Broadcast Receiver详解

http://wayfarer.iteye.com/blog/586157
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;@Overridepublic 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>