本節講運行在後台服務裡的工作請求，如何向發送要求者報告狀態。推薦用LocalBroadcastManager發送和接收狀態，它限制了只有本app才能接收到廣播。
從IntentService彙報狀態
從IntentService發送工作請求狀態給其他組件，先建立一個包含狀態和資料的Intent。也可以添加action和URI到intent裡。
下一步，調用 LocalBroadcastManager.sendBroadcast()發送Intent,應用中所有註冊了接收該廣播的接收器都能收到。LocalBroadcastManager.getInstance()擷取LocalBroadcastManager執行個體。
複製代碼 代碼如下:
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);
...
}
下一步是接收廣播並處理。
接收來自IntentService的廣播
接收方式與普通的Broadcast一樣，用一個BroadcastReceiver的子類，實現BroadcastReceiver.onReceive()方法
複製代碼 代碼如下:
// 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.
*/
...
}
}
定義好了接收器類以後，定義過濾器，匹配指定的action,categorie,data.
複製代碼 代碼如下:
// 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");
...
註冊方式稍有不同，用LocalBroadcastManager.registerReceiver()。
複製代碼 代碼如下:
// Instantiates a new DownloadStateReceiver
DownloadStateReceiver mDownloadStateReceiver =
new DownloadStateReceiver();
// Registers the DownloadStateReceiver and its intent filters
LocalBroadcastManager.getInstance(this).registerReceiver(
mDownloadStateReceiver,
mStatusIntentFilter);
...
單個BroadcastReceiver可以處理多種類型的廣播，這個特性允許你根據不同的action運行不同的代碼，而無需為每個action定義一個BroadcastReceiver。
複製代碼 代碼如下:
/*
* 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);
發送廣播並不會啟動或恢複Activity.BroadcastReceiver讓Activity能夠接收處理資料，包括應用在背景時候，但不會強制app回到前台。如果你要在app在後台，對使用者不可見時，通知使用者一個事件發生，用Notification。絕對不要啟動一個Activity來響應廣播。
