本节讲运行在后台服务里的工作请求，如何向发送请求者报告状态。推荐用LocalBroadcastManager发送和接收状态，它限制了只有本app才能接收到广播。
从IntentService汇报状态
从IntentService发送工作请求状态给其他组件，先创建一个包含状态和数据的Intent。也可以添加action和URI到intent里。
下一步，调用 LocalBroadcastManager.sendBroadcast()发送Intent,应用中所有注册了接收该广播的接收器都能收到。LocalBroadcastManager.getInstance()获取LocalBroadcastManager实例。
代码如下:
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);
...
}
下一步是接收广播并处理。
接收来自IntentService的广播
接收方式与普通的Broadcast一样，用一个BroadcastReceiver的子类，实现BroadcastReceiver.onReceive()方法
代码如下:
// 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.
*/
...
}
}
定义好了接收器类以后，定义过滤器，匹配指定的action,categorie,data.
代码如下:
// 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");
...
注册方式稍有不同，用LocalBroadcastManager.registerReceiver()。
代码如下:
// Instantiates a new DownloadStateReceiver
DownloadStateReceiver mDownloadStateReceiver =
new DownloadStateReceiver();
// Registers the DownloadStateReceiver and its intent filters
LocalBroadcastManager.getInstance(this).registerReceiver(
mDownloadStateReceiver,
mStatusIntentFilter);
...
单个BroadcastReceiver可以处理多种类型的广播，这个特性允许你根据不同的action运行不同的代码，而无需为每个action定义一个BroadcastReceiver。
代码如下:
/*
* 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);
发送广播并不会启动或恢复Activity.BroadcastReceiver让Activity能够接收处理数据，包括应用在后台的时候，但不会强制app回到前台。如果你要在app在后台，对用户不可见时，通知用户一个事件发生，用Notification。绝对不要启动一个Activity来响应广播。