Broadcast Receiver

Broadcast Receiver用于接收并处理广播通知（broadcast announcements）。多数的广播是系统发起的，如地域变换、电量不足、来电来信等。程序也可以播放一个广播。程序可以有任意数量的 broadcast receivers来响应它觉得重要的通知。broadcast receiver可以通过多种方式通知用户：启动activity、使用NotificationManager、开启背景灯、振动设备、播放声音等，最 典型的是在状态栏显示一个图标，这样用户就可以点它打开看通知内容。

通常我们的某个应用或系统本身在某些事件（电池电量不足、来电来短信）来临时会广播一个Intent出去，我们可以利用注册一个Broadcast Receiver来监听到这些Intent并获取Intent中的数据。

 

1. 我们自己的程序主动广播Intent

final String BROADCAST = "com.forrest.action.mybroadcast";
Intent intent = new Intent(BROADCAST); // 对应setAction()
intent.putExtra("data_title", "来短信啦");
intent.putExtra("data_text", "美女你好，晚上可有空");
sendBroadcast(intent);

 

2.接收广播

接收broadcast需要注册一个Broadcast Receiver，并且要注册一个Intent Filter来制定Broadcase Receiver是对哪些Intent进行监听。

（1）注册Broadcast Receiver

一个Broadcast receiver只有一个简单的回调函数：onReceive(Context curContext, Intent broadcastMsg)，当一个广播消息被Receiver监听到时，Android会调用它的onReceive()方法，并将包含消息的Intent对象传给它。onReceive中代码的执行时间不要超过5s，否则android会弹出超时dialog。 此时是否另开一个线程来处理耗时的操作呢？

Receiver只在onReceive方法执行时是激活状态，只要onReceive一返回，Receiver就不再是激活状态了。Receiver进程是被一个激活状态的broadcast receiver所保护而不被系统终止的，一旦onReceive返回，Receiver进程broadcast receiver所保护而变为一个空进程，空进程是可以在任意时刻被终止的。这就带来了一个问题：当响应一个广播信息的处理十分耗时的时候，那么就应该把这个处理放在一个单独的线程里去执行，来保证主线程里的其他用户交互组件能够继续运行，而一旦这么做，当onReceive()唤起一个线程后就会马上返回，这时就会把Receiver进程放到被终止的境地。解决这个问题的方案是在onReceive()里开始一个Service，让这个Service去做这件事情，那么系统就会认为这个进程里还有活动正在进行。

（2）注册/注销Broadcast Receiver

1）在AndroidManifest.xml中注册

<receiver android:name="Receiver1">
	<intent-filter>
               <!-- 和Intent中的action对应 -->
		<action android:name="com.forrest.action.mybroadcast"/>
	</intent-filter>
</receiver>

 2）在代码中注册

IntentFilter filter = new IntentFilter("com.forrest.action.mybroadcast"); // 和广播中Intent的action对应
MyBroadcastReceiver br = new MyBroadcastReceiver();
registerReceiver(new MyBroadcastReceiver(), filter);

 3）注销

unregisterReceiver(br);

 

3. 示例代码

public class Receiver1 extends BroadcastReceiver {
	private Context context;
	public static final int NOTIFICATION_ID = 10001;
	
	public void onReceive(Context context, Intent intent) {
		this.context = context;
		showNotification();
	}
	
	private void showNotification() {
		Notification notification = new Notification(R.drawable.icon, "来电话啦...", System.currentTimeMillis());
		PendingIntent contentIntent = PendingIntent.getActivity(context, 0, new Intent(context, MainActivity.class), 0);
		notification.setLatestEventInfo(context, "来电话啦...嘿嘿", "赶紧接电话，否则误大事了", contentIntent);
		
		NotificationManager notificationManager = (NotificationManager) context.getSystemService(
				android.content.Context.NOTIFICATION_SERVICE);
		notificationManager.notify(NOTIFICATION_ID, notification);
	}
}

 

public class Receiver2 extends BroadcastReceiver {
	private Context context;
	
	@Override
	public void onReceive(Context context, Intent intent) {
		this.context = context;
		deleteNotification();
	}
	
	private void deleteNotification() {
		NotificationManager notificationManager = (NotificationManager) context.getSystemService(android.content.Context.NOTIFICATION_SERVICE);
		notificationManager.cancel(Receiver1.NOTIFICATION_ID);
	}
}

 

public class MainActivity extends Activity {
	private final String ACTION_SEND = "com.forrest.action.SENDMESSAGE",
						 ACTION_CLEAR = "com.forrest.action.CLEARNOTIFICATION";
	
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        ( (Button) findViewById(R.id.btn1) ).setOnClickListener(new OnClickListener() {
        	public void onClick(View v) {
        		clickMenuItem(ACTION_SEND);
        	}
        });
        ( (Button) findViewById(R.id.btn2) ).setOnClickListener(new OnClickListener() {
        	public void onClick(View v) {
        		clickMenuItem(ACTION_CLEAR);
        	}
        });
    }
    
    private void clickMenuItem(final String action) {
    	Intent intent = new Intent(action);
    	sendBroadcast(intent);
    }
}

 注册Broadcast Reciver

<application android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".MainActivity"
              android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <receiver android:name="Receiver1">
    	<intent-filter>
    		<action android:name="com.forrest.action.SENDMESSAGE"/>
    	</intent-filter>
    </receiver>
    <receiver android:name="Receiver2">
    	<intent-filter>
    		<action android:name="com.forrest.action.CLEARNOTIFICATION"/>
    	</intent-filter>
    </receiver>
</application>

 

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