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<!DOCTYPE html><html><head><title>Native Modules</title><meta charset="utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta name="viewport" content="width=device-width"><meta property="fb:app_id" content="1677033832619985"><meta property="fb:admins" content="121800083"><meta property="og:site_name" content="React Native"><meta property="og:title" content="Native Modules"><meta property="og:url" content="https://facebook.github.io/react-native/index.html"><meta property="og:image" content="https://facebook.github.io/react-native/img/opengraph.png"><meta property="og:description" content="A framework for building native apps using React"><meta name="twitter:site" content="@reactnative"><meta name="twitter:card" content="summary_large_image"><meta property="og:type" content="website"><base href="/react-native/"><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"><link rel="shortcut icon" href="img/favicon.png?2"><link rel="stylesheet" href="css/react-native.css"><link rel="alternate" type="application/rss+xml" title="React Native Blog" href="https://facebook.github.io/react-native/blog/feed.xml"><link href="//cdn-images.mailchimp.com/embedcode/horizontal-slim-10_7.css" rel="stylesheet" type="text/css"><script type="text/javascript" src="//use.typekit.net/vqa1hcx.js"></script><script type="text/javascript">try{Typekit.load();}catch(e){}</script></head><body><script>window.fbAsyncInit = function() {FB.init({appId:'1677033832619985',xfbml:true,version:'v2.7'});};(function(d, s, id){var js, fjs = d.getElementsByTagName(s)[0];if (d.getElementById(id)) {return;}js = d.createElement(s); js.id = id;js.src = '//connect.facebook.net/en_US/sdk.js';fjs.parentNode.insertBefore(js, fjs);}(document, 'script','facebook-jssdk'));</script><script>window.twttr=(function(d,s, id){var js,fjs=d.getElementsByTagName(s)[0],t=window.twttr||{};if(d.getElementById(id))return t;js=d.createElement(s);js.id=id;js.src='https://platform.twitter.com/widgets.js';fjs.parentNode.insertBefore(js, fjs);t._e = [];t.ready = function(f) {t._e.push(f);};return t;}(document, 'script', 'twitter-wjs'));</script><div class="container"><div class="nav-main"><div class="wrap"><a class="nav-home" href=""><img src="img/header_logo.png">React Native</a><a class="nav-version" href="/react-native/versions.html">0.45</a><div class="nav-site-wrapper"><ul class="nav-site nav-site-internal"><li><a href="docs/getting-started.html" class="active" data-target=".nav-docs">Docs</a></li><li><a href="/react-native/support.html" class="">Help</a></li><li><a href="/react-native/showcase.html" class="">Showcase</a></li><li><a href="/react-native/blog/" class="">Blog</a></li></ul><div class="algolia-search-wrapper"><input id="algolia-doc-search" tabindex="0" type="text" placeholder="Search docs..."></div><ul class="nav-site nav-site-external"><li><a href="https://github.com/facebook/react-native" class="">GitHub</a></li><li><a href="http://facebook.github.io/react" class="">React</a></li></ul></div></div></div><section class="content wrap documentationContent"><div class="nav-docs"><div class="nav-docs-viewport"><div class="nav-docs-section"><h3>The Basics</h3><ul><li><a style="margin-left:10px;" class="" href="docs/getting-started.html">Getting Started</a></li><li><a style="margin-left:10px;" class="" href="docs/tutorial.html">Tutorial</a></li><li><a style="margin-left:10px;" class="" href="docs/props.html">Props</a></li><li><a style="margin-left:10px;" class="" href="docs/state.html">State</a></li><li><a style="margin-left:10px;" class="" href="docs/style.html">Style</a></li><li><a style="margin-left:10px;" class="" href="docs/height-and-width.html">Height and Width</a></li><li><a style="margin-left:10px;" class="" href="docs/flexbox.html">Layout with Flexbox</a></li><li><a style="margin-left:10px;" class="" href="docs/handling-text-input.html">Handling Text Input</a></li><li><a style="margin-left:10px;" class="" href="docs/using-a-scrollview.html">Using a ScrollView</a></li><li><a style="margin-left:10px;" class="" href="docs/using-a-listview.html">Using List Views</a></li><li><a style="margin-left:10px;" class="" href="docs/network.html">Networking</a></li><li><a style="margin-left:10px;" class="" href="docs/more-resources.html">More Resources</a></li></ul></div><div class="nav-docs-section"><h3>Guides</h3><ul><li><a style="margin-left:10px;" class="" href="docs/handling-touches.html">Handling Touches</a></li><li><a style="margin-left:10px;" class="" href="docs/animations.html">Animations</a></li><li><a style="margin-left:10px;" class="" href="docs/navigation.html">Navigation</a></li><li><a style="margin-left:10px;" class="" href="docs/images.html">Images</a></li><li><a style="margin-left:10px;" class="" href="docs/colors.html">Colors</a></li><li><a style="margin-left:10px;" class="" href="docs/platform-specific-code.html">Platform Specific Code</a></li><li><a style="margin-left:10px;" class="" href="docs/debugging.html">Debugging</a></li><li><a style="margin-left:10px;" class="" href="docs/accessibility.html">Accessibility</a></li><li><a style="margin-left:10px;" class="" href="docs/timers.html">Timers</a></li><li><a style="margin-left:10px;" class="" href="docs/javascript-environment.html">JavaScript Environment</a></li><li><a style="margin-left:10px;" class="" href="docs/direct-manipulation.html">Direct Manipulation</a></li><li><a style="margin-left:10px;" class="" href="docs/performance.html">Performance</a></li><li><a style="margin-left:10px;" class="" href="docs/gesture-responder-system.html">Gesture Responder System</a></li><li><a style="margin-left:10px;" class="" href="docs/testing.html">Testing</a></li><li><a style="margin-left:10px;" class="" href="docs/understanding-cli.html">Understanding the CLI</a></li><li><a style="margin-left:10px;" class="" href="docs/integration-with-existing-apps.html">Integration With Existing Apps</a></li><li><a style="margin-left:10px;" class="" href="docs/running-on-device.html">Running On Device</a></li><li><a style="margin-left:10px;" class="" href="docs/upgrading.html">Upgrading to new React Native versions</a></li></ul></div><div class="nav-docs-section"><h3>Guides (iOS)</h3><ul><li><a style="margin-left:10px;" class="" href="docs/native-modules-ios.html">Native Modules</a></li><li><a style="margin-left:10px;" class="" href="docs/native-components-ios.html">Native UI Components</a></li><li><a style="margin-left:10px;" class="" href="docs/linking-libraries-ios.html">Linking Libraries</a></li><li><a style="margin-left:10px;" class="" href="docs/running-on-simulator-ios.html">Running On Simulator</a></li><li><a style="margin-left:10px;" class="" href="docs/communication-ios.html">Communication between native and React Native</a></li></ul></div><div class="nav-docs-section"><h3>Guides (Apple TV)</h3><ul><li><a style="margin-left:10px;" class="" href="docs/building-for-apple-tv.html">Building For Apple TV</a></li></ul></div><div class="nav-docs-section"><h3>Guides (Android)</h3><ul><li><a style="margin-left:10px;" class="active" href="docs/native-modules-android.html">Native Modules</a></li><li><a style="margin-left:10px;" class="" href="docs/native-components-android.html">Native UI Components</a></li><li><a style="margin-left:10px;" class="" href="docs/headless-js-android.html">Headless JS</a></li><li><a style="margin-left:10px;" class="" href="docs/signed-apk-android.html">Generating Signed APK</a></li><li><a style="margin-left:10px;" class="" href="docs/android-building-from-source.html">Building React Native from source</a></li></ul></div><div class="nav-docs-section"><h3>components</h3><ul><li><a style="margin-left:10px;" class="" href="docs/activityindicator.html">ActivityIndicator</a></li><li><a style="margin-left:10px;" class="" href="docs/button.html">Button</a></li><li><a style="margin-left:10px;" class="" href="docs/datepickerios.html">DatePickerIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/drawerlayoutandroid.html">DrawerLayoutAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/flatlist.html">FlatList</a></li><li><a style="margin-left:10px;" class="" href="docs/image.html">Image</a></li><li><a style="margin-left:10px;" class="" href="docs/keyboardavoidingview.html">KeyboardAvoidingView</a></li><li><a style="margin-left:10px;" class="" href="docs/listview.html">ListView</a></li><li><a style="margin-left:10px;" class="" href="docs/modal.html">Modal</a></li><li><a style="margin-left:10px;" class="" href="docs/navigatorios.html">NavigatorIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/picker.html">Picker</a></li><li><a style="margin-left:10px;" class="" href="docs/pickerios.html">PickerIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/progressbarandroid.html">ProgressBarAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/progressviewios.html">ProgressViewIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/refreshcontrol.html">RefreshControl</a></li><li><a style="margin-left:10px;" class="" href="docs/scrollview.html">ScrollView</a></li><li><a style="margin-left:10px;" class="" href="docs/sectionlist.html">SectionList</a></li><li><a style="margin-left:10px;" class="" href="docs/segmentedcontrolios.html">SegmentedControlIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/slider.html">Slider</a></li><li><a style="margin-left:10px;" class="" href="docs/snapshotviewios.html">SnapshotViewIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/statusbar.html">StatusBar</a></li><li><a style="margin-left:10px;" class="" href="docs/switch.html">Switch</a></li><li><a style="margin-left:10px;" class="" href="docs/tabbarios.html">TabBarIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/tabbarios-item.html">TabBarIOS.Item</a></li><li><a style="margin-left:10px;" class="" href="docs/text.html">Text</a></li><li><a style="margin-left:10px;" class="" href="docs/textinput.html">TextInput</a></li><li><a style="margin-left:10px;" class="" href="docs/toolbarandroid.html">ToolbarAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/touchablehighlight.html">TouchableHighlight</a></li><li><a style="margin-left:10px;" class="" href="docs/touchablenativefeedback.html">TouchableNativeFeedback</a></li><li><a style="margin-left:10px;" class="" href="docs/touchableopacity.html">TouchableOpacity</a></li><li><a style="margin-left:10px;" class="" href="docs/touchablewithoutfeedback.html">TouchableWithoutFeedback</a></li><li><a style="margin-left:10px;" class="" href="docs/view.html">View</a></li><li><a style="margin-left:10px;" class="" href="docs/viewpagerandroid.html">ViewPagerAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/virtualizedlist.html">VirtualizedList</a></li><li><a style="margin-left:10px;" class="" href="docs/webview.html">WebView</a></li></ul></div><div class="nav-docs-section"><h3>APIs</h3><ul><li><a style="margin-left:10px;" class="" href="docs/accessibilityinfo.html">AccessibilityInfo</a></li><li><a style="margin-left:10px;" class="" href="docs/actionsheetios.html">ActionSheetIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/adsupportios.html">AdSupportIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/alert.html">Alert</a></li><li><a style="margin-left:10px;" class="" href="docs/alertios.html">AlertIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/animated.html">Animated</a></li><li><a style="margin-left:10px;" class="" href="docs/appregistry.html">AppRegistry</a></li><li><a style="margin-left:10px;" class="" href="docs/appstate.html">AppState</a></li><li><a style="margin-left:10px;" class="" href="docs/asyncstorage.html">AsyncStorage</a></li><li><a style="margin-left:10px;" class="" href="docs/backandroid.html">BackAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/backhandler.html">BackHandler</a></li><li><a style="margin-left:10px;" class="" href="docs/cameraroll.html">CameraRoll</a></li><li><a style="margin-left:10px;" class="" href="docs/clipboard.html">Clipboard</a></li><li><a style="margin-left:10px;" class="" href="docs/datepickerandroid.html">DatePickerAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/dimensions.html">Dimensions</a></li><li><a style="margin-left:10px;" class="" href="docs/easing.html">Easing</a></li><li><a style="margin-left:10px;" class="" href="docs/geolocation.html">Geolocation</a></li><li><a style="margin-left:10px;" class="" href="docs/imageeditor.html">ImageEditor</a></li><li><a style="margin-left:10px;" class="" href="docs/imagepickerios.html">ImagePickerIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/imagestore.html">ImageStore</a></li><li><a style="margin-left:10px;" class="" href="docs/interactionmanager.html">InteractionManager</a></li><li><a style="margin-left:10px;" class="" href="docs/keyboard.html">Keyboard</a></li><li><a style="margin-left:10px;" class="" href="docs/layoutanimation.html">LayoutAnimation</a></li><li><a style="margin-left:10px;" class="" href="docs/linking.html">Linking</a></li><li><a style="margin-left:10px;" class="" href="docs/nativemethodsmixin.html">NativeMethodsMixin</a></li><li><a style="margin-left:10px;" class="" href="docs/netinfo.html">NetInfo</a></li><li><a style="margin-left:10px;" class="" href="docs/panresponder.html">PanResponder</a></li><li><a style="margin-left:10px;" class="" href="docs/permissionsandroid.html">PermissionsAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/pixelratio.html">PixelRatio</a></li><li><a style="margin-left:10px;" class="" href="docs/pushnotificationios.html">PushNotificationIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/settings.html">Settings</a></li><li><a style="margin-left:10px;" class="" href="docs/share.html">Share</a></li><li><a style="margin-left:10px;" class="" href="docs/statusbarios.html">StatusBarIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/stylesheet.html">StyleSheet</a></li><li><a style="margin-left:10px;" class="" href="docs/systrace.html">Systrace</a></li><li><a style="margin-left:10px;" class="" href="docs/timepickerandroid.html">TimePickerAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/toastandroid.html">ToastAndroid</a></li><li><a style="margin-left:10px;" class="" href="docs/vibration.html">Vibration</a></li><li><a style="margin-left:10px;" class="" href="docs/vibrationios.html">VibrationIOS</a></li><li><a style="margin-left:10px;" class="" href="docs/layout-props.html">Layout Props</a></li><li><a style="margin-left:10px;" class="" href="docs/shadow-props.html">Shadow Props</a></li></ul></div></div></div><div class="inner-content"><a id="content"></a><h1><a class="anchor" name="native-modules"></a>Native Modules <a class="hash-link" href="docs/native-modules-android.html#native-modules">#</a></h1><div class="banner-crna-ejected"><h3>Project with Native Code Required</h3><p>This page only applies to projects made with <code>react-native init</code> or to those made with Create React Native App which have since ejected. For more information about ejecting, please see the <a href="https://github.com/react-community/create-react-native-app/blob/master/EJECTING.md" target="_blank">guide</a> on the Create React Native App repository.</p></div><div><p>Sometimes an app needs access to a platform API that React Native doesn'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.</p><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" name="enable-gradle"></a>Enable Gradle <a class="hash-link" href="docs/native-modules-android.html#enable-gradle">#</a></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" target="_blank">Gradle Daemon</a> to speed up builds.</p><h2><a class="anchor" name="the-toast-module"></a>The Toast Module <a class="hash-link" href="docs/native-modules-android.html#the-toast-module">#</a></h2><p>This guide will use the <a href="http://developer.android.com/reference/android/widget/Toast.html" target="_blank">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>ToastAndroid.show('Awesome', ToastAndroid.SHORT);</code> from JavaScript to display a short toast on the screen.</p><div class="prism language-javascript">package com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>modules<span class="token punctuation">.</span>toast<span class="token punctuation">;</span>
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import android<span class="token punctuation">.</span>widget<span class="token punctuation">.</span>Toast<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>NativeModule<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>ReactApplicationContext<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>ReactContext<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>ReactContextBaseJavaModule<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>ReactMethod<span class="token punctuation">;</span>
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import java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>Map<span class="token punctuation">;</span>
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public class <span class="token class-name">ToastModule</span> extends <span class="token class-name">ReactContextBaseJavaModule</span> <span class="token punctuation">{</span>
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private static final String DURATION_SHORT_KEY <span class="token operator">=</span> <span class="token string">"SHORT"</span><span class="token punctuation">;</span>
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private static final String DURATION_LONG_KEY <span class="token operator">=</span> <span class="token string">"LONG"</span><span class="token punctuation">;</span>
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public <span class="token function">ToastModule<span class="token punctuation">(</span></span>ReactApplicationContext reactContext<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token function">super<span class="token punctuation">(</span></span>reactContext<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span></div><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>ToastAndroid</code> so that we can access it through <code>React.NativeModules.ToastAndroid</code> in JavaScript.</p><div class="prism language-javascript"> @Override
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public String <span class="token function">getName<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">return</span> <span class="token string">"ToastAndroid"</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span></div><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><div class="prism language-javascript"> @Override
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public Map<String<span class="token punctuation">,</span> Object<span class="token operator">></span> <span class="token function">getConstants<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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final Map<String<span class="token punctuation">,</span> Object<span class="token operator">></span> constants <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HashMap</span><<span class="token operator">></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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constants<span class="token punctuation">.</span><span class="token function">put<span class="token punctuation">(</span></span>DURATION_SHORT_KEY<span class="token punctuation">,</span> Toast<span class="token punctuation">.</span>LENGTH_SHORT<span class="token punctuation">)</span><span class="token punctuation">;</span>
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constants<span class="token punctuation">.</span><span class="token function">put<span class="token punctuation">(</span></span>DURATION_LONG_KEY<span class="token punctuation">,</span> Toast<span class="token punctuation">.</span>LENGTH_LONG<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> constants<span class="token punctuation">;</span>
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<span class="token punctuation">}</span></div><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><div class="prism language-javascript"> @ReactMethod
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public void <span class="token function">show<span class="token punctuation">(</span></span>String message<span class="token punctuation">,</span> int duration<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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Toast<span class="token punctuation">.</span><span class="token function">makeText<span class="token punctuation">(</span></span><span class="token function">getReactApplicationContext<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">,</span> message<span class="token punctuation">,</span> duration<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">show<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span></div><h3><a class="anchor" name="argument-types"></a>Argument Types <a class="hash-link" href="docs/native-modules-android.html#argument-types">#</a></h3><p>The following argument types are supported for methods annotated with <code>@ReactMethod</code> and they directly map to their JavaScript equivalents</p><div class="prism language-javascript">Boolean <span class="token operator">-</span><span class="token operator">></span> Bool
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Integer <span class="token operator">-</span><span class="token operator">></span> Number
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Double <span class="token operator">-</span><span class="token operator">></span> Number
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Float <span class="token operator">-</span><span class="token operator">></span> Number
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String <span class="token operator">-</span><span class="token operator">></span> String
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Callback <span class="token operator">-</span><span class="token operator">></span> <span class="token keyword">function</span>
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ReadableMap <span class="token operator">-</span><span class="token operator">></span> Object
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ReadableArray <span class="token operator">-</span><span class="token operator">></span> Array</div><p>Read more about <a href="https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReadableMap.java" target="_blank">ReadableMap</a> and <a href="https://github.com/facebook/react-native/blob/master/ReactAndroid/src/main/java/com/facebook/react/bridge/ReadableArray.java" target="_blank">ReadableArray</a></p><h3><a class="anchor" name="register-the-module"></a>Register the Module <a class="hash-link" href="docs/native-modules-android.html#register-the-module">#</a></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><div class="prism language-javascript">package com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>modules<span class="token punctuation">.</span>toast<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>ReactPackage<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>JavaScriptModule<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>NativeModule<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>ReactApplicationContext<span class="token punctuation">;</span>
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import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>uimanager<span class="token punctuation">.</span>ViewManager<span class="token punctuation">;</span>
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import java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>ArrayList<span class="token punctuation">;</span>
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import java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>Collections<span class="token punctuation">;</span>
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import java<span class="token punctuation">.</span>util<span class="token punctuation">.</span>List<span class="token punctuation">;</span>
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public class <span class="token class-name">AnExampleReactPackage</span> implements <span class="token class-name">ReactPackage</span> <span class="token punctuation">{</span>
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@Override
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public List<Class<<span class="token operator">?</span> extends <span class="token class-name">JavaScriptModule</span><span class="token operator">></span><span class="token operator">></span> <span class="token function">createJSModules<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">return</span> Collections<span class="token punctuation">.</span><span class="token function">emptyList<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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@Override
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public List<ViewManager<span class="token operator">></span> <span class="token function">createViewManagers<span class="token punctuation">(</span></span>ReactApplicationContext reactContext<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">return</span> Collections<span class="token punctuation">.</span><span class="token function">emptyList<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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@Override
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public List<NativeModule<span class="token operator">></span> <span class="token function">createNativeModules<span class="token punctuation">(</span></span>
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ReactApplicationContext reactContext<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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List<NativeModule<span class="token operator">></span> modules <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><<span class="token operator">></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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modules<span class="token punctuation">.</span><span class="token function">add<span class="token punctuation">(</span></span><span class="token keyword">new</span> <span class="token class-name">ToastModule</span><span class="token punctuation">(</span>reactContext<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span> modules<span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span></div><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><div class="prism language-javascript">protected List<ReactPackage<span class="token operator">></span> <span class="token function">getPackages<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">return</span> Arrays<span class="token punctuation">.</span><ReactPackage<span class="token operator">></span><span class="token function">asList<span class="token punctuation">(</span></span>
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<span class="token keyword">new</span> <span class="token class-name">MainReactPackage</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
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<span class="token keyword">new</span> <span class="token class-name">AnExampleReactPackage</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment" spellcheck="true"> // <-- Add this line with your package name.
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</span><span class="token punctuation">}</span></div><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><div class="prism language-javascript"><span class="token string">'use strict'</span><span class="token punctuation">;</span>
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<span class="token comment" spellcheck="true">/**
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* This exposes the native ToastAndroid module as a JS module. This has a
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* function 'show' which takes the following parameters:
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*
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* 1. String message: A string with the text to toast
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* 2. int duration: The duration of the toast. May be ToastAndroid.SHORT or
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* ToastAndroid.LONG
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*/</span>
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import <span class="token punctuation">{</span> NativeModules <span class="token punctuation">}</span> from <span class="token string">'react-native'</span><span class="token punctuation">;</span>
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module<span class="token punctuation">.</span>exports <span class="token operator">=</span> NativeModules<span class="token punctuation">.</span>ToastAndroid<span class="token punctuation">;</span></div><p>Now, from your other JavaScript file you can call the method like this:</p><div class="prism language-javascript">import ToastAndroid from <span class="token string">'./ToastAndroid'</span><span class="token punctuation">;</span>
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ToastAndroid<span class="token punctuation">.</span><span class="token function">show<span class="token punctuation">(</span></span><span class="token string">'Awesome'</span><span class="token punctuation">,</span> ToastAndroid<span class="token punctuation">.</span>SHORT<span class="token punctuation">)</span><span class="token punctuation">;</span></div><h2><a class="anchor" name="beyond-toasts"></a>Beyond Toasts <a class="hash-link" href="docs/native-modules-android.html#beyond-toasts">#</a></h2><h3><a class="anchor" name="callbacks"></a>Callbacks <a class="hash-link" href="docs/native-modules-android.html#callbacks">#</a></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><div class="prism language-javascript">public class <span class="token class-name">UIManagerModule</span> extends <span class="token class-name">ReactContextBaseJavaModule</span> <span class="token punctuation">{</span>
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<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
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@ReactMethod
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public void <span class="token function">measureLayout<span class="token punctuation">(</span></span>
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int tag<span class="token punctuation">,</span>
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int ancestorTag<span class="token punctuation">,</span>
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Callback errorCallback<span class="token punctuation">,</span>
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Callback successCallback<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span>
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<span class="token function">measureLayout<span class="token punctuation">(</span></span>tag<span class="token punctuation">,</span> ancestorTag<span class="token punctuation">,</span> mMeasureBuffer<span class="token punctuation">)</span><span class="token punctuation">;</span>
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float relativeX <span class="token operator">=</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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float relativeY <span class="token operator">=</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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float width <span class="token operator">=</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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float height <span class="token operator">=</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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successCallback<span class="token punctuation">.</span><span class="token function">invoke<span class="token punctuation">(</span></span>relativeX<span class="token punctuation">,</span> relativeY<span class="token punctuation">,</span> width<span class="token punctuation">,</span> height<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IllegalViewOperationException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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errorCallback<span class="token punctuation">.</span><span class="token function">invoke<span class="token punctuation">(</span></span>e<span class="token punctuation">.</span><span class="token function">getMessage<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></div><p>This method would be accessed in JavaScript using:</p><div class="prism language-javascript">UIManager<span class="token punctuation">.</span><span class="token function">measureLayout<span class="token punctuation">(</span></span>
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<span class="token number">100</span><span class="token punctuation">,</span>
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<span class="token number">100</span><span class="token punctuation">,</span>
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<span class="token punctuation">(</span>msg<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> <span class="token punctuation">{</span>
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console<span class="token punctuation">.</span><span class="token function">log<span class="token punctuation">(</span></span>msg<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span><span class="token punctuation">,</span>
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<span class="token punctuation">(</span>x<span class="token punctuation">,</span> y<span class="token punctuation">,</span> width<span class="token punctuation">,</span> height<span class="token punctuation">)</span> <span class="token operator">=</span><span class="token operator">></span> <span class="token punctuation">{</span>
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console<span class="token punctuation">.</span><span class="token function">log<span class="token punctuation">(</span></span>x <span class="token operator">+</span> <span class="token string">':'</span> <span class="token operator">+</span> y <span class="token operator">+</span> <span class="token string">':'</span> <span class="token operator">+</span> width <span class="token operator">+</span> <span class="token string">':'</span> <span class="token operator">+</span> height<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">)</span><span class="token punctuation">;</span></div><p>A native module is supposed to invoke its callback only once. It can, however, store the callback and invoke it later.</p><p>It is very important to highlight that the callback is not invoked immediately after the native function completes - remember that bridge communication is asynchronous, and this too is tied to the run loop.</p><h3><a class="anchor" name="promises"></a>Promises <a class="hash-link" href="docs/native-modules-android.html#promises">#</a></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><div class="prism language-javascript">import com<span class="token punctuation">.</span>facebook<span class="token punctuation">.</span>react<span class="token punctuation">.</span>bridge<span class="token punctuation">.</span>Promise<span class="token punctuation">;</span>
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public class <span class="token class-name">UIManagerModule</span> extends <span class="token class-name">ReactContextBaseJavaModule</span> <span class="token punctuation">{</span>
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<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
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private static final String E_LAYOUT_ERROR <span class="token operator">=</span> <span class="token string">"E_LAYOUT_ERROR"</span><span class="token punctuation">;</span>
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@ReactMethod
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public void <span class="token function">measureLayout<span class="token punctuation">(</span></span>
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int tag<span class="token punctuation">,</span>
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int ancestorTag<span class="token punctuation">,</span>
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Promise promise<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span>
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<span class="token function">measureLayout<span class="token punctuation">(</span></span>tag<span class="token punctuation">,</span> ancestorTag<span class="token punctuation">,</span> mMeasureBuffer<span class="token punctuation">)</span><span class="token punctuation">;</span>
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WritableMap map <span class="token operator">=</span> Arguments<span class="token punctuation">.</span><span class="token function">createMap<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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map<span class="token punctuation">.</span><span class="token function">putDouble<span class="token punctuation">(</span></span><span class="token string">"relativeX"</span><span class="token punctuation">,</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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map<span class="token punctuation">.</span><span class="token function">putDouble<span class="token punctuation">(</span></span><span class="token string">"relativeY"</span><span class="token punctuation">,</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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map<span class="token punctuation">.</span><span class="token function">putDouble<span class="token punctuation">(</span></span><span class="token string">"width"</span><span class="token punctuation">,</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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map<span class="token punctuation">.</span><span class="token function">putDouble<span class="token punctuation">(</span></span><span class="token string">"height"</span><span class="token punctuation">,</span> PixelUtil<span class="token punctuation">.</span><span class="token function">toDIPFromPixel<span class="token punctuation">(</span></span>mMeasureBuffer<span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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promise<span class="token punctuation">.</span><span class="token function">resolve<span class="token punctuation">(</span></span>map<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IllegalViewOperationException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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promise<span class="token punctuation">.</span><span class="token function">reject<span class="token punctuation">(</span></span>E_LAYOUT_ERROR<span class="token punctuation">,</span> e<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span></div><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><div class="prism language-javascript">async <span class="token keyword">function</span> <span class="token function">measureLayout<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span>
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<span class="token keyword">var</span> <span class="token punctuation">{</span>
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relativeX<span class="token punctuation">,</span>
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|
relativeY<span class="token punctuation">,</span>
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width<span class="token punctuation">,</span>
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height<span class="token punctuation">,</span>
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<span class="token punctuation">}</span> <span class="token operator">=</span> await UIManager<span class="token punctuation">.</span><span class="token function">measureLayout<span class="token punctuation">(</span></span><span class="token number">100</span><span class="token punctuation">,</span> <span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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console<span class="token punctuation">.</span><span class="token function">log<span class="token punctuation">(</span></span>relativeX <span class="token operator">+</span> <span class="token string">':'</span> <span class="token operator">+</span> relativeY <span class="token operator">+</span> <span class="token string">':'</span> <span class="token operator">+</span> width <span class="token operator">+</span> <span class="token string">':'</span> <span class="token operator">+</span> height<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">e</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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console<span class="token punctuation">.</span><span class="token function">error<span class="token punctuation">(</span></span>e<span class="token punctuation">)</span><span class="token punctuation">;</span>
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|
<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token function">measureLayout<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span></div><h3><a class="anchor" name="threading"></a>Threading <a class="hash-link" href="docs/native-modules-android.html#threading">#</a></h3><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" name="getting-activity-result-from-startactivityforresult"></a>Getting activity result from <code>startActivityForResult</code> <a class="hash-link" href="docs/native-modules-android.html#getting-activity-result-from-startactivityforresult">#</a></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><div class="prism language-javascript">reactContext<span class="token punctuation">.</span><span class="token function">addActivityEventListener<span class="token punctuation">(</span></span>mActivityResultListener<span class="token punctuation">)</span><span class="token punctuation">;</span></div><p>Now you can listen to <code>onActivityResult</code> by implementing the following method:</p><div class="prism language-javascript">@Override
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|
public void <span class="token function">onActivityResult<span class="token punctuation">(</span></span>
|
|
final Activity activity<span class="token punctuation">,</span>
|
|
final int requestCode<span class="token punctuation">,</span>
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|
final int resultCode<span class="token punctuation">,</span>
|
|
final Intent intent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
|
|
<span class="token comment" spellcheck="true"> // Your logic here
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|
</span><span class="token punctuation">}</span></div><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><div class="prism language-javascript">public class <span class="token class-name">ImagePickerModule</span> extends <span class="token class-name">ReactContextBaseJavaModule</span> <span class="token punctuation">{</span>
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private static final int IMAGE_PICKER_REQUEST <span class="token operator">=</span> <span class="token number">467081</span><span class="token punctuation">;</span>
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|
private static final String E_ACTIVITY_DOES_NOT_EXIST <span class="token operator">=</span> <span class="token string">"E_ACTIVITY_DOES_NOT_EXIST"</span><span class="token punctuation">;</span>
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private static final String E_PICKER_CANCELLED <span class="token operator">=</span> <span class="token string">"E_PICKER_CANCELLED"</span><span class="token punctuation">;</span>
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|
private static final String E_FAILED_TO_SHOW_PICKER <span class="token operator">=</span> <span class="token string">"E_FAILED_TO_SHOW_PICKER"</span><span class="token punctuation">;</span>
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private static final String E_NO_IMAGE_DATA_FOUND <span class="token operator">=</span> <span class="token string">"E_NO_IMAGE_DATA_FOUND"</span><span class="token punctuation">;</span>
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private Promise mPickerPromise<span class="token punctuation">;</span>
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private final ActivityEventListener mActivityEventListener <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BaseActivityEventListener</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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@Override
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public void <span class="token function">onActivityResult<span class="token punctuation">(</span></span>Activity activity<span class="token punctuation">,</span> int requestCode<span class="token punctuation">,</span> int resultCode<span class="token punctuation">,</span> Intent intent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>requestCode <span class="token operator">==</span> IMAGE_PICKER_REQUEST<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>mPickerPromise <span class="token operator">!</span><span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>resultCode <span class="token operator">==</span> Activity<span class="token punctuation">.</span>RESULT_CANCELED<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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mPickerPromise<span class="token punctuation">.</span><span class="token function">reject<span class="token punctuation">(</span></span>E_PICKER_CANCELLED<span class="token punctuation">,</span> <span class="token string">"Image picker was cancelled"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>resultCode <span class="token operator">==</span> Activity<span class="token punctuation">.</span>RESULT_OK<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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Uri uri <span class="token operator">=</span> intent<span class="token punctuation">.</span><span class="token function">getData<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>uri <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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mPickerPromise<span class="token punctuation">.</span><span class="token function">reject<span class="token punctuation">(</span></span>E_NO_IMAGE_DATA_FOUND<span class="token punctuation">,</span> <span class="token string">"No image data found"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
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mPickerPromise<span class="token punctuation">.</span><span class="token function">resolve<span class="token punctuation">(</span></span>uri<span class="token punctuation">.</span><span class="token function">toString<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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mPickerPromise <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span><span class="token punctuation">;</span>
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public <span class="token function">ImagePickerModule<span class="token punctuation">(</span></span>ReactApplicationContext reactContext<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token function">super<span class="token punctuation">(</span></span>reactContext<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment" spellcheck="true"> // Add the listener for `onActivityResult`
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</span> reactContext<span class="token punctuation">.</span><span class="token function">addActivityEventListener<span class="token punctuation">(</span></span>mActivityEventListener<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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@Override
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public String <span class="token function">getName<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token keyword">return</span> <span class="token string">"ImagePickerModule"</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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@ReactMethod
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public void <span class="token function">pickImage<span class="token punctuation">(</span></span>final Promise promise<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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Activity currentActivity <span class="token operator">=</span> <span class="token function">getCurrentActivity<span class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">if</span> <span class="token punctuation">(</span>currentActivity <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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promise<span class="token punctuation">.</span><span class="token function">reject<span class="token punctuation">(</span></span>E_ACTIVITY_DOES_NOT_EXIST<span class="token punctuation">,</span> <span class="token string">"Activity doesn't exist"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token keyword">return</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment" spellcheck="true"> // Store the promise to resolve/reject when picker returns data
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</span> mPickerPromise <span class="token operator">=</span> promise<span class="token punctuation">;</span>
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<span class="token keyword">try</span> <span class="token punctuation">{</span>
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final Intent galleryIntent <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Intent</span><span class="token punctuation">(</span>Intent<span class="token punctuation">.</span>ACTION_PICK<span class="token punctuation">)</span><span class="token punctuation">;</span>
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galleryIntent<span class="token punctuation">.</span><span class="token function">setType<span class="token punctuation">(</span></span><span class="token string">"image/*"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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final Intent chooserIntent <span class="token operator">=</span> Intent<span class="token punctuation">.</span><span class="token function">createChooser<span class="token punctuation">(</span></span>galleryIntent<span class="token punctuation">,</span> <span class="token string">"Pick an image"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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currentActivity<span class="token punctuation">.</span><span class="token function">startActivityForResult<span class="token punctuation">(</span></span>chooserIntent<span class="token punctuation">,</span> IMAGE_PICKER_REQUEST<span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">Exception</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span>
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mPickerPromise<span class="token punctuation">.</span><span class="token function">reject<span class="token punctuation">(</span></span>E_FAILED_TO_SHOW_PICKER<span class="token punctuation">,</span> e<span class="token punctuation">)</span><span class="token punctuation">;</span>
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mPickerPromise <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span>
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<span class="token punctuation">}</span></div><h3><a class="anchor" name="listening-to-lifecycle-events"></a>Listening to LifeCycle events <a class="hash-link" href="docs/native-modules-android.html#listening-to-lifecycle-events">#</a></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><div class="prism language-javascript">reactContext<span class="token punctuation">.</span><span class="token function">addLifecycleEventListener<span class="token punctuation">(</span></span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span></div><p>Now you can listen to the activity's LifeCycle events by implementing the following methods:</p><div class="prism language-javascript">@Override
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public void <span class="token function">onHostResume<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment" spellcheck="true"> // Activity `onResume`
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</span><span class="token punctuation">}</span>
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@Override
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public void <span class="token function">onHostPause<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment" spellcheck="true"> // Activity `onPause`
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</span><span class="token punctuation">}</span>
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@Override
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public void <span class="token function">onHostDestroy<span class="token punctuation">(</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment" spellcheck="true"> // Activity `onDestroy`
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</span><span class="token punctuation">}</span></div></div><div class="docs-prevnext"><a class="docs-prev" href="docs/communication-ios.html#content">← Prev</a><a class="docs-next" href="docs/native-components-android.html#content">Next →</a></div><p class="edit-page-block">You can <a target="_blank" href="https://github.com/facebook/react-native/blob/master/docs/NativeModulesAndroid.md">edit the content above on GitHub</a> and send us a pull request!</p></div></section><footer class="nav-footer"><section class="sitemap"><a href="/react-native" class="nav-home"><img src="img/header_logo.png" alt="React Native" width="66" height="58"></a><div><h5><a href="docs/">Docs</a></h5><a href="docs/getting-started.html">Getting Started</a><a href="docs/tutorial.html">Tutorial</a><a href="docs/integration-with-existing-apps.html">Integration With Existing Apps</a><a href="docs/more-resources.html">More Resources</a></div><div><h5><a href="/react-native/support.html">Community</a></h5><a href="/react-native/showcase.html">Showcase</a><a href="http://www.meetup.com/topics/react-native/" target="_blank">Upcoming Events</a><a href="https://www.facebook.com/groups/react.native.community" target="_blank">Facebook Group</a><a href="https://twitter.com/reactnative" target="_blank">Twitter</a></div><div><h5><a href="/react-native/support.html">Help</a></h5><a href="http://stackoverflow.com/questions/tagged/react-native" target="_blank">Stack Overflow</a><a href="https://discord.gg/0ZcbPKXt5bZjGY5n">Reactiflux Chat</a><a href="/react-native/versions.html" target="_blank">Latest Releases</a><a href="https://react-native.canny.io/feature-requests" target="_blank">Feature Requests</a></div><div><h5>More</h5><a href="/react-native/blog">Blog</a><a href="https://github.com/facebook/react-native" target="_blank">GitHub</a><a href="http://facebook.github.io/react/" target="_blank">React</a></div></section><section class="newsletter"><div id="mc_embed_signup"><form action="//reactnative.us10.list-manage.com/subscribe/post?u=db0dd948e2b729ee62625b1a8&id=47cd41008f" method="post" id="mc-embedded-subscribe-form" name="mc-embedded-subscribe-form" class="validate" target="_blank" novalidate><div id="mc_embed_signup_scroll"><label for="mce-EMAIL"><h5>Get the React Native Newsletter</h5></label><input type="email" value="" name="EMAIL" class="email" id="mce-EMAIL" placeholder="email address" required><div style="position:absolute;left:-5000px;" aria-hidden="true"><input type="text" name="b_db0dd948e2b729ee62625b1a8_47cd41008f" tabindex="-1" value=""></div><div class="clear"><input type="submit" value="Sign up" name="subscribe" id="mc-embedded-subscribe" class="button"></div></div></form></div></section><a href="https://code.facebook.com/projects/" target="_blank" class="fbOpenSource"><img src="img/oss_logo.png" alt="Facebook Open Source" width="170" height="45"></a><section class="copyright">Copyright © 2017 Facebook Inc.</section></footer></div><div id="fb-root"></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><script>
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