Android官方开发文档Training系列课程中文版：后台服务之响应IntentService的处理结果
原文地址：https://developer.android.com/training/run-background-service/report-status.html 这节课主要学习如何将IntentService中的执行结果返回给请求点。一种推荐的方式就是使用 LocalBroadcastManager来实现，它会将所广播的Intent限制在APP内部。 发送IntentService的处理结果 为了可以将IntentService的处理结果发送给其它组件，首先需要创建一个Intent对象，并将执行结果放入该Intent内。 接下来要做的就是：将刚才创建好的Intent通过LocalBroadcastManager.sendBroadcast()发送出去。但凡是对该Intent注册了的，那么发送该Intent都会收到结果。可以通过getInstance()获取LocalBroadcastManager的实例。 例子如下： public final class Constants { ... // Defines a custom Intent action public static final String BROADCAST_ACTION = "com.example.android.threadsample.BROADCAST"; ... // Defines the key for the status "extra" in an Intent public static final String EXTENDED_DATA_STATUS = "com.example.android.threadsample.STATUS"; ... } public class RSSPullService extends IntentService { ... /* * Creates a new Intent containing a Uri object * BROADCAST_ACTION is a custom Intent action */ Intent localIntent = new Intent(Constants.BROADCAST_ACTION) // Puts the status into the Intent .putExtra(Constants.EXTENDED_DATA_STATUS, status); // Broadcasts the Intent to receivers in this app. LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent); ... } 下一步就是如何处理接收到的Intent对象了。 接收IntentService的处理结果 如果需要接收广播出来的Intent，那么就需要用到BroadcastReceiver了。在BroadcastReceiver的实现类中重写onReceive()方法。当LocalBroadcastManager将相应的Intent对象广播出来后，那么该方法就会被自动回调。 举个例子： // Broadcast receiver for receiving status updates from the IntentService private class ResponseReceiver extends BroadcastReceiver { // Prevents instantiation private DownloadStateReceiver() { } // Called when the BroadcastReceiver gets an Intent it's registered to receive @ public void onReceive(Context context, Intent intent) { ... /* * Handle Intents here. */ ... } } 一旦定义好了BroadcastReceiver，那么就可以为其定义指定的意图过滤器了。要做到这些，需要创建一个IntentFilter。下面的代码演示了如何定义一个过滤器： // Class that displays photos public class DisplayActivity extends FragmentActivity { ... public void onCreate(Bundle stateBundle) { ... super.onCreate(stateBundle); ... // The filter's action is BROADCAST_ACTION IntentFilter mStatusIntentFilter = new IntentFilter( Constants.BROADCAST_ACTION); // Adds a data filter for the HTTP scheme mStatusIntentFilter.addDataScheme("http"); 为了将BroadcastReceiver以及IntentFilter注册到系统，需要先获取LocalBroadcastManager的实例，然后再调用它的registerReceiver()方法。下面的代码演示了这个过程： // Instantiates a new DownloadStateReceiver DownloadStateReceiver mDownloadStateReceiver = new DownloadStateReceiver(); // Registers the DownloadStateReceiver and its intent filters LocalBroadcastManager.getInstance(this).registerReceiver( mDownloadStateReceiver, mStatusIntentFilter); ... BroadcastReceiver可以同时处理多种类型的Intent对象，这项特性可以为每种Action定义不同的代码，而不需要专门去定义BroadcastReceiver。为同一个BroadcastReceiver定义另外的IntentFilter，只需再创建一个IntentFilter，然后再次注册一下就好： /* * Instantiates a new action filter. * No data filter is needed. */ statusIntentFilter = new IntentFilter(Constants.ACTION_ZOOM_IMAGE); ... // Registers the receiver with the new filter LocalBroadcastManager.getInstance(getActivity()).registerReceiver( mDownloadStateReceiver, mIntentFilter); 发送广播Intent并不会启动或者恢复Activity。就算是APP处于挂起状态(处于后台)也同样会接收到Intent。如果APP处于挂起状态的话，有任务完成需要通知到用户，那么可以使用Notification做到。绝不要启动Activity来响应接收到的Intent广播。
