android Messenger 跨进程通讯

 Messenger:信使
官方文档解释：它引用了一个Handler对象，以便others能够向它发送消息(使用mMessenger.send(Message msg)方法)。该类允许跨进程间基于Message的通信(即两个进程间可以通过Message进行通信)，在服务端使用Handler创建一个Messenger，客户端持有这个Messenger就可以与服务端通信了。

以前我们使用Handler+Message的方式进行通信，都是在同一个进程中，从线程持有一个主线程的Handler对象，并向主线程发送消息。
而Android既然可以使用bindler机制进行跨进行通信，所以我们当然可以将Handler与bindler结合起来进行跨进程发送消息。
查看API就可以发现，Messenger就是这种方式的实现。
一般使用方法如下：
１。远程通过

mMessenger = new Messenger(mHandler)

mMessenger = new Messenger(mHandler) 

创建一个信使对象
２。客户端使用bindlerService请求连接远程
３。远程onBind方法返回一个bindler

return mMessenger.getBinder();

return mMessenger.getBinder(); 

4.客户端使用远程返回的bindler得到一个信使（即得到远程信使）
 

public void onServiceConnected(ComponentName name, IBinder service) {
    rMessenger = new Messenger(service);
　　　　　......
}

public void onServiceConnected(ComponentName name, IBinder service) {  
    rMessenger = new Messenger(service);  
　　　　　......  
}

 
这里虽然是new了一个Messenger，但我们查看它的实现
 

/**
 * Create a Messenger from a raw IBinder, which had previously been
 * retrieved with {@link #getBinder}.
 *
 * @param target The IBinder this Messenger should communicate with.
 */
public Messenger(IBinder target) {
    mTarget = IMessenger.Stub.asInterface(target);
}

/** 
 * Create a Messenger from a raw IBinder, which had previously been 
 * retrieved with {@link #getBinder}. 
 *  
 * @param target The IBinder this Messenger should communicate with. 
 */  
public Messenger(IBinder target) {  
    mTarget = IMessenger.Stub.asInterface(target);  
}  

发现它的mTarget是通过Aidl得到的，实际上就是远程创建的那个。
５。客户端可以使用这个远程信使对象向远程发送消息：

rMessenger.send(msg);

rMessenger.send(msg);

这样远程服务端的Handler对象就能收到消息了，然后可以在其
handlerMessage(Message msg)方法中进行处理。（该Handler对象就是第一步服务端创建Messenger时使用的参数mHandler）.

经过这５个步骤貌似只有客户端向服务端发送消息，这样的消息传递是单向的，那么如何实现双向传递呢？
首先需要在第５步稍加修改，在send(msg)前通过msm.replyTo = mMessenger将自己的信使设置到消息中，这样服务端接收到消息时同时也得到了客户端的信使对象了，然后服务端可以通过

//得到客户端的信使对象，并向它发送消息
cMessenger = msg.replyTo;
cMessenger.send(message);

//得到客户端的信使对象，并向它发送消息  
cMessenger = msg.replyTo;  
cMessenger.send(message); 

即完成了从服务端向客户端发送消息的功能，这样客服端可以在自己的Handler对象的handlerMessage方法中接收服务端发送来的message进行处理。
双向通信宣告完成。

下面改写ApiDemos工程实现Messenger通信
MessengerService.java

package com.xwangly.apidemo.app;

import java.util.Random;

import android.app.Service;
import android.content.Intent;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.util.Log;

public class MessengerService extends Service {
    private String TAG = "MessengerService";

    @Override
    public void onDestroy() {
        // TODO Auto-generated method stub
        Log.i(TAG, "onDestroy");
        cMessenger = null;
        super.onDestroy();
    }

    @Override
    public boolean onUnbind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(TAG, "onUnbind");
        return super.onUnbind(intent);
    }

    static final int MSG_REGISTER_CLIENT = 1;
    static final int MSG_UNREGISTER_CLIENT = 2;
    static final int MSG_SET_VALUE = 3;

    private Random random = new Random();

    private Handler mHandler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            // TODO Auto-generated method stub
            Log.i(TAG, "handleMessage");
            switch (msg.what) {
            case MSG_SET_VALUE:
                try {
                    Message message = Message.obtain(null,
                            MessengerService.MSG_SET_VALUE);
                    message.arg1 = random.nextInt(100);

                    //得到客户端的信使对象，并向它发送消息
                    cMessenger = msg.replyTo;
                    cMessenger.send(message);
                } catch (RemoteException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                break;
            default:
                super.handleMessage(msg);
            }

        }
    };

    /**
     * 自己的信使对象
     */
    private Messenger mMessenger = new Messenger(mHandler);

    /**
     * 客户的信使
     */
    private Messenger cMessenger;

    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(TAG, "onBind");
        //返回自己信使的bindler,以供客户端通过这个bindler得到服务端的信使对象（通过new Messenger(bindler)）
        return mMessenger.getBinder();
    }

    @Override
    public void onRebind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(TAG, "onRebind");

    }

}

  
package com.xwangly.apidemo.app;  
  
import java.util.Random;  
  
import android.app.Service;  
import android.content.Intent;  
import android.os.Handler;  
import android.os.IBinder;  
import android.os.Message;  
import android.os.Messenger;  
import android.os.RemoteException;  
import android.util.Log;  
  
public class MessengerService extends Service {  
    private String TAG = "MessengerService";  
  
    @Override  
    public void onDestroy() {  
        // TODO Auto-generated method stub  
        Log.i(TAG, "onDestroy");  
        cMessenger = null;  
        super.onDestroy();  
    }  
  
    @Override  
    public boolean onUnbind(Intent intent) {  
        // TODO Auto-generated method stub  
        Log.i(TAG, "onUnbind");  
        return super.onUnbind(intent);  
    }  
  
    static final int MSG_REGISTER_CLIENT = 1;  
    static final int MSG_UNREGISTER_CLIENT = 2;  
    static final int MSG_SET_VALUE = 3;  
  
    private Random random = new Random();  
  
    private Handler mHandler = new Handler() {  
  
        @Override  
        public void handleMessage(Message msg) {  
            // TODO Auto-generated method stub  
            Log.i(TAG, "handleMessage");  
            switch (msg.what) {  
            case MSG_SET_VALUE:  
                try {  
                    Message message = Message.obtain(null,  
                            MessengerService.MSG_SET_VALUE);  
                    message.arg1 = random.nextInt(100);  
                      
                    //得到客户端的信使对象，并向它发送消息  
                    cMessenger = msg.replyTo;  
                    cMessenger.send(message);  
                } catch (RemoteException e) {  
                    // TODO Auto-generated catch block  
                    e.printStackTrace();  
                }  
                break;  
            default:  
                super.handleMessage(msg);  
            }  
  
        }  
    };  
  
    /** 
     * 自己的信使对象 
     */  
    private Messenger mMessenger = new Messenger(mHandler);  
  
    /** 
     * 客户的信使 
     */  
    private Messenger cMessenger;  
  
    @Override  
    public IBinder onBind(Intent intent) {  
        // TODO Auto-generated method stub  
        Log.i(TAG, "onBind");  
        //返回自己信使的bindler,以供客户端通过这个bindler得到服务端的信使对象（通过new Messenger(bindler)）  
        return mMessenger.getBinder();  
    }  
  
    @Override  
    public void onRebind(Intent intent) {  
        // TODO Auto-generated method stub  
        Log.i(TAG, "onRebind");  
  
    }  
  
} 

MessengerServiceActivities.java

package com.xwangly.apidemo.app;

import com.xwangly.apidemo.R;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

public class MessengerServiceActivities {
    public static class Binding extends Activity implements
            View.OnClickListener {
        private String TAG = "Binding";

        TextView mCallbackText;

        private boolean isBound;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            // TODO Auto-generated method stub
            super.onCreate(savedInstanceState);
            setContentView(R.layout.messenger_service_binding);
            findViewById(R.id.bind).setOnClickListener(this);
            findViewById(R.id.unbind).setOnClickListener(this);

            mCallbackText = (TextView) findViewById(R.id.callback);
            mCallbackText.setText("Not attached.");

        }

        private Handler mHandler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                Log.i(TAG, "handleMessage");
                switch (msg.what) {
                case MessengerService.MSG_SET_VALUE:
                    mCallbackText.setText("Received from service: " + msg.arg1);
                    break;
                default:
                    super.handleMessage(msg);
                }
            }
        };

        /**
         * 自己的信使
         */
        private Messenger mMessenger;

        /**
         * 远程服务的信使
         */
        private Messenger rMessenger;

        private ServiceConnection connection = new ServiceConnection() {

            public void onServiceConnected(ComponentName name, IBinder service) {
                // TODO Auto-generated method stub
                Log.i(TAG, "onServiceConnected");
                rMessenger = new Messenger(service);
                mMessenger = new Messenger(mHandler);

                sendMessage();
            }


            public void onServiceDisconnected(ComponentName name) {
                // TODO Auto-generated method stub
                rMessenger = null;
            }
        };

        public void onClick(View v) {
            // TODO Auto-generated method stub
            Intent intent = new Intent(
                    "com.xwangly.apidemo.app.messenger_service");
            switch (v.getId()) {
            case R.id.bind:
                if (!isBound) {
                    isBound = bindService(intent, connection, BIND_AUTO_CREATE);
                    //isBound = true;
                }else {
                    sendMessage();
                }
                break;
            case R.id.unbind:
                if (isBound) {
                    unbindService(connection);
                    isBound = false;
                }
                break;
            default:
                break;
            }
        }

        /**
         * 使用服务端的信使向它发送一个消息。
         */
        private void sendMessage() {
            // TODO Auto-generated method stub
            Message message = Message.obtain(null, MessengerService.MSG_SET_VALUE);
            message.replyTo = mMessenger;
            try {
                rMessenger.send(message);
            } catch (RemoteException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

}

 
package com.xwangly.apidemo.app;  
  
import com.xwangly.apidemo.R;  
  
import android.app.Activity;  
import android.content.ComponentName;  
import android.content.Intent;  
import android.content.ServiceConnection;  
import android.os.Bundle;  
import android.os.Handler;  
import android.os.IBinder;  
import android.os.Message;  
import android.os.Messenger;  
import android.os.RemoteException;  
import android.util.Log;  
import android.view.View;  
import android.widget.TextView;  
  
public class MessengerServiceActivities {  
    public static class Binding extends Activity implements  
            View.OnClickListener {  
        private String TAG = "Binding";  
  
        TextView mCallbackText;  
  
        private boolean isBound;  
  
        @Override  
        protected void onCreate(Bundle savedInstanceState) {  
            // TODO Auto-generated method stub  
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.messenger_service_binding);  
            findViewById(R.id.bind).setOnClickListener(this);  
            findViewById(R.id.unbind).setOnClickListener(this);  
  
            mCallbackText = (TextView) findViewById(R.id.callback);  
            mCallbackText.setText("Not attached.");  
  
        }  
  
        private Handler mHandler = new Handler() {  
            @Override  
            public void handleMessage(Message msg) {  
                Log.i(TAG, "handleMessage");  
                switch (msg.what) {  
                case MessengerService.MSG_SET_VALUE:  
                    mCallbackText.setText("Received from service: " + msg.arg1);  
                    break;  
                default:  
                    super.handleMessage(msg);  
                }  
            }  
        };  
  
        /** 
         * 自己的信使 
         */  
        private Messenger mMessenger;  
          
        /** 
         * 远程服务的信使 
         */  
        private Messenger rMessenger;  
          
        private ServiceConnection connection = new ServiceConnection() {  
  
            public void onServiceConnected(ComponentName name, IBinder service) {  
                // TODO Auto-generated method stub  
                Log.i(TAG, "onServiceConnected");  
                rMessenger = new Messenger(service);  
                mMessenger = new Messenger(mHandler);  
                  
                sendMessage();  
            }  
  
  
            public void onServiceDisconnected(ComponentName name) {  
                // TODO Auto-generated method stub  
                rMessenger = null;  
            }  
        };  
  
        public void onClick(View v) {  
            // TODO Auto-generated method stub  
            Intent intent = new Intent(  
                    "com.xwangly.apidemo.app.messenger_service");  
            switch (v.getId()) {  
            case R.id.bind:  
                if (!isBound) {  
                    isBound = bindService(intent, connection, BIND_AUTO_CREATE);  
                    //isBound = true;  
                }else {  
                    sendMessage();  
                }  
                break;  
            case R.id.unbind:  
                if (isBound) {  
                    unbindService(connection);  
                    isBound = false;  
                }  
                break;  
            default:  
                break;  
            }  
        }  
          
        /** 
         * 使用服务端的信使向它发送一个消息。 
         */  
        private void sendMessage() {  
            // TODO Auto-generated method stub  
            Message message = Message.obtain(null, MessengerService.MSG_SET_VALUE);  
            message.replyTo = mMessenger;  
            try {  
                rMessenger.send(message);  
            } catch (RemoteException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
        }  
  
    }  
  
} 

AndroidManifest.xml相关配置如下：

<service android:name=".app.MessengerService" >
    <intent-filter>
        <action android:name="com.xwangly.apidemo.app.messenger_service" />
    </intent-filter>
</service>
      <activity android:name=".app.MessengerServiceActivities$Binding"
              android:label="@string/activity_messenger_service_binding"
              android:launchMode="singleTop">
          <intent-filter>
              <action android:name="android.intent.action.MAIN" />
              <category android:name="android.intent.category.LAUNCHER" />
          </intent-filter>
      </activity>

  
<service android:name=".app.MessengerService" >  
    <intent-filter>  
        <action android:name="com.xwangly.apidemo.app.messenger_service" />  
    </intent-filter>  
</service>  
      <activity android:name=".app.MessengerServiceActivities$Binding"  
              android:label="@string/activity_messenger_service_binding"  
              android:launchMode="singleTop">  
          <intent-filter>  
              <action android:name="android.intent.action.MAIN" />  
              <category android:name="android.intent.category.LAUNCHER" />  
          </intent-filter>  
      </activity>  

至于layout就不帖了，两个按钮一个文本域。