Android Broadcast

广播分为两种：标准广播和有序广播。

1. 系统广播

以监听网络变化为例子：

  public class MainActivity extends Activity{
      private IntentFilter intentFilter;
      private NetworkChangeFilter networkChangeReceiver;

    @Override
    protected void onCreate(Bundle saveInstaceState){
      ... 
      intentFilter = new IntentFIlter();
      intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
      networkChangeReceiver = new NetworkChangeFilter();
      registerReceiver(networkChangeReceiver, intentFilter); // 2. 注册接收者
    }

    @Override
    protected void onDestroy(){
      unregisterReceiver(networkChangeReceiver);
    }

    // 1. 接收者定义
    class NetworkChangeFilter implements BrodcastReceiver{
       @Override
       public void onReceive(Context context, Intent intent){
          // TODO
       }
    }
  }

// 3. Manfiest.xml申请权限
<use-premission android:name="android.permission.ACCESS_NETWORK_STATE" />

上面是动态注册，如果改成如下形式，那么就可实现静态注册开机启动：

  <android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
  <application >
    <receiver android:name=".BootCompleteReceiver">
      <intent-filter>
        <action android:name="android.intent.action_BOOT_COMPLETED" />
      </intent-filter>
  </application>

2. 自定义广播

自定义广播和系统广播类似，但需用户手动采用sendBroadcast触发：

1. 注册

 <application >
   <receiver android:name=".MyBroadcastReceiver">
     <intent-filter>
       <action android:name="com.examle.broadcast.MY_BROADCAST" />
     </intent-filter>
 </application>

2. 定义接收者

  class MyBroadcastReceiver implements BroadcastReceiver{
       @Override
       public void onReceive(Context context, Intent intent){
          // TODO
          // abortBroadcast();  如果是有序广播可以截断广播
       }
    }

3. 手动触发广播

  Intent intent = new Intent("com.examle.broadcast.MY_BROADCAST");
  sendBroadcast(intent);
  // sendOrderBroadcast(intent, null); 有序广播

3. 本地广播

前两种广播都是系统全局广播，即发出的广播可以被其他应用程序接收到，这样存在着安全性问题；本地广播可以解决这个问题。

  public class MainActivity extends Activity{
      private IntentFilter intentFilter;
      private LocalReceiver localReceiver;
      private LocalBroadcastManager localBroadcastManager;

    @Override
    protected void onCreate(Bundle savedInstanceState){
      ... 
      localBroadcastManager = LocalBroadcastManager.getInstance(this);
      intentFilter = new IntentFilter();   intentFilter.addAction("com.example.broadcast.LOCAL_BRODCAST");
      localReceiver = new LocalReceiver();
      localBroadcastManager.registerReceiver(localReceiver, intentFilter); 
  
      ...
      Intent intent = new Intent("com.example.broadcast.LOCAL_BRODCAST");
      localBroadcastManager.sendBroadcast(intent);
    }

    @Override
    protected void onDestroy(){
      unregisterReceiver(networkChangeReceiver);
    }

    class LocalReceiver implements BroadcastReceiver{
       @Override
       public void onReceive(Context context, Intent intent){
          // TODO
       }
    }
  }