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<h2><a class="anchor" aria-hidden="true" id="the-js-api"></a><a href="#the-js-api" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>The JS API</h2>
<p>A task is a simple async function that you register on <code>AppRegistry</code>, similar to registering React applications:</p>
<pre><code class="hljs css language-javascript">AppRegistry<span class="token punctuation">.</span><span class="token function">registerHeadlessTask</span><span class="token punctuation">(</span><span class="token string">'SomeTaskName'</span><span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'SomeTaskName'</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<p>Then, in <code>SomeTaskName.js</code>:</p>
<pre><code class="hljs css language-javascript">module<span class="token punctuation">.</span>exports <span class="token operator">=</span> <span class="token keyword">async</span> <span class="token punctuation">(</span>taskData<span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">{</span>
<span class="token comment">// do stuff</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre>
<p>You can do anything in your task such as network requests, timers and so on, as long as it doesn't touch UI. Once your task completes (i.e. the promise is resolved), React Native will go into &quot;paused&quot; mode (unless there are other tasks running, or there is a foreground app).</p>
<h2><a class="anchor" aria-hidden="true" id="the-java-api"></a><a href="#the-java-api" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>The Java API</h2>
<p>Yes, this does still require some native code, but it's pretty thin. You need to extend <code>HeadlessJsTaskService</code> and override <code>getTaskConfig</code>, e.g.:</p>
<pre><code class="hljs css language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">MyTaskService</span> <span class="token keyword">extends</span> <span class="token class-name">HeadlessJsTaskService</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Override</span>
<span class="token keyword">protected</span> <span class="token annotation punctuation">@Nullable</span> HeadlessJsTaskConfig <span class="token function">getTaskConfig</span><span class="token punctuation">(</span>Intent intent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
Bundle extras <span class="token operator">=</span> intent<span class="token punctuation">.</span><span class="token function">getExtras</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>extras <span class="token operator">!=</span> null<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">HeadlessJsTaskConfig</span><span class="token punctuation">(</span>
<span class="token string">"SomeTaskName"</span><span class="token punctuation">,</span>
Arguments<span class="token punctuation">.</span><span class="token function">fromBundle</span><span class="token punctuation">(</span>extras<span class="token punctuation">)</span><span class="token punctuation">,</span>
<span class="token number">5000</span><span class="token punctuation">,</span> <span class="token comment">// timeout for the task</span>
<span class="token boolean">false</span> <span class="token comment">// optional: defines whether or not the task is allowed in foreground. Default is false</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> null<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
<p>Then add the service to your <code>AndroidManifest.xml</code> file:</p>
<pre><code class="hljs">&lt;service android:<span class="hljs-built_in">name</span>=<span class="hljs-string">"com.example.MyTaskService"</span> /&gt;
</code></pre>
<p>Now, whenever you <a href="https://developer.android.com/reference/android/content/Context.html#startService(android.content.Intent)">start your service</a>, e.g. as a periodic task or in response to some system event / broadcast, JS will spin up, run your task, then spin down.</p>
<p>Example:</p>
<pre><code class="hljs css language-java">Intent service <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Intent</span><span class="token punctuation">(</span><span class="token function">getApplicationContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> MyTaskService<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Bundle bundle <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Bundle</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
bundle<span class="token punctuation">.</span><span class="token function">putString</span><span class="token punctuation">(</span><span class="token string">"foo"</span><span class="token punctuation">,</span> <span class="token string">"bar"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
service<span class="token punctuation">.</span><span class="token function">putExtras</span><span class="token punctuation">(</span>bundle<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">getApplicationContext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">startService</span><span class="token punctuation">(</span>service<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="caveats"></a><a href="#caveats" 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>Caveats</h2>
<ul>
<li>By default, your app will crash if you try to run a task while the app is in the foreground. This is to prevent developers from shooting themselves in the foot by doing a lot of work in a task and slowing the UI. You can pass a fourth <code>boolean</code> argument to control this behaviour.</li>
<li>If you start your service from a <code>BroadcastReceiver</code>, make sure to call <code>HeadlessJsTaskService.acquireWakeLockNow()</code> before returning from <code>onReceive()</code>.</li>
</ul>
<h2><a class="anchor" aria-hidden="true" id="example-usage"></a><a href="#example-usage" 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 Usage</h2>
<p>Service can be started from Java API. First you need to decide when the service should be started and implement your solution accordingly. Here is a simple example that reacts to network connection change.</p>
<p>Following lines shows part of Android manifest file for registering broadcast receiver.</p>
<pre><code class="hljs css language-xml"><span class="hljs-tag">&lt;<span class="hljs-name">receiver</span> <span class="hljs-attr">android:name</span>=<span class="hljs-string">".NetworkChangeReceiver"</span> &gt;</span>
<span class="hljs-tag">&lt;<span class="hljs-name">intent-filter</span>&gt;</span>
<span class="hljs-tag">&lt;<span class="hljs-name">action</span> <span class="hljs-attr">android:name</span>=<span class="hljs-string">"android.net.conn.CONNECTIVITY_CHANGE"</span> /&gt;</span>
<span class="hljs-tag">&lt;/<span class="hljs-name">intent-filter</span>&gt;</span>
<span class="hljs-tag">&lt;/<span class="hljs-name">receiver</span>&gt;</span>
</code></pre>
<p>Broadcast receiver then handles intent that was broadcasted in onReceive function. This is a great place to check whether your app is on foreground or not. If app is not on foreground we can prepare our intent to be started, with no information or additional information bundled using <code>putExtra</code> (keep in mind bundle can handle only parcelable values). In the end service is started and wakelock is acquired.</p>
<pre><code class="hljs css language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">NetworkChangeReceiver</span> <span class="token keyword">extends</span> <span class="token class-name">BroadcastReceiver</span> <span class="token punctuation">{</span>
<span class="token annotation punctuation">@Override</span>
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">onReceive</span><span class="token punctuation">(</span><span class="token keyword">final</span> Context context<span class="token punctuation">,</span> <span class="token keyword">final</span> Intent intent<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">/**
This part will be called everytime network connection is changed
e.g. Connected -> Not Connected
**/</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">isAppOnForeground</span><span class="token punctuation">(</span><span class="token punctuation">(</span>context<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">/**
We will start our service and send extra info about
network connections
**/</span>
<span class="token keyword">boolean</span> hasInternet <span class="token operator">=</span> <span class="token function">isNetworkAvailable</span><span class="token punctuation">(</span>context<span class="token punctuation">)</span><span class="token punctuation">;</span>
Intent serviceIntent <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Intent</span><span class="token punctuation">(</span>context<span class="token punctuation">,</span> MyTaskService<span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
serviceIntent<span class="token punctuation">.</span><span class="token function">putExtra</span><span class="token punctuation">(</span><span class="token string">"hasInternet"</span><span class="token punctuation">,</span> hasInternet<span class="token punctuation">)</span><span class="token punctuation">;</span>
context<span class="token punctuation">.</span><span class="token function">startService</span><span class="token punctuation">(</span>serviceIntent<span class="token punctuation">)</span><span class="token punctuation">;</span>
HeadlessJsTaskService<span class="token punctuation">.</span><span class="token function">acquireWakeLockNow</span><span class="token punctuation">(</span>context<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">private</span> <span class="token keyword">boolean</span> <span class="token function">isAppOnForeground</span><span class="token punctuation">(</span>Context context<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token comment">/**
We need to check if app is in foreground otherwise the app will crash.
http://stackoverflow.com/questions/8489993/check-android-application-is-in-foreground-or-not
**/</span>
ActivityManager activityManager <span class="token operator">=</span> <span class="token punctuation">(</span>ActivityManager<span class="token punctuation">)</span> context<span class="token punctuation">.</span><span class="token function">getSystemService</span><span class="token punctuation">(</span>Context<span class="token punctuation">.</span>ACTIVITY_SERVICE<span class="token punctuation">)</span><span class="token punctuation">;</span>
List<span class="token generics function"><span class="token punctuation">&lt;</span>ActivityManager<span class="token punctuation">.</span>RunningAppProcessInfo<span class="token punctuation">></span></span> appProcesses <span class="token operator">=</span>
activityManager<span class="token punctuation">.</span><span class="token function">getRunningAppProcesses</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>appProcesses <span class="token operator">==</span> null<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">final</span> String packageName <span class="token operator">=</span> context<span class="token punctuation">.</span><span class="token function">getPackageName</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span>ActivityManager<span class="token punctuation">.</span>RunningAppProcessInfo appProcess <span class="token operator">:</span> appProcesses<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>appProcess<span class="token punctuation">.</span>importance <span class="token operator">==</span>
ActivityManager<span class="token punctuation">.</span>RunningAppProcessInfo<span class="token punctuation">.</span>IMPORTANCE_FOREGROUND <span class="token operator">&amp;&amp;</span>
appProcess<span class="token punctuation">.</span>processName<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>packageName<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">boolean</span> <span class="token function">isNetworkAvailable</span><span class="token punctuation">(</span>Context context<span class="token punctuation">)</span> <span class="token punctuation">{</span>
ConnectivityManager cm <span class="token operator">=</span> <span class="token punctuation">(</span>ConnectivityManager<span class="token punctuation">)</span>
context<span class="token punctuation">.</span><span class="token function">getSystemService</span><span class="token punctuation">(</span>Context<span class="token punctuation">.</span>CONNECTIVITY_SERVICE<span class="token punctuation">)</span><span class="token punctuation">;</span>
NetworkInfo netInfo <span class="token operator">=</span> cm<span class="token punctuation">.</span><span class="token function">getActiveNetworkInfo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> <span class="token punctuation">(</span>netInfo <span class="token operator">!=</span> null <span class="token operator">&amp;&amp;</span> netInfo<span class="token punctuation">.</span><span class="token function">isConnected</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre>
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