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Android -- Messenger与Service

日期：2017-09-30点击：493收藏

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 { @Override public 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. */ @Override public 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' // value Message msg = Message .obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0); try { mService.send(msg); } catch (RemoteException e) { e.printStackTrace(); } } @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override protected void onStart() { super.onStart(); // Bind to the service bindService(new Intent(this, MessengerService.class), mConnection, Context.BIND_AUTO_CREATE); } @Override protected void onStop() { super.onStop(); // Unbind from the service if (mBound) { unbindService(mConnection); mBound = false; } } }