeStartAndResume) {
+        activityProxy = new ActivityProxy().create(savedInstanceState);
+
+        if (includeStartAndResume) {
+            activityProxy.start().resume();
+        }
+
+        router = Conductor.attachRouter(activityProxy.getActivity(), activityProxy.getView(), savedInstanceState);
+        router.setPopsLastView(true);
+        if (!router.hasRootController()) {
+            router.setRoot(RouterTransaction.with(new TestController()));
+        }
+    }
+
+    @Before
+    public void setup() {
+        createActivityController(null, true);
+    }
+
+    @Test
+    public void testSingleControllerActivityOnPush() {
+        Controller controller = new TestController();
+
+        assertNull(controller.getActivity());
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        controller.addLifecycleListener(listener);
+
+        router.pushController(RouterTransaction.with(controller)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        assertEquals(Collections.singletonList(true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.emptyList(), listener.postDetachReferences);
+        assertEquals(Collections.emptyList(), listener.postDestroyViewReferences);
+        assertEquals(Collections.emptyList(), listener.postDestroyReferences);
+    }
+
+    @Test
+    public void testChildControllerActivityOnPush() {
+        Controller parent = new TestController();
+        router.pushController(RouterTransaction.with(parent)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        TestController child = new TestController();
+
+        assertNull(child.getActivity());
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        child.addLifecycleListener(listener);
+
+        Router childRouter = parent.getChildRouter(parent.getView().findViewById(TestController.VIEW_ID));
+        childRouter.pushController(RouterTransaction.with(child)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        assertEquals(Collections.singletonList(true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.emptyList(), listener.postDetachReferences);
+        assertEquals(Collections.emptyList(), listener.postDestroyViewReferences);
+        assertEquals(Collections.emptyList(), listener.postDestroyReferences);
+    }
+
+    @Test
+    public void testSingleControllerActivityOnPop() {
+        Controller controller = new TestController();
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        controller.addLifecycleListener(listener);
+
+        router.pushController(RouterTransaction.with(controller)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        router.popCurrentController();
+
+        assertEquals(Arrays.asList(true, true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDetachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyReferences);
+    }
+
+    @Test
+    public void testChildControllerActivityOnPop() {
+        Controller parent = new TestController();
+
+        router.pushController(RouterTransaction.with(parent)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        TestController child = new TestController();
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        child.addLifecycleListener(listener);
+
+        Router childRouter = parent.getChildRouter(parent.getView().findViewById(TestController.VIEW_ID));
+        childRouter.setPopsLastView(true);
+        childRouter.pushController(RouterTransaction.with(child)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        childRouter.popCurrentController();
+
+        assertEquals(Arrays.asList(true, true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDetachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyReferences);
+    }
+
+    @Test
+    public void testChildControllerActivityOnParentPop() {
+        Controller parent = new TestController();
+
+        router.pushController(RouterTransaction.with(parent)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        TestController child = new TestController();
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        child.addLifecycleListener(listener);
+
+        Router childRouter = parent.getChildRouter(parent.getView().findViewById(TestController.VIEW_ID));
+        childRouter.setPopsLastView(true);
+        childRouter.pushController(RouterTransaction.with(child)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        router.popCurrentController();
+
+        assertEquals(Collections.singletonList(true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDetachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyReferences);
+    }
+
+    @Test
+    public void testSingleControllerActivityOnDestroy() {
+        Controller controller = new TestController();
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        controller.addLifecycleListener(listener);
+
+        router.pushController(RouterTransaction.with(controller)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        activityProxy.pause().stop(false).destroy();
+
+        assertEquals(Collections.singletonList(true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDetachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyReferences);
+    }
+
+    @Test
+    public void testChildControllerActivityOnDestroy() {
+        Controller parent = new TestController();
+
+        router.pushController(RouterTransaction.with(parent)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        TestController child = new TestController();
+
+        ActivityReferencingLifecycleListener listener = new ActivityReferencingLifecycleListener();
+        child.addLifecycleListener(listener);
+
+        Router childRouter = parent.getChildRouter(parent.getView().findViewById(TestController.VIEW_ID));
+        childRouter.setPopsLastView(true);
+        childRouter.pushController(RouterTransaction.with(child)
+                .pushChangeHandler(MockChangeHandler.defaultHandler())
+                .popChangeHandler(MockChangeHandler.defaultHandler()));
+
+        activityProxy.pause().stop(false).destroy();
+
+        assertEquals(Collections.singletonList(true), listener.changeEndReferences);
+        assertEquals(Collections.singletonList(true), listener.postCreateViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postAttachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDetachReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyViewReferences);
+        assertEquals(Collections.singletonList(true), listener.postDestroyReferences);
+    }
+
+    static class ActivityReferencingLifecycleListener implements Controller.LifecycleListener {
+        final List<Boolean> changeEndReferences = new ArrayList<>();
+        final List<Boolean> postCreateViewReferences = new ArrayList<>();
+        final List<Boolean> postAttachReferences = new ArrayList<>();
+        final List<Boolean> postDetachReferences = new ArrayList<>();
+        final List<Boolean> postDestroyViewReferences = new ArrayList<>();
+        final List<Boolean> postDestroyReferences = new ArrayList<>();
+
+        @Override
+        public void onChangeEnd(@NonNull Controller controller, @NonNull ControllerChangeHandler changeHandler, @NonNull ControllerChangeType changeType) {
+            changeEndReferences.add(controller.getActivity() != null);
+        }
+
+        @Override
+        public void postCreateView(@NonNull Controller controller, @NonNull View view) {
+            postCreateViewReferences.add(controller.getActivity() != null);
+        }
+
+        @Override
+        public void postAttach(@NonNull Controller controller, @NonNull View view) {
+            postAttachReferences.add(controller.getActivity() != null);
+        }
+
+        @Override
+        public void postDetach(@NonNull Controller controller, @NonNull View view) {
+            postDetachReferences.add(controller.getActivity() != null);
+        }
+
+        @Override
+        public void postDestroyView(@NonNull Controller controller) {
+            postDestroyViewReferences.add(controller.getActivity() != null);
+        }
+
+        @Override
+        public void postDestroy(@NonNull Controller controller) {
+            postDestroyReferences.add(controller.getActivity() != null);
+        }
+    }
+
+}
--- a/Show More
+++ b/Show More