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);
...
}
AI 代码解读
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.
*/
...
}
}
AI 代码解读
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");
AI 代码解读
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);
...
AI 代码解读
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);
AI 代码解读
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。
