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19 lines
4.0 KiB
Markdown
19 lines
4.0 KiB
Markdown
---
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id: version-0.50-backhandler
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title: backhandler
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original_id: backhandler
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---
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<a id="content"></a><h1><a class="anchor" name="backhandler"></a>BackHandler <a class="hash-link" href="docs/backhandler.html#backhandler">#</a></h1><div><div><p>Detect hardware button presses for back navigation.</p><p>Android: Detect hardware back button presses, and programmatically invoke the default back button
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functionality to exit the app if there are no listeners or if none of the listeners return true.</p><p>tvOS: Detect presses of the menu button on the TV remote. (Still to be implemented:
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programmatically disable menu button handling
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functionality to exit the app if there are no listeners or if none of the listeners return true.)</p><p>iOS: Not applicable.</p><p>The event subscriptions are called in reverse order (i.e. last registered subscription first),
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and if one subscription returns true then subscriptions registered earlier will not be called.</p><p>Example:</p><div class="prism language-javascript">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" spellcheck="true"> // this.onMainScreen and this.goBack are just examples, you need to use your own implementation here
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</span><span class="token comment" spellcheck="true"> // Typically you would use the navigator here to go to the last state.
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</span>
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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 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 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></div></div><span><h3><a class="anchor" name="methods"></a>Methods <a class="hash-link" href="docs/backhandler.html#methods">#</a></h3><div class="props"><div class="prop"><h4 class="methodTitle"><a class="anchor" name="exitapp"></a><span class="methodType">static </span>exitApp<span class="methodType">()</span> <a class="hash-link" href="docs/backhandler.html#exitapp">#</a></h4></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="addeventlistener"></a><span class="methodType">static </span>addEventListener<span class="methodType">(eventName, handler)</span> <a class="hash-link" href="docs/backhandler.html#addeventlistener">#</a></h4></div><div class="prop"><h4 class="methodTitle"><a class="anchor" name="removeeventlistener"></a><span class="methodType">static </span>removeEventListener<span class="methodType">(eventName, handler)</span> <a class="hash-link" href="docs/backhandler.html#removeeventlistener">#</a></h4></div></div></span></div><p class="edit-page-block"><a target="_blank" href="https://github.com/facebook/react-native/blob/master/Libraries/Utilities/BackHandler.android.js">Improve this page</a> by sending a pull request!</p><div class="docs-prevnext"><a class="docs-prev" href="docs/backhandler.html#content">← Prev</a><a class="docs-next" href="docs/cameraroll.html#content">Next →</a></div> |