react-native/docs/headless-js-android.md

id, title, original_id

id	title	original_id
version-0.50-headless-js-android	headless-js-android	headless-js-android

Headless JS #

Project with Native Code Required

This page only applies to projects made with react-native init or to those made with Create React Native App which have since ejected. For more information about ejecting, please see the guide on the Create React Native App repository.

Headless JS is a way to run tasks in JavaScript while your app is in the background. It can be used, for example, to sync fresh data, handle push notifications, or play music.

The JS API #

A task is a simple async function that you register on AppRegistry, similar to registering React applications:

AppRegistry.registerHeadlessTask('SomeTaskName', () => require('SomeTaskName'));

Then, in SomeTaskName.js:

module.exports = async (taskData) => { // do stuff }

You can do anything in your task as long as it doesn't touch UI: network requests, timers and so on. Once your task completes (i.e. the promise is resolved), React Native will go into "paused" mode (unless there are other tasks running, or there is a foreground app).

The Java API #

Yes, this does still require some native code, but it's pretty thin. You need to extend HeadlessJsTaskService and override getTaskConfig, e.g.:

public class MyTaskService extends HeadlessJsTaskService {

@Override protected @Nullable HeadlessJsTaskConfig getTaskConfig(Intent intent) { Bundle extras = intent.getExtras(); if (extras != null) { return new HeadlessJsTaskConfig( "SomeTaskName", Arguments.fromBundle(extras), 5000, // timeout for the task false // optional: defines whether or not the task is allowed in foreground. Default is false ); } return null; } }

Then add the service to your AndroidManifest.xml file:

<service android:name="com.example.MyTaskService" />

Now, whenever you start your service, e.g. as a periodic task or in response to some system event / broadcast, JS will spin up, run your task, then spin down.

Example:

Intent service = new Intent(getApplicationContext(), MyTaskService.class); Bundle bundle = new Bundle();

bundle.putString("foo", "bar"); service.putExtras(bundle);

getApplicationContext().startService(service);

Caveats #

• 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 boolean argument to control this behaviour.
• If you start your service from a BroadcastReceiver, make sure to call HeadlessJsTaskService.acquireWakeLockNow() before returning from onReceive().

Example Usage #

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.

Following lines shows part of Android manifest file for registering broadcast receiver.

<receiver android:name=".NetworkChangeReceiver" > <intent-filter> <action android:name="android.net.conn.CONNECTIVITY_CHANGE" /> </intent-filter> </receiver>

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 putExta (keep in mind bundle can handle only parcelable values). In the end service is started and wakelock is acquired.

public class NetworkChangeReceiver extends BroadcastReceiver {

@Override
<span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">onReceive<span class="token punctuation">(</span></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" spellcheck="true">/**
      This part will be called everytime network connection is changed
      e.g. Connected -&gt; 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 class="token punctuation">(</span></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" spellcheck="true">/**
          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 class="token punctuation">(</span></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 class="token punctuation">(</span></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 class="token punctuation">(</span></span>serviceIntent<span class="token punctuation">)</span><span class="token punctuation">;</span>
        HeadlessJsTaskService<span class="token punctuation">.</span><span class="token function">acquireWakeLockNow<span class="token punctuation">(</span></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 class="token punctuation">(</span></span>Context context<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token comment" spellcheck="true">/**
      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 class="token punctuation">(</span></span>Context<span class="token punctuation">.</span>ACTIVITY_SERVICE<span class="token punctuation">)</span><span class="token punctuation">;</span>
    List<span class="token operator">&lt;</span>ActivityManager<span class="token punctuation">.</span>RunningAppProcessInfo<span class="token operator">&gt;</span> appProcesses <span class="token operator">=</span> 
    activityManager<span class="token punctuation">.</span><span class="token function">getRunningAppProcesses<span class="token punctuation">(</span></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 class="token punctuation">(</span></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 class="token punctuation">(</span></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 class="token punctuation">(</span></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 class="token punctuation">(</span></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 class="token punctuation">(</span></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 class="token punctuation">(</span></span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

}

← PreviousContinue Reading →

Improve this page by sending a pull request!