如果把生活比喻为创作的意境，那么阅读就像阳光。 

本讲内容：举几个常见的例子加深一下对BroadcastReceiver广播的理解和应用：

一、开机启动服务

我们经常会有这样的应用场合，比如消息推送服务，需要实现开机启动的功能。要实现这个功能，我们就可以订阅系统“启动完成”这条广播，接收到这条广播后我们就可以启动自己的服务了。我们来看一下BootCompleteReceiver和MsgPushService的具体实现：

public class BootCompleteReceiver extends BroadcastReceiver {
	private static final String TAG = "MyReceiver";
	@Override
	public void onReceive(Context context, Intent intent) {
		Intent service =new Intent(context,MsgPushService.class);
		context.startService(service);
		Log.i(TAG, "Boot Complete. Starting MsgPushService...");  
	}
}

public class MsgPushService extends Service{
	private static final String TAG = "MyReceiver";
	@Override
	public IBinder onBind(Intent arg0) {
		return null;
	}
	@Override
	public void onCreate() {
		super.onCreate();
		Log.i(TAG, "onCreate called.");  
	}
	@Override
	public int onStartCommand(Intent intent, int flags, int startId) {
		Log.i(TAG, "onStartCommand called.");  
		return super.onStartCommand(intent, flags, startId);
	}
}

public class MainActivity extends Activity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
	}
}

 <!-- 开机广播接受者 -->
        <receiver android:name=".BootCompleteReceiver" >
            <intent-filter>
                <!-- 注册开机广播地址 -->
                <action android:name="android.intent.action.BOOT_COMPLETED" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </receiver>
        <!-- 消息推送服务 -->
        <service android:name=".MsgPushService" />

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" /> 

如果我们查看已运行的服务就会发现，MsgPushService已经运行起来了。

二、网络状态变化

譬如用户浏览网络信息时，网络突然断开，我们要及时地提醒用户网络已断开。要实现这个功能，下面就来实现一下这个功能：

public class NetworkStateReceiver extends BroadcastReceiver {
	private static final String TAG = "MyReceiver";
	@Override
	public void onReceive(Context context, Intent intent) {
		Log.i(TAG, "network state changed.");  
		if (!isNetworkAvailable(context)) {  
            Toast.makeText(context, "network disconnected!", 0).show();  
        }  
	}
	 
     /**
      * 网络是否可用 
      * @param context
      * @return
      */
   
    public static boolean isNetworkAvailable(Context context) {  
        ConnectivityManager mgr = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);  
        NetworkInfo[] info = mgr.getAllNetworkInfo();  
        if (info != null) {  
            for (int i = 0; i < info.length; i++) {  
                if (info[i].getState() == NetworkInfo.State.CONNECTED) {  
                    return true;  
                }  
            }  
        }  
        return false;  
    }  
}

注册

<receiver android:name=".NetworkStateReceiver" >
            <intent-filter>
                <action android:name="android.net.conn.CONNECTIVITY_CHANGE" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </receiver>

 <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/> 

三、电量变化

如果我们阅读软件，可能是全屏阅读，这个时候用户就看不到剩余的电量，我们就可以为他们提供电量的信息。要想做到这一点，我们需要接收一条电量变化的广播，然后获取百分比信息，我们就来实现以下：

public class BatteryChangedReceiver extends BroadcastReceiver {
	private static final String TAG = "MyReceiver";
	@Override
	public void onReceive(Context context, Intent intent) {
		int currLevel = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0); // 当前电量
		int total = intent.getIntExtra(BatteryManager.EXTRA_SCALE, 1); // 总电量
		int percent = currLevel * 100 / total;
		Log.i(TAG, "battery: " + percent + "%");
	}
}

 <receiver android:name=".BatteryChangedReceiver" >
            <intent-filter>
                <action android:name="android.intent.action.BATTERY_CHANGED" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
  </receiver>

public class BatteryChangedReceiver extends BroadcastReceiver {
	private static final String TAG = "MyReceiver";
	@Override
	public void onReceive(Context context, Intent intent) {
		Intent batteryIntent = getApplicationContext().registerReceiver(null,  
		        new IntentFilter(Intent.ACTION_BATTERY_CHANGED));  
		int currLevel = batteryIntent.getIntExtra(BatteryManager.EXTRA_LEVEL, 0);  
		int total = batteryIntent.getIntExtra(BatteryManager.EXTRA_SCALE, 1);  
		int percent = currLevel * 100 / total;  
		Log.i("battery", "battery: " + percent + "%");  
	}
	private Context getApplicationContext() {
		// TODO Auto-generated method stub
		return null;
	}
}

第六十讲：四大组件之BroadcastReceiver（三）