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<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>BackHandler · React Native</title><meta name="viewport" content="width=device-width"/><meta name="generator" content="Docusaurus"/><meta name="description" content="The Backhandler API detects hardware button presses for back navigation, lets you register event listeners for the system's back action, and lets you control how your application responds. It is Android-only."/><meta name="docsearch:version" content="next"/><meta name="docsearch:language" content="en"/><meta property="og:title" content="BackHandler · React Native"/><meta property="og:type" content="website"/><meta property="og:url" content="https://reactnative.dev/"/><meta property="og:description" content="The Backhandler API detects hardware button presses for back navigation, lets you register event listeners for the system's back action, and lets you control how your application responds. It is Android-only."/><meta property="og:image" content="https://reactnative.dev/img/logo-og.png"/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://reactnative.dev/img/logo-og.png"/><link rel="shortcut icon" href="/img/favicon.ico"/><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://reactnative.dev/blog/atom.xml" title="React Native Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://reactnative.dev/blog/feed.xml" title="React Native Blog RSS Feed"/><script>
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</script></nav></div><div class="container mainContainer docsContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/facebook/react-native-website/blob/master/docs/backhandler.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 id="__docusaurus" class="postHeaderTitle">BackHandler</h1></header><article><div><span><p>The Backhandler API detects hardware button presses for back navigation, lets you register event listeners for the system's back action, and lets you control how your application responds. It is Android-only.</p>
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<p>The event subscriptions are called in reverse order (i.e. the last registered subscription is called first).</p>
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<ul>
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<li><strong>If one subscription returns true,</strong> then subscriptions registered earlier will not be called.</li>
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<li><strong>If no subscription returns true or none are registered,</strong> it programmatically invokes the default back button functionality to exit the app.</li>
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</ul>
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<blockquote>
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||
<p><strong>Warning for modal users:</strong> If your app shows an opened <code>Modal</code>, <code>BackHandler</code> will not publish any events (<a href="modal#onrequestclose">see <code>Modal</code> docs</a>).</p>
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||
</blockquote>
|
||
<h2><a class="anchor" aria-hidden="true" id="pattern"></a><a href="#pattern" 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>Pattern</h2>
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||
<pre><code class="hljs css language-jsx">BackHandler<span class="token punctuation">.</span><span class="token function">addEventListener</span><span class="token punctuation">(</span><span class="token string">'hardwareBackPress'</span><span class="token punctuation">,</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
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<span class="token comment">/**
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||
* this.onMainScreen and this.goBack are just examples,
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||
* you need to use your own implementation here.
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||
*
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||
* Typically you would use the navigator here to go to the last state.
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*/</span>
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||
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||
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">onMainScreen</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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<span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">goBack</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
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<span class="token comment">/**
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* When true is returned the event will not be bubbled up
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* & no other back action will execute
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*/</span>
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<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
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<span class="token punctuation">}</span>
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<span class="token comment">/**
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||
* Returning false will let the event to bubble up & let other event listeners
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||
* or the system's default back action to be executed.
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||
*/</span>
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||
<span class="token keyword">return</span> <span class="token boolean">false</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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||
</code></pre>
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||
<h2><a class="anchor" aria-hidden="true" id="example"></a><a href="#example" 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>Example</h2>
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||
<p>The following example implements a scenario where you confirm if the user wants to exit the app:</p>
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||
<div class="toggler">
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||
<ul role="tablist" class="toggle-syntax">
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||
<li id="functional" class="button-functional" aria-selected="false" role="tab" tabindex="0" aria-controls="functionaltab" onclick="displayTabs('syntax', 'functional')">
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||
Function Component Example
|
||
</li>
|
||
<li id="classical" class="button-classical" aria-selected="false" role="tab" tabindex="0" aria-controls="classicaltab" onclick="displayTabs('syntax', 'classical')">
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Class Component Example
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||
</li>
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||
</ul>
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</div>
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<p><block class="functional syntax" /></p>
|
||
<div class="snack-player"><div class="mobile-friendly-snack" style="display: none"><pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> React, { useEffect } <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
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<span class="hljs-keyword">import</span> { Text, View, StyleSheet, BackHandler, Alert } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-native"</span>;
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<span class="hljs-keyword">const</span> App = <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
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useEffect(<span class="hljs-function"><span class="hljs-params">()</span> =></span> {
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<span class="hljs-keyword">const</span> backAction = <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
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Alert.alert(<span class="hljs-string">"Hold on!"</span>, <span class="hljs-string">"Are you sure you want to go back?"</span>, [
|
||
{
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||
<span class="hljs-attr">text</span>: <span class="hljs-string">"Cancel"</span>,
|
||
<span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> <span class="hljs-literal">null</span>,
|
||
<span class="hljs-attr">style</span>: <span class="hljs-string">"cancel"</span>
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||
},
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||
{ <span class="hljs-attr">text</span>: <span class="hljs-string">"YES"</span>, <span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> BackHandler.exitApp() }
|
||
]);
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||
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
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||
};
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||
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||
<span class="hljs-keyword">const</span> backHandler = BackHandler.addEventListener(
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<span class="hljs-string">"hardwareBackPress"</span>,
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backAction
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||
);
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||
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<span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-params">()</span> =></span> backHandler.remove();
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}, []);
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<span class="hljs-keyword">return</span> (
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||
<span class="xml"><span class="hljs-tag"><<span class="hljs-name">View</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.container}</span>></span>
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<span class="hljs-tag"><<span class="hljs-name">Text</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.text}</span>></span>Click Back button!<span class="hljs-tag"></<span class="hljs-name">Text</span>></span>
|
||
<span class="hljs-tag"></<span class="hljs-name">View</span>></span></span>
|
||
);
|
||
};
|
||
|
||
<span class="hljs-keyword">const</span> styles = StyleSheet.create({
|
||
<span class="hljs-attr">container</span>: {
|
||
<span class="hljs-attr">flex</span>: <span class="hljs-number">1</span>,
|
||
<span class="hljs-attr">alignItems</span>: <span class="hljs-string">"center"</span>,
|
||
<span class="hljs-attr">justifyContent</span>: <span class="hljs-string">"center"</span>
|
||
},
|
||
<span class="hljs-attr">text</span>: {
|
||
<span class="hljs-attr">fontSize</span>: <span class="hljs-number">18</span>,
|
||
<span class="hljs-attr">fontWeight</span>: <span class="hljs-string">"bold"</span>
|
||
}
|
||
});
|
||
|
||
<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> App;
|
||
</code></pre></div><div class="desktop-friendly-snack" style="margin-top: 15px; margin-bottom: 15px"><div
|
||
data-snack-name="BackHandler"
|
||
data-snack-description="Example usage"
|
||
data-snack-code="import%20React%2C%20%7B%20useEffect%20%7D%20from%20%22react%22%3B%0Aimport%20%7B%20Text%2C%20View%2C%20StyleSheet%2C%20BackHandler%2C%20Alert%20%7D%20from%20%22react-native%22%3B%0A%0Aconst%20App%20%3D%20()%20%3D%3E%20%7B%0A%20%20useEffect(()%20%3D%3E%20%7B%0A%20%20%20%20const%20backAction%20%3D%20()%20%3D%3E%20%7B%0A%20%20%20%20%20%20Alert.alert(%22Hold%20on!%22%2C%20%22Are%20you%20sure%20you%20want%20to%20go%20back%3F%22%2C%20%5B%0A%20%20%20%20%20%20%20%20%7B%0A%20%20%20%20%20%20%20%20%20%20text%3A%20%22Cancel%22%2C%0A%20%20%20%20%20%20%20%20%20%20onPress%3A%20()%20%3D%3E%20null%2C%0A%20%20%20%20%20%20%20%20%20%20style%3A%20%22cancel%22%0A%20%20%20%20%20%20%20%20%7D%2C%0A%20%20%20%20%20%20%20%20%7B%20text%3A%20%22YES%22%2C%20onPress%3A%20()%20%3D%3E%20BackHandler.exitApp()%20%7D%0A%20%20%20%20%20%20%5D)%3B%0A%20%20%20%20%20%20return%20true%3B%0A%20%20%20%20%7D%3B%0A%0A%20%20%20%20const%20backHandler%20%3D%20BackHandler.addEventListener(%0A%20%20%20%20%20%20%22hardwareBackPress%22%2C%0A%20%20%20%20%20%20backAction%0A%20%20%20%20)%3B%0A%0A%20%20%20%20return%20()%20%3D%3E%20backHandler.remove()%3B%0A%20%20%7D%2C%20%5B%5D)%3B%0A%0A%20%20return%20(%0A%20%20%20%20%3CView%20style%3D%7Bstyles.container%7D%3E%0A%20%20%20%20%20%20%3CText%20style%3D%7Bstyles.text%7D%3EClick%20Back%20button!%3C%2FText%3E%0A%20%20%20%20%3C%2FView%3E%0A%20%20)%3B%0A%7D%3B%0A%0Aconst%20styles%20%3D%20StyleSheet.create(%7B%0A%20%20container%3A%20%7B%0A%20%20%20%20flex%3A%201%2C%0A%20%20%20%20alignItems%3A%20%22center%22%2C%0A%20%20%20%20justifyContent%3A%20%22center%22%0A%20%20%7D%2C%0A%20%20text%3A%20%7B%0A%20%20%20%20fontSize%3A%2018%2C%0A%20%20%20%20fontWeight%3A%20%22bold%22%0A%20%20%7D%0A%7D)%3B%0A%0Aexport%20default%20App%3B%0A"
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data-snack-platform="web"
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data-snack-supported-platforms=android
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data-snack-preview="true"
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style="
|
||
overflow: hidden;
|
||
background: #fafafa;
|
||
border: 1px solid rgba(0,0,0,.16);
|
||
border-radius: 4px;
|
||
height: 514px;
|
||
width: 100%;
|
||
"
|
||
></div></div></div><p><block class="classical syntax" /></p>
|
||
<div class="snack-player"><div class="mobile-friendly-snack" style="display: none"><pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> React, { Component } <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
|
||
<span class="hljs-keyword">import</span> { Text, View, StyleSheet, BackHandler, Alert } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-native"</span>;
|
||
|
||
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">App</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">Component</span> </span>{
|
||
backAction = <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
|
||
Alert.alert(<span class="hljs-string">"Hold on!"</span>, <span class="hljs-string">"Are you sure you want to go back?"</span>, [
|
||
{
|
||
<span class="hljs-attr">text</span>: <span class="hljs-string">"Cancel"</span>,
|
||
<span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> <span class="hljs-literal">null</span>,
|
||
<span class="hljs-attr">style</span>: <span class="hljs-string">"cancel"</span>
|
||
},
|
||
{ <span class="hljs-attr">text</span>: <span class="hljs-string">"YES"</span>, <span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> BackHandler.exitApp() }
|
||
]);
|
||
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
|
||
};
|
||
|
||
componentDidMount() {
|
||
<span class="hljs-keyword">this</span>.backHandler = BackHandler.addEventListener(
|
||
<span class="hljs-string">"hardwareBackPress"</span>,
|
||
<span class="hljs-keyword">this</span>.backAction
|
||
);
|
||
}
|
||
|
||
componentWillUnmount() {
|
||
<span class="hljs-keyword">this</span>.backHandler.remove();
|
||
}
|
||
|
||
render() {
|
||
<span class="hljs-keyword">return</span> (
|
||
<span class="xml"><span class="hljs-tag"><<span class="hljs-name">View</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.container}</span>></span>
|
||
<span class="hljs-tag"><<span class="hljs-name">Text</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.text}</span>></span>Click Back button!<span class="hljs-tag"></<span class="hljs-name">Text</span>></span>
|
||
<span class="hljs-tag"></<span class="hljs-name">View</span>></span></span>
|
||
);
|
||
}
|
||
};
|
||
|
||
<span class="hljs-keyword">const</span> styles = StyleSheet.create({
|
||
<span class="hljs-attr">container</span>: {
|
||
<span class="hljs-attr">flex</span>: <span class="hljs-number">1</span>,
|
||
<span class="hljs-attr">alignItems</span>: <span class="hljs-string">"center"</span>,
|
||
<span class="hljs-attr">justifyContent</span>: <span class="hljs-string">"center"</span>
|
||
},
|
||
<span class="hljs-attr">text</span>: {
|
||
<span class="hljs-attr">fontSize</span>: <span class="hljs-number">18</span>,
|
||
<span class="hljs-attr">fontWeight</span>: <span class="hljs-string">"bold"</span>
|
||
}
|
||
});
|
||
|
||
<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> App;
|
||
</code></pre></div><div class="desktop-friendly-snack" style="margin-top: 15px; margin-bottom: 15px"><div
|
||
data-snack-name="BackHandler"
|
||
data-snack-description="Example usage"
|
||
data-snack-code="import%20React%2C%20%7B%20Component%20%7D%20from%20%22react%22%3B%0Aimport%20%7B%20Text%2C%20View%2C%20StyleSheet%2C%20BackHandler%2C%20Alert%20%7D%20from%20%22react-native%22%3B%0A%0Aclass%20App%20extends%20Component%20%7B%0A%20%20backAction%20%3D%20()%20%3D%3E%20%7B%0A%20%20%20%20Alert.alert(%22Hold%20on!%22%2C%20%22Are%20you%20sure%20you%20want%20to%20go%20back%3F%22%2C%20%5B%0A%20%20%20%20%20%20%7B%0A%20%20%20%20%20%20%20%20text%3A%20%22Cancel%22%2C%0A%20%20%20%20%20%20%20%20onPress%3A%20()%20%3D%3E%20null%2C%0A%20%20%20%20%20%20%20%20style%3A%20%22cancel%22%0A%20%20%20%20%20%20%7D%2C%0A%20%20%20%20%20%20%7B%20text%3A%20%22YES%22%2C%20onPress%3A%20()%20%3D%3E%20BackHandler.exitApp()%20%7D%0A%20%20%20%20%5D)%3B%0A%20%20%20%20return%20true%3B%0A%20%20%7D%3B%0A%0A%20%20componentDidMount()%20%7B%0A%20%20%20%20this.backHandler%20%3D%20BackHandler.addEventListener(%0A%20%20%20%20%20%20%22hardwareBackPress%22%2C%0A%20%20%20%20%20%20this.backAction%0A%20%20%20%20)%3B%0A%20%20%7D%0A%0A%20%20componentWillUnmount()%20%7B%0A%20%20%20%20this.backHandler.remove()%3B%0A%20%20%7D%0A%0A%20%20render()%20%7B%0A%20%20%20%20return%20(%0A%20%20%20%20%20%20%3CView%20style%3D%7Bstyles.container%7D%3E%0A%20%20%20%20%20%20%20%20%3CText%20style%3D%7Bstyles.text%7D%3EClick%20Back%20button!%3C%2FText%3E%0A%20%20%20%20%20%20%3C%2FView%3E%0A%20%20%20%20)%3B%0A%20%20%7D%0A%7D%3B%0A%0Aconst%20styles%20%3D%20StyleSheet.create(%7B%0A%20%20container%3A%20%7B%0A%20%20%20%20flex%3A%201%2C%0A%20%20%20%20alignItems%3A%20%22center%22%2C%0A%20%20%20%20justifyContent%3A%20%22center%22%0A%20%20%7D%2C%0A%20%20text%3A%20%7B%0A%20%20%20%20fontSize%3A%2018%2C%0A%20%20%20%20fontWeight%3A%20%22bold%22%0A%20%20%7D%0A%7D)%3B%0A%0Aexport%20default%20App%3B%0A"
|
||
data-snack-platform="web"
|
||
data-snack-supported-platforms=android
|
||
data-snack-preview="true"
|
||
style="
|
||
overflow: hidden;
|
||
background: #fafafa;
|
||
border: 1px solid rgba(0,0,0,.16);
|
||
border-radius: 4px;
|
||
height: 514px;
|
||
width: 100%;
|
||
"
|
||
></div></div></div><p><block class="endBlock syntax" /></p>
|
||
<p><code>BackHandler.addEventListener</code> creates an event listener & returns a <code>NativeEventSubscription</code> object which should be cleared using <code>NativeEventSubscription.remove</code> method.</p>
|
||
<p>Additionally <code>BackHandler.removeEventListener</code> can also be used to clear the event listener. Ensure the callback has the reference to the same function used in the <code>addEventListener</code> call as shown the following example ﹣</p>
|
||
<div class="toggler">
|
||
<ul role="tablist" class="toggle-syntax">
|
||
<li id="functional" class="button-functional" aria-selected="false" role="tab" tabindex="0" aria-controls="functionaltab" onclick="displayTabs('syntax', 'functional')">
|
||
Function Component Example
|
||
</li>
|
||
<li id="classical" class="button-classical" aria-selected="false" role="tab" tabindex="0" aria-controls="classicaltab" onclick="displayTabs('syntax', 'classical')">
|
||
Class Component Example
|
||
</li>
|
||
</ul>
|
||
</div>
|
||
<p><block class="functional syntax" /></p>
|
||
<div class="snack-player"><div class="mobile-friendly-snack" style="display: none"><pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> React, { useEffect } <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
|
||
<span class="hljs-keyword">import</span> { Text, View, StyleSheet, BackHandler, Alert } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-native"</span>;
|
||
|
||
<span class="hljs-keyword">const</span> App = <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
|
||
<span class="hljs-keyword">const</span> backAction = <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
|
||
Alert.alert(<span class="hljs-string">"Hold on!"</span>, <span class="hljs-string">"Are you sure you want to go back?"</span>, [
|
||
{
|
||
<span class="hljs-attr">text</span>: <span class="hljs-string">"Cancel"</span>,
|
||
<span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> <span class="hljs-literal">null</span>,
|
||
<span class="hljs-attr">style</span>: <span class="hljs-string">"cancel"</span>
|
||
},
|
||
{ <span class="hljs-attr">text</span>: <span class="hljs-string">"YES"</span>, <span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> BackHandler.exitApp() }
|
||
]);
|
||
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
|
||
};
|
||
|
||
useEffect(<span class="hljs-function"><span class="hljs-params">()</span> =></span> {
|
||
BackHandler.addEventListener(<span class="hljs-string">"hardwareBackPress"</span>, backAction);
|
||
|
||
<span class="hljs-keyword">return</span> <span class="hljs-function"><span class="hljs-params">()</span> =></span>
|
||
BackHandler.removeEventListener(<span class="hljs-string">"hardwareBackPress"</span>, backAction);
|
||
}, []);
|
||
|
||
<span class="hljs-keyword">return</span> (
|
||
<span class="xml"><span class="hljs-tag"><<span class="hljs-name">View</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.container}</span>></span>
|
||
<span class="hljs-tag"><<span class="hljs-name">Text</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.text}</span>></span>Click Back button!<span class="hljs-tag"></<span class="hljs-name">Text</span>></span>
|
||
<span class="hljs-tag"></<span class="hljs-name">View</span>></span></span>
|
||
);
|
||
};
|
||
|
||
<span class="hljs-keyword">const</span> styles = StyleSheet.create({
|
||
<span class="hljs-attr">container</span>: {
|
||
<span class="hljs-attr">flex</span>: <span class="hljs-number">1</span>,
|
||
<span class="hljs-attr">alignItems</span>: <span class="hljs-string">"center"</span>,
|
||
<span class="hljs-attr">justifyContent</span>: <span class="hljs-string">"center"</span>
|
||
},
|
||
<span class="hljs-attr">text</span>: {
|
||
<span class="hljs-attr">fontSize</span>: <span class="hljs-number">18</span>,
|
||
<span class="hljs-attr">fontWeight</span>: <span class="hljs-string">"bold"</span>
|
||
}
|
||
});
|
||
|
||
<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> App;
|
||
</code></pre></div><div class="desktop-friendly-snack" style="margin-top: 15px; margin-bottom: 15px"><div
|
||
data-snack-name="BackHandler"
|
||
data-snack-description="Example usage"
|
||
data-snack-code="import%20React%2C%20%7B%20useEffect%20%7D%20from%20%22react%22%3B%0Aimport%20%7B%20Text%2C%20View%2C%20StyleSheet%2C%20BackHandler%2C%20Alert%20%7D%20from%20%22react-native%22%3B%0A%0Aconst%20App%20%3D%20()%20%3D%3E%20%7B%0A%20%20const%20backAction%20%3D%20()%20%3D%3E%20%7B%0A%20%20%20%20Alert.alert(%22Hold%20on!%22%2C%20%22Are%20you%20sure%20you%20want%20to%20go%20back%3F%22%2C%20%5B%0A%20%20%20%20%20%20%7B%0A%20%20%20%20%20%20%20%20text%3A%20%22Cancel%22%2C%0A%20%20%20%20%20%20%20%20onPress%3A%20()%20%3D%3E%20null%2C%0A%20%20%20%20%20%20%20%20style%3A%20%22cancel%22%0A%20%20%20%20%20%20%7D%2C%0A%20%20%20%20%20%20%7B%20text%3A%20%22YES%22%2C%20onPress%3A%20()%20%3D%3E%20BackHandler.exitApp()%20%7D%0A%20%20%20%20%5D)%3B%0A%20%20%20%20return%20true%3B%0A%20%20%7D%3B%0A%0A%20%20useEffect(()%20%3D%3E%20%7B%0A%20%20%20%20BackHandler.addEventListener(%22hardwareBackPress%22%2C%20backAction)%3B%0A%0A%20%20%20%20return%20()%20%3D%3E%0A%20%20%20%20%20%20BackHandler.removeEventListener(%22hardwareBackPress%22%2C%20backAction)%3B%0A%20%20%7D%2C%20%5B%5D)%3B%0A%0A%20%20return%20(%0A%20%20%20%20%3CView%20style%3D%7Bstyles.container%7D%3E%0A%20%20%20%20%20%20%3CText%20style%3D%7Bstyles.text%7D%3EClick%20Back%20button!%3C%2FText%3E%0A%20%20%20%20%3C%2FView%3E%0A%20%20)%3B%0A%7D%3B%0A%0Aconst%20styles%20%3D%20StyleSheet.create(%7B%0A%20%20container%3A%20%7B%0A%20%20%20%20flex%3A%201%2C%0A%20%20%20%20alignItems%3A%20%22center%22%2C%0A%20%20%20%20justifyContent%3A%20%22center%22%0A%20%20%7D%2C%0A%20%20text%3A%20%7B%0A%20%20%20%20fontSize%3A%2018%2C%0A%20%20%20%20fontWeight%3A%20%22bold%22%0A%20%20%7D%0A%7D)%3B%0A%0Aexport%20default%20App%3B%0A"
|
||
data-snack-platform="web"
|
||
data-snack-supported-platforms=android
|
||
data-snack-preview="true"
|
||
style="
|
||
overflow: hidden;
|
||
background: #fafafa;
|
||
border: 1px solid rgba(0,0,0,.16);
|
||
border-radius: 4px;
|
||
height: 514px;
|
||
width: 100%;
|
||
"
|
||
></div></div></div><p><block class="classical syntax" /></p>
|
||
<div class="snack-player"><div class="mobile-friendly-snack" style="display: none"><pre><code class="hljs css javascript"><span class="hljs-keyword">import</span> React, { Component } <span class="hljs-keyword">from</span> <span class="hljs-string">"react"</span>;
|
||
<span class="hljs-keyword">import</span> { Text, View, StyleSheet, BackHandler, Alert } <span class="hljs-keyword">from</span> <span class="hljs-string">"react-native"</span>;
|
||
|
||
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">App</span> <span class="hljs-keyword">extends</span> <span class="hljs-title">Component</span> </span>{
|
||
backAction = <span class="hljs-function"><span class="hljs-params">()</span> =></span> {
|
||
Alert.alert(<span class="hljs-string">"Hold on!"</span>, <span class="hljs-string">"Are you sure you want to go back?"</span>, [
|
||
{
|
||
<span class="hljs-attr">text</span>: <span class="hljs-string">"Cancel"</span>,
|
||
<span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> <span class="hljs-literal">null</span>,
|
||
<span class="hljs-attr">style</span>: <span class="hljs-string">"cancel"</span>
|
||
},
|
||
{ <span class="hljs-attr">text</span>: <span class="hljs-string">"YES"</span>, <span class="hljs-attr">onPress</span>: <span class="hljs-function"><span class="hljs-params">()</span> =></span> BackHandler.exitApp() }
|
||
]);
|
||
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
|
||
};
|
||
|
||
componentDidMount() {
|
||
BackHandler.addEventListener(<span class="hljs-string">"hardwareBackPress"</span>, <span class="hljs-keyword">this</span>.backAction);
|
||
}
|
||
|
||
componentWillUnmount() {
|
||
BackHandler.removeEventListener(<span class="hljs-string">"hardwareBackPress"</span>, <span class="hljs-keyword">this</span>.backAction);
|
||
}
|
||
|
||
render() {
|
||
<span class="hljs-keyword">return</span> (
|
||
<span class="xml"><span class="hljs-tag"><<span class="hljs-name">View</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.container}</span>></span>
|
||
<span class="hljs-tag"><<span class="hljs-name">Text</span> <span class="hljs-attr">style</span>=<span class="hljs-string">{styles.text}</span>></span>Click Back button!<span class="hljs-tag"></<span class="hljs-name">Text</span>></span>
|
||
<span class="hljs-tag"></<span class="hljs-name">View</span>></span></span>
|
||
);
|
||
}
|
||
};
|
||
|
||
<span class="hljs-keyword">const</span> styles = StyleSheet.create({
|
||
<span class="hljs-attr">container</span>: {
|
||
<span class="hljs-attr">flex</span>: <span class="hljs-number">1</span>,
|
||
<span class="hljs-attr">alignItems</span>: <span class="hljs-string">"center"</span>,
|
||
<span class="hljs-attr">justifyContent</span>: <span class="hljs-string">"center"</span>
|
||
},
|
||
<span class="hljs-attr">text</span>: {
|
||
<span class="hljs-attr">fontSize</span>: <span class="hljs-number">18</span>,
|
||
<span class="hljs-attr">fontWeight</span>: <span class="hljs-string">"bold"</span>
|
||
}
|
||
});
|
||
|
||
<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> App;
|
||
</code></pre></div><div class="desktop-friendly-snack" style="margin-top: 15px; margin-bottom: 15px"><div
|
||
data-snack-name="BackHandler"
|
||
data-snack-description="Example usage"
|
||
data-snack-code="import%20React%2C%20%7B%20Component%20%7D%20from%20%22react%22%3B%0Aimport%20%7B%20Text%2C%20View%2C%20StyleSheet%2C%20BackHandler%2C%20Alert%20%7D%20from%20%22react-native%22%3B%0A%0Aclass%20App%20extends%20Component%20%7B%0A%20%20backAction%20%3D%20()%20%3D%3E%20%7B%0A%20%20%20%20Alert.alert(%22Hold%20on!%22%2C%20%22Are%20you%20sure%20you%20want%20to%20go%20back%3F%22%2C%20%5B%0A%20%20%20%20%20%20%7B%0A%20%20%20%20%20%20%20%20text%3A%20%22Cancel%22%2C%0A%20%20%20%20%20%20%20%20onPress%3A%20()%20%3D%3E%20null%2C%0A%20%20%20%20%20%20%20%20style%3A%20%22cancel%22%0A%20%20%20%20%20%20%7D%2C%0A%20%20%20%20%20%20%7B%20text%3A%20%22YES%22%2C%20onPress%3A%20()%20%3D%3E%20BackHandler.exitApp()%20%7D%0A%20%20%20%20%5D)%3B%0A%20%20%20%20return%20true%3B%0A%20%20%7D%3B%0A%0A%20%20componentDidMount()%20%7B%0A%20%20%20%20BackHandler.addEventListener(%22hardwareBackPress%22%2C%20this.backAction)%3B%0A%20%20%7D%0A%0A%20%20componentWillUnmount()%20%7B%0A%20%20%20%20BackHandler.removeEventListener(%22hardwareBackPress%22%2C%20this.backAction)%3B%0A%20%20%7D%0A%0A%20%20render()%20%7B%0A%20%20%20%20return%20(%0A%20%20%20%20%20%20%3CView%20style%3D%7Bstyles.container%7D%3E%0A%20%20%20%20%20%20%20%20%3CText%20style%3D%7Bstyles.text%7D%3EClick%20Back%20button!%3C%2FText%3E%0A%20%20%20%20%20%20%3C%2FView%3E%0A%20%20%20%20)%3B%0A%20%20%7D%0A%7D%3B%0A%0Aconst%20styles%20%3D%20StyleSheet.create(%7B%0A%20%20container%3A%20%7B%0A%20%20%20%20flex%3A%201%2C%0A%20%20%20%20alignItems%3A%20%22center%22%2C%0A%20%20%20%20justifyContent%3A%20%22center%22%0A%20%20%7D%2C%0A%20%20text%3A%20%7B%0A%20%20%20%20fontSize%3A%2018%2C%0A%20%20%20%20fontWeight%3A%20%22bold%22%0A%20%20%7D%0A%7D)%3B%0A%0Aexport%20default%20App%3B%0A"
|
||
data-snack-platform="web"
|
||
data-snack-supported-platforms=android
|
||
data-snack-preview="true"
|
||
style="
|
||
overflow: hidden;
|
||
background: #fafafa;
|
||
border: 1px solid rgba(0,0,0,.16);
|
||
border-radius: 4px;
|
||
height: 514px;
|
||
width: 100%;
|
||
"
|
||
></div></div></div><p><block class="endBlock syntax" /></p>
|
||
<h2><a class="anchor" aria-hidden="true" id="usage-with-react-navigation"></a><a href="#usage-with-react-navigation" 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>Usage with React Navigation</h2>
|
||
<p>If you are using React Navigation to navigate across different screens, you can follow their guide on <a href="https://reactnavigation.org/docs/custom-android-back-button-handling/">Custom Android back button behaviour</a></p>
|
||
<h2><a class="anchor" aria-hidden="true" id="backhandler-hook"></a><a href="#backhandler-hook" 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>Backhandler hook</h2>
|
||
<p><a href="https://github.com/react-native-community/hooks#usebackhandler">React Native Hooks</a> has a nice <code>useBackHandler</code> hook which will simplify the process of setting up event listeners.</p>
|
||
<hr>
|
||
<h1><a class="anchor" aria-hidden="true" id="reference"></a><a href="#reference" 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>Reference</h1>
|
||
<h2><a class="anchor" aria-hidden="true" id="methods"></a><a href="#methods" 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>Methods</h2>
|
||
<h3><a class="anchor" aria-hidden="true" id="addeventlistener"></a><a href="#addeventlistener" 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><code>addEventListener()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token function">addEventListener</span><span class="token punctuation">(</span>eventName<span class="token punctuation">,</span> handler<span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="exitapp"></a><a href="#exitapp" 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><code>exitApp()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token function">exitApp</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="removeeventlistener"></a><a href="#removeeventlistener" 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><code>removeEventListener()</code></h3>
|
||
<pre><code class="hljs css language-jsx"><span class="token keyword">static</span> <span class="token function">removeEventListener</span><span class="token punctuation">(</span>eventName<span class="token punctuation">,</span> handler<span class="token punctuation">)</span>
|
||
</code></pre>
|
||
</span></div></article></div><div class="docs-prevnext"><a class="docs-prev button" href="/docs/next/usewindowdimensions"><span class="arrow-prev">← </span><span class="function-name-prevnext">useWindowDimensions</span></a><a class="docs-next button" href="/docs/next/permissionsandroid"><span class="function-name-prevnext">PermissionsAndroid</span><span class="arrow-next"> →</span></a></div></div></div><nav class="onPageNav"><ul class="toc-headings"><li><a href="#pattern">Pattern</a></li><li><a href="#example">Example</a></li><li><a href="#usage-with-react-navigation">Usage with React Navigation</a></li><li><a href="#backhandler-hook">Backhandler hook</a></li><li><a href="#methods">Methods</a><ul class="toc-headings"><li><a href="#addeventlistener"><code>addEventListener()</code></a></li><li><a href="#exitapp"><code>exitApp()</code></a></li><li><a href="#removeeventlistener"><code>removeEventListener()</code></a></li></ul></li></ul></nav></div><footer class="nav-footer" id="footer"><section class="sitemap"><div><h5>Docs</h5><a href="/docs/getting-started">Getting Started</a><a href="/docs/tutorial">Tutorial</a><a href="/docs/components-and-apis">Components and APIs</a><a href="/docs/more-resources">More Resources</a></div><div><h5>Community</h5><a href="/help">The React Native Community</a><a href="/showcase">Who's using React Native?</a><a href="https://stackoverflow.com/questions/tagged/react-native" target="_blank">Ask Questions on Stack Overflow</a><a href="https://github.com/facebook/react-native/blob/master/CONTRIBUTING.md">Contributor Guide</a><a href="https://dev.to/t/reactnative" target="_blank">DEV Community</a></div><div><h5>More Resources</h5><a href="/blog">Blog</a><a href="https://twitter.com/reactnative" target="_blank">Twitter</a><a href="https://github.com/facebook/react-native" target="_blank">GitHub</a><a href="https://reactjs.org" target="_blank">React</a></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 © 2020 Facebook Inc.</section></footer></div><script type="text/javascript" src="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.js"></script><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'));
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