用Messager进行IPC

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。

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 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();
            }
        }

    }

}

        <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>