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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Native Modules · React Native</title><meta name="viewport" content="width=device-width"/><meta name="generator" content="Docusaurus"/><meta property="og:title" content="Native Modules · React Native"/><meta property="og:type" content="website"/><meta property="og:url" content="https://facebook.github.io/react-native/index.html"/><meta property="og:description" content="Sometimes an app needs access to a platform API that React Native doesn&#x27;t have a corresponding module for yet. Maybe you want to reuse some existing Java code without having to reimplement it in JavaScript, or write some high performance, multi-threaded code such as for image processing, a database, or any number of advanced extensions."/><meta name="twitter:card" content="summary"/><link rel="shortcut icon" href="/react-native/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/solarized-dark.min.css"/><link rel="alternate" type="application/atom+xml" href="https://facebook.github.io/blog/atom.xml" title="React Native Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://facebook.github.io/blog/feed.xml" title="React Native Blog RSS Feed"/><script>
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<p>We designed React Native such that it is possible for you to write real native code and have access to the full power of the platform. This is a more advanced feature and we don't expect it to be part of the usual development process, however it is essential that it exists. If React Native doesn't support a native feature that you need, you should be able to build it yourself.</p>
<h3><a class="anchor" aria-hidden="true" id="enable-gradle"></a><a href="#enable-gradle" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Enable Gradle</h3>
<p>If you plan to make changes in Java code, we recommend enabling <a href="https://docs.gradle.org/2.9/userguide/gradle_daemon.html">Gradle Daemon</a> to speed up builds.</p>
<h2><a class="anchor" aria-hidden="true" id="the-toast-module"></a><a href="#the-toast-module" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>The Toast Module</h2>
<p>This guide will use the <a href="http://developer.android.com/reference/android/widget/Toast.html">Toast</a> example. Let's say we would like to be able to create a toast message from JavaScript.</p>
<p>We start by creating a native module. A native module is a Java class that usually extends the <code>ReactContextBaseJavaModule</code> class and implements the functionality required by the JavaScript. Our goal here is to be able to write <code>ToastExample.show('Awesome', ToastExample.SHORT);</code> from JavaScript to display a short toast on the screen.</p>
<pre><code class="hljs css java"><span class="hljs-keyword">package</span> com.facebook.react.modules.toast;
<pre><code class="hljs css languages- java"><span class="hljs-keyword">package</span> com.facebook.react.modules.toast;
<span class="hljs-keyword">import</span> android.widget.Toast;
@@ -43,13 +60,13 @@
}
</code></pre>
<p><code>ReactContextBaseJavaModule</code> requires that a method called <code>getName</code> is implemented. The purpose of this method is to return the string name of the <code>NativeModule</code> which represents this class in JavaScript. So here we will call this <code>ToastExample</code> so that we can access it through <code>React.NativeModules.ToastExample</code> in JavaScript.</p>
<pre><code class="hljs css java"> <span class="hljs-meta">@Override</span>
<pre><code class="hljs css languages- java"> <span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">getName</span><span class="hljs-params">()</span> </span>{
<span class="hljs-keyword">return</span> <span class="hljs-string">"ToastExample"</span>;
}
</code></pre>
<p>An optional method called <code>getConstants</code> returns the constant values exposed to JavaScript. Its implementation is not required but is very useful to key pre-defined values that need to be communicated from JavaScript to Java in sync.</p>
<pre><code class="hljs css java"> <span class="hljs-meta">@Override</span>
<pre><code class="hljs css languages- java"> <span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> Map&lt;String, Object&gt; <span class="hljs-title">getConstants</span><span class="hljs-params">()</span> </span>{
<span class="hljs-keyword">final</span> Map&lt;String, Object&gt; constants = <span class="hljs-keyword">new</span> HashMap&lt;&gt;();
constants.put(DURATION_SHORT_KEY, Toast.LENGTH_SHORT);
@@ -58,7 +75,7 @@
}
</code></pre>
<p>To expose a method to JavaScript a Java method must be annotated using <code>@ReactMethod</code>. The return type of bridge methods is always <code>void</code>. React Native bridge is asynchronous, so the only way to pass a result to JavaScript is by using callbacks or emitting events (see below).</p>
<pre><code class="hljs css java"> <span class="hljs-meta">@ReactMethod</span>
<pre><code class="hljs css languages- java"> <span class="hljs-meta">@ReactMethod</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">show</span><span class="hljs-params">(String message, <span class="hljs-keyword">int</span> duration)</span> </span>{
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
@@ -77,7 +94,7 @@ R<span class="hljs-function"><span class="hljs-title">eadableArray</span> -&gt;<
<p>Read more about <a href="https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReadableMap.java">ReadableMap</a> and <a href="https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReadableArray.java">ReadableArray</a></p>
<h3><a class="anchor" aria-hidden="true" id="register-the-module"></a><a href="#register-the-module" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Register the Module</h3>
<p>The last step within Java is to register the Module; this happens in the <code>createNativeModules</code> of your apps package. If a module is not registered it will not be available from JavaScript.</p>
<pre><code class="hljs css java"><span class="hljs-keyword">package</span> com.facebook.react.modules.toast;
<pre><code class="hljs css languages- java"><span class="hljs-keyword">package</span> com.facebook.react.modules.toast;
<span class="hljs-keyword">import</span> com.facebook.react.ReactPackage;
<span class="hljs-keyword">import</span> com.facebook.react.bridge.NativeModule;
@@ -108,14 +125,14 @@ R<span class="hljs-function"><span class="hljs-title">eadableArray</span> -&gt;<
}
</code></pre>
<p>The package needs to be provided in the <code>getPackages</code> method of the <code>MainApplication.java</code> file. This file exists under the android folder in your react-native application directory. The path to this file is: <code>android/app/src/main/java/com/your-app-name/MainApplication.java</code>.</p>
<pre><code class="hljs css java"><span class="hljs-function"><span class="hljs-keyword">protected</span> List&lt;ReactPackage&gt; <span class="hljs-title">getPackages</span><span class="hljs-params">()</span> </span>{
<pre><code class="hljs css languages- java"><span class="hljs-function"><span class="hljs-keyword">protected</span> List&lt;ReactPackage&gt; <span class="hljs-title">getPackages</span><span class="hljs-params">()</span> </span>{
<span class="hljs-keyword">return</span> Arrays.&lt;ReactPackage&gt;asList(
<span class="hljs-keyword">new</span> MainReactPackage(),
<span class="hljs-keyword">new</span> AnExampleReactPackage()); <span class="hljs-comment">// &lt;-- Add this line with your package name.</span>
}
</code></pre>
<p>To make it simpler to access your new functionality from JavaScript, it is common to wrap the native module in a JavaScript module. This is not necessary but saves the consumers of your library the need to pull it off of <code>NativeModules</code> each time. This JavaScript file also becomes a good location for you to add any JavaScript side functionality.</p>
<pre><code class="hljs css javascript"><span class="hljs-comment">/**
<pre><code class="hljs css languages- javascript"><span class="hljs-comment">/**
* This exposes the native ToastExample module as a JS module. This has a
* function 'show' which takes the following parameters:
*
@@ -127,14 +144,14 @@ R<span class="hljs-function"><span class="hljs-title">eadableArray</span> -&gt;<
<span class="hljs-built_in">module</span>.exports = NativeModules.ToastExample;
</code></pre>
<p>Now, from your other JavaScript file you can call the method like this:</p>
<pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> ToastExample <span class="hljs-keyword">from</span> <span class="hljs-string">'./ToastExample'</span>;
<pre><code class="hljs css languages- javascript"><span class="hljs-keyword">import</span> ToastExample <span class="hljs-keyword">from</span> <span class="hljs-string">'./ToastExample'</span>;
ToastExample.show(<span class="hljs-string">'Awesome'</span>, ToastExample.SHORT);
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="beyond-toasts"></a><a href="#beyond-toasts" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Beyond Toasts</h2>
<h3><a class="anchor" aria-hidden="true" id="callbacks"></a><a href="#callbacks" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Callbacks</h3>
<p>Native modules also support a special kind of argument - a callback. In most cases it is used to provide the function call result to JavaScript.</p>
<pre><code class="hljs css java"><span class="hljs-keyword">import</span> com.facebook.react.bridge.Callback;
<pre><code class="hljs css languages- java"><span class="hljs-keyword">import</span> com.facebook.react.bridge.Callback;
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">UIManagerModule</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">ReactContextBaseJavaModule</span> </span>{
@@ -161,7 +178,7 @@ ToastExample.show(<span class="hljs-string">'Awesome'</span>, ToastExample.SHORT
...
</code></pre>
<p>This method would be accessed in JavaScript using:</p>
<pre><code class="hljs css javascript">UIManager.measureLayout(
<pre><code class="hljs css languages- javascript">UIManager.measureLayout(
<span class="hljs-number">100</span>,
<span class="hljs-number">100</span>,
(msg) =&gt; {
@@ -177,7 +194,7 @@ ToastExample.show(<span class="hljs-string">'Awesome'</span>, ToastExample.SHORT
<h3><a class="anchor" aria-hidden="true" id="promises"></a><a href="#promises" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Promises</h3>
<p>Native modules can also fulfill a promise, which can simplify your code, especially when using ES2016's <code>async/await</code> syntax. When the last parameter of a bridged native method is a <code>Promise</code>, its corresponding JS method will return a JS Promise object.</p>
<p>Refactoring the above code to use a promise instead of callbacks looks like this:</p>
<pre><code class="hljs css java"><span class="hljs-keyword">import</span> com.facebook.react.bridge.Promise;
<pre><code class="hljs css languages- java"><span class="hljs-keyword">import</span> com.facebook.react.bridge.Promise;
<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">UIManagerModule</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">ReactContextBaseJavaModule</span> </span>{
@@ -207,7 +224,7 @@ ToastExample.show(<span class="hljs-string">'Awesome'</span>, ToastExample.SHORT
...
</code></pre>
<p>The JavaScript counterpart of this method returns a Promise. This means you can use the <code>await</code> keyword within an async function to call it and wait for its result:</p>
<pre><code class="hljs css javascript"><span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">measureLayout</span>(<span class="hljs-params"></span>) </span>{
<pre><code class="hljs css languages- javascript"><span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">measureLayout</span>(<span class="hljs-params"></span>) </span>{
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">var</span> {relativeX, relativeY, width, height} = <span class="hljs-keyword">await</span> UIManager.measureLayout(
<span class="hljs-number">100</span>,
@@ -226,7 +243,7 @@ measureLayout();
<p>Native modules should not have any assumptions about what thread they are being called on, as the current assignment is subject to change in the future. If a blocking call is required, the heavy work should be dispatched to an internally managed worker thread, and any callbacks distributed from there.</p>
<h3><a class="anchor" aria-hidden="true" id="sending-events-to-javascript"></a><a href="#sending-events-to-javascript" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Sending Events to JavaScript</h3>
<p>Native modules can signal events to JavaScript without being invoked directly. The easiest way to do this is to use the <code>RCTDeviceEventEmitter</code> which can be obtained from the <code>ReactContext</code> as in the code snippet below.</p>
<pre><code class="hljs css java">...
<pre><code class="hljs css languages- java">...
<span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">void</span> <span class="hljs-title">sendEvent</span><span class="hljs-params">(ReactContext reactContext,
String eventName,
@Nullable WritableMap params)</span> </span>{
@@ -240,7 +257,7 @@ WritableMap params = Arguments.createMap();
sendEvent(reactContext, <span class="hljs-string">"keyboardWillShow"</span>, params);
</code></pre>
<p>JavaScript modules can then register to receive events by <code>addListenerOn</code> using the <code>Subscribable</code> mixin.</p>
<pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> { DeviceEventEmitter } <span class="hljs-keyword">from</span> <span class="hljs-string">'react-native'</span>;
<pre><code class="hljs css languages- javascript"><span class="hljs-keyword">import</span> { DeviceEventEmitter } <span class="hljs-keyword">from</span> <span class="hljs-string">'react-native'</span>;
...
var ScrollResponderMixin = {
@@ -260,7 +277,7 @@ var ScrollResponderMixin = {
},
</code></pre>
<p>You can also directly use the <code>DeviceEventEmitter</code> module to listen for events.</p>
<pre><code class="hljs css javascript">...
<pre><code class="hljs css languages- javascript">...
componentWillMount: <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params"></span>) </span>{
DeviceEventEmitter.addListener(<span class="hljs-string">'keyboardWillShow'</span>, <span class="hljs-function"><span class="hljs-keyword">function</span>(<span class="hljs-params">e: Event</span>) </span>{
<span class="hljs-comment">// handle event.</span>
@@ -270,10 +287,10 @@ componentWillMount: <span class="hljs-function"><span class="hljs-keyword">funct
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="getting-activity-result-from-startactivityforresult"></a><a href="#getting-activity-result-from-startactivityforresult" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Getting activity result from <code>startActivityForResult</code></h3>
<p>You'll need to listen to <code>onActivityResult</code> if you want to get results from an activity you started with <code>startActivityForResult</code>. To do this, you must extend <code>BaseActivityEventListener</code> or implement <code>ActivityEventListener</code>. The former is preferred as it is more resilient to API changes. Then, you need to register the listener in the module's constructor,</p>
<pre><code class="hljs css java">reactContext.addActivityEventListener(mActivityResultListener);
<pre><code class="hljs css languages- java">reactContext.addActivityEventListener(mActivityResultListener);
</code></pre>
<p>Now you can listen to <code>onActivityResult</code> by implementing the following method:</p>
<pre><code class="hljs css java"><span class="hljs-meta">@Override</span>
<pre><code class="hljs css languages- java"><span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onActivityResult</span><span class="hljs-params">(
<span class="hljs-keyword">final</span> Activity activity,
<span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> requestCode,
@@ -283,7 +300,7 @@ componentWillMount: <span class="hljs-function"><span class="hljs-keyword">funct
}
</code></pre>
<p>We will implement a simple image picker to demonstrate this. The image picker will expose the method <code>pickImage</code> to JavaScript, which will return the path of the image when called.</p>
<pre><code class="hljs css java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">ImagePickerModule</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">ReactContextBaseJavaModule</span> </span>{
<pre><code class="hljs css languages- java"><span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">ImagePickerModule</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">ReactContextBaseJavaModule</span> </span>{
<span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> IMAGE_PICKER_REQUEST = <span class="hljs-number">467081</span>;
<span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String E_ACTIVITY_DOES_NOT_EXIST = <span class="hljs-string">"E_ACTIVITY_DOES_NOT_EXIST"</span>;
@@ -358,10 +375,10 @@ componentWillMount: <span class="hljs-function"><span class="hljs-keyword">funct
</code></pre>
<h3><a class="anchor" aria-hidden="true" id="listening-to-lifecycle-events"></a><a href="#listening-to-lifecycle-events" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Listening to LifeCycle events</h3>
<p>Listening to the activity's LifeCycle events such as <code>onResume</code>, <code>onPause</code> etc. is very similar to how we implemented <code>ActivityEventListener</code>. The module must implement <code>LifecycleEventListener</code>. Then, you need to register a listener in the module's constructor,</p>
<pre><code class="hljs css java">reactContext.addLifecycleEventListener(<span class="hljs-keyword">this</span>);
<pre><code class="hljs css languages- java">reactContext.addLifecycleEventListener(<span class="hljs-keyword">this</span>);
</code></pre>
<p>Now you can listen to the activity's LifeCycle events by implementing the following methods:</p>
<pre><code class="hljs css java"><span class="hljs-meta">@Override</span>
<pre><code class="hljs css languages- java"><span class="hljs-meta">@Override</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">onHostResume</span><span class="hljs-params">()</span> </span>{
<span class="hljs-comment">// Activity `onResume`</span>
}
@@ -376,7 +393,7 @@ componentWillMount: <span class="hljs-function"><span class="hljs-keyword">funct
<span class="hljs-comment">// Activity `onDestroy`</span>
}
</code></pre>
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