Android -- Messenger与Service

如果你需要你的service和其他进程通信，那么你可以使用一个Messenger来提供这个接口。

这种方法允许你在不使用 AIDL的情况下，进行跨进程通信IPC。

实现步骤

下面是一个如何使用 Messenger的小总结：

　　1. service实现一个 Handler 接收客户端每一次调用的回调。

　　2. Handler 用来创建一个Messenger对象，它是一个Handler的引用。

　　3. Messenger创建一个 IBinder，service从 onBind()中把它返回给客户端。

　　4. 客户端使用这个IBinder来实例化Messenger （service的Handler的引用），客户端使用它来向service发送Message对象。

　　5. service在它的Handler中接收每一个Message对象，在它的 handleMessage()方法中。

Code

public class MessengerService extends Service
{/** Command to the service to display a message */static final int MSG_SAY_HELLO = 1;/*** Handler of incoming messages from clients.*/class IncomingHandler extends Handler{@Overridepublic void handleMessage(Message msg){switch (msg.what){case MSG_SAY_HELLO:Toast.makeText(getApplicationContext(), "hello!",Toast.LENGTH_SHORT).show();break;default:super.handleMessage(msg);}}}/*** Target we publish for clients to send messages to IncomingHandler.*/final Messenger mMessenger = new Messenger(new IncomingHandler());/*** When binding to the service, we return an interface to our messenger for* sending messages to the service.*/@Overridepublic IBinder onBind(Intent intent){Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show();return mMessenger.getBinder();}
}

　　注意 Handler中的 handleMessage() 方法是service接收到来的 Message并且决定做什么的地方。

　　客户端需要做的仅仅是创建一个基于service所返回的 IBinder的 Messenger，然后用 send()方法发送信息。

　　比如，这里有一个简单的activity和service绑定并且发送信息给service：

public class ActivityMessenger extends Activity
{/** Messenger for communicating with the service. */Messenger mService = null;/** Flag indicating whether we have called bind on the service. */boolean mBound;/*** Class for interacting with the main interface of the service.*/private ServiceConnection mConnection = new ServiceConnection(){public void onServiceConnected(ComponentName className, IBinder service){// This is called when the connection with the service has been// established, giving us the object we can use to// interact with the service. We are communicating with the// service using a Messenger, so here we get a client-side// representation of that from the raw IBinder object.mService = new Messenger(service);mBound = true;}public void onServiceDisconnected(ComponentName className){// This is called when the connection with the service has been// unexpectedly disconnected -- that is, its process crashed.mService = null;mBound = false;}};public void sayHello(View v){if (!mBound)return;// Create and send a message to the service, using a supported 'what'// valueMessage msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0);try{mService.send(msg);}catch (RemoteException e){e.printStackTrace();}}@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.main);}@Overrideprotected void onStart(){super.onStart();// Bind to the servicebindService(new Intent(this, MessengerService.class), mConnection,Context.BIND_AUTO_CREATE);}@Overrideprotected void onStop(){super.onStop();// Unbind from the serviceif (mBound){unbindService(mConnection);mBound = false;}}
}

　　注意这个例子并没有展示service如何响应客户端，如果你想要service响应，你需要在客户端中创建一个 Messenger。

　　然后当客户端接收到onServiceConnected()回调方法时，它会发送一个 Message到service，在它的send() 方法的replyTo参数中包含了客户端的Messenger。

我是天王盖地虎的分割线

本文转自我爱物联网博客园博客，原文链接：http://www.cnblogs.com/yydcdut/p/3950480.html，如需转载请自行联系原作者