RouterStateAdapter now properly restores routers after process death

conductor-modules/viewpager2/src/main/java/com/bluelinelabs/conductor/viewpager2/RouterStateAdapter.kt

@@ -154,7 +154,7 @@ abstract class RouterStateAdapter(private val host: Controller) :
 
   private fun attachRouter(holder: RouterViewHolder, position: Int) {
     val itemId = getItemId(position)
-    val router = host.getChildRouter(holder.container, "$itemId")
+    val router = host.getChildRouter(holder.container, "$itemId", true, false)!!
 
     // This should have already been handled by onViewRecycled, but it seems like this wasn't
     // always reliably called

conductor/src/main/java/com/bluelinelabs/conductor/Controller.java

@@ -9,7 +9,6 @@ import android.content.res.Resources;
 import android.os.Build;
 import android.os.Bundle;
 import android.os.Parcelable;
-import android.text.TextUtils;
 import android.util.SparseArray;
 import android.view.LayoutInflater;
 import android.view.Menu;
@@ -215,6 +214,23 @@ public abstract class Controller {
      */
     @Nullable
     public final Router getChildRouter(@NonNull ViewGroup container, @Nullable String tag, boolean createIfNeeded) {
+        return getChildRouter(container, tag, createIfNeeded, true);
+    }
+
+    /**
+     * Retrieves the child {@link Router} for the given container/tag combination. Note that multiple
+     * routers should not exist in the same container unless a lot of care is taken to maintain order
+     * between them. Avoid using the same container unless you have a great reason to do so (ex: ViewPagers).
+     * The only time this method will return {@code null} is when the child router does not exist prior
+     * to calling this method and the createIfNeeded parameter is set to false.
+     *
+     * @param container              The ViewGroup that hosts the child Router
+     * @param tag                    The router's tag or {@code null} if none is needed
+     * @param createIfNeeded         If true, a router will be created if one does not yet exist. Else {@code null} will be returned in this case.
+     * @param boundToHostContainerId If true, a router will only ever rebind with a container with the same view id on state restoration. Note that this must be set to true if the tag is null.
+     */
+    @Nullable
+    public final Router getChildRouter(@NonNull ViewGroup container, @Nullable String tag, boolean createIfNeeded, boolean boundToHostContainerId) {
         @IdRes final int containerId = container.getId();
         if (containerId == View.NO_ID) {
             throw new IllegalStateException("You must set an id on your container.");
@@ -222,7 +238,7 @@ public abstract class Controller {
 
         ControllerHostedRouter childRouter = null;
         for (ControllerHostedRouter router : childRouters) {
-            if (router.getHostId() == containerId && TextUtils.equals(tag, router.getTag())) {
+            if (router.matches(containerId, tag)) {
                 childRouter = router;
                 break;
             }
@@ -230,7 +246,7 @@ public abstract class Controller {
 
         if (childRouter == null) {
             if (createIfNeeded) {
-                childRouter = new ControllerHostedRouter(container.getId(), tag);
+                childRouter = new ControllerHostedRouter(container.getId(), tag, boundToHostContainerId);
                 childRouter.setHostContainer(this, container);
                 childRouters.add(childRouter);
 

conductor/src/main/java/com/bluelinelabs/conductor/ControllerHostedRouter.java

@@ -5,6 +5,7 @@ import android.content.Intent;
 import android.content.IntentSender;
 import android.content.IntentSender.SendIntentException;
 import android.os.Bundle;
+import android.text.TextUtils;
 import android.view.ViewGroup;
 
 import androidx.annotation.IdRes;
@@ -22,18 +23,28 @@ class ControllerHostedRouter extends Router {
 
     private final String KEY_HOST_ID = "ControllerHostedRouter.hostId";
     private final String KEY_TAG = "ControllerHostedRouter.tag";
+    private final String KEY_BOUND_TO_CONTAINER = "ControllerHostedRouter.boundToContainer";
 
     private Controller hostController;
 
     @IdRes private int hostId;
     private String tag;
     private boolean isDetachFrozen;
+    private boolean boundToContainer;
 
     ControllerHostedRouter() { }
 
     ControllerHostedRouter(int hostId, @Nullable String tag) {
+        this(hostId, tag, false);
+    }
+
+    ControllerHostedRouter(int hostId, @Nullable String tag, boolean boundToContainer) {
+        if (!boundToContainer && tag == null) {
+            throw new IllegalStateException("ControllerHostedRouter can't be created without a tag if not bounded to its container");
+        }
         this.hostId = hostId;
         this.tag = tag;
+        this.boundToContainer = boundToContainer;
     }
 
     final void setHostController(@NonNull Controller controller) {
@@ -213,6 +224,7 @@ class ControllerHostedRouter extends Router {
         super.saveInstanceState(outState);
 
         outState.putInt(KEY_HOST_ID, hostId);
+        outState.putBoolean(KEY_BOUND_TO_CONTAINER, boundToContainer);
         outState.putString(KEY_TAG, tag);
     }
 
@@ -221,6 +233,7 @@ class ControllerHostedRouter extends Router {
         super.restoreInstanceState(savedInstanceState);
 
         hostId = savedInstanceState.getInt(KEY_HOST_ID);
+        boundToContainer = savedInstanceState.getBoolean(KEY_BOUND_TO_CONTAINER);
         tag = savedInstanceState.getString(KEY_TAG);
     }
 
@@ -234,9 +247,18 @@ class ControllerHostedRouter extends Router {
         return hostId;
     }
 
-    @Nullable
-    String getTag() {
-        return tag;
+    boolean matches(int hostId, @Nullable String tag) {
+        if (!boundToContainer && container == null) {
+            if (this.tag == null) {
+                throw new IllegalStateException("Host ID can't be variable with a null tag");
+            }
+            if (this.tag.equals(tag)) {
+                this.hostId = hostId;
+                return true;
+            }
+        }
+
+        return this.hostId == hostId && TextUtils.equals(tag, this.tag);
     }
 
     @Override @NonNull