Activity与Service使用Messenger通信

参考：

http://xwangly.iteye.com/blog/1109424

Messenger介绍：

Reference to a Handler, which others can use to send messages to it. This allows for the implementation of message-based communication across processes, by creating a Messenger pointing to a Handler in one process, and handing that Messenger to another process.

大意为：它引用了一个Handler对象，以便others能够向它发送消息。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。

使用方法：

1.服务端创建一个Messenger对象

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

2.（客户端）Activity绑定服务  bindService，服务返回一个binder，return mMessenger.getBinder();

3. Activity利用返回的binder，创建一个信使rMessenger = new Messenger(service);

4. Activity可以利用rMessenger向服务发送消息，rMessenger.send(msg),可以在msg中设置msg.replyTo = mMessenger(Activity的自身的信使）;这样服务端也能得到客户端的Messenger，可利用这个Messenger向客户端发送消息。

例子如下：

   客户端(MainActivity)向服务（MessengerService）发送查询时间的请求，服务端查询时间后，将时间返回给客户端。

//MainActivity

package com.example.servmessage;
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.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity{
        private String TAG = "Binding";
        private Button bindButton,unbindButton,sendmsgButton;
        private TextView msgText;
        private boolean isBound;
        private Messenger mMessenger;//自己的信使
        private Messenger rMessenger; //远程服务的信使
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            // TODO Auto-generated method stub
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            bindButton=(Button)findViewById(R.id.bind);
            unbindButton=(Button)findViewById(R.id.unbind);
            sendmsgButton=(Button)findViewById(R.id.msg);
            msgText = (TextView) findViewById(R.id.callback);
            msgText.setText("未绑定.");
            //绑定
            bindButton.setOnClickListener(new OnClickListener() {
                
                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    if (!isBound) {
                        Intent intent = new Intent(MainActivity.this,MessengerService.class);
                        startService(intent);
                        isBound = bindService(intent, connection, BIND_AUTO_CREATE);
                        msgText.setText("绑定成功");
                    }
                }
            });
            //解绑定
            unbindButton.setOnClickListener(new OnClickListener() {
                
                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    if (isBound) {
                        unbindService(connection);
                        isBound = false;
                        msgText.setText("已解除绑定");
                    }
                }
            });
            //发送查询消息
            sendmsgButton.setOnClickListener(new OnClickListener() {
                
                @Override
                public void onClick(View v) {
                    // TODO Auto-generated method stub
                    if(isBound)
                        sendMessage();
                }
            });

        }
        private Handler mHandler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                Log.i(TAG, "handleMessage");
                switch (msg.what) {
                case MessengerService.MSG_SET_TIME:
                    Bundle data=msg.getData();
                    String time=data.getString("time");
                    msgText.setText("current time: " +time);
                    break;
                default:
                    super.handleMessage(msg);
                }
            }
        };
        
        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);            
            }
            public void onServiceDisconnected(ComponentName name) {
                // TODO Auto-generated method stub
                rMessenger = null;
            }
        };    
         // 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_TIME);
            message.replyTo = mMessenger;
            try {
                rMessenger.send(message);
            } catch (RemoteException e) {
                e.printStackTrace();
            }
        }

    }

//MessengerService

package com.example.servmessage;


import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Random;

import android.app.Service;
import android.content.Intent;
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;

public class MessengerService extends Service {
    private String TAG = "MessengerService";
    private String DEFAULT_TIME_FORMAT = "yyyy-MM-dd hh:mm:ss";
    static final int MSG_SET_TIME = 1;
    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_TIME:
                try {
                    Message message = Message.obtain(null,
                            MessengerService.MSG_SET_TIME);                    
                    SimpleDateFormat dateFormatter = new SimpleDateFormat(DEFAULT_TIME_FORMAT);  
                   String time = dateFormatter.format(Calendar.getInstance().getTime());  
                   Bundle data=new Bundle();
                   data.putString("time", time);
                   message.setData(data);                    
                    //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);
            }

        }
    };
    private Messenger mMessenger = new Messenger(mHandler);// 自己的信使对象
    private Messenger cMessenger;//客户的信使

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

    }

}

//布局文件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
   >

    <TextView
        android:id="@+id/callback"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginTop="60dp"
        android:text="TextView" />

    <Button
        android:id="@+id/unbind"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/callback"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="152dp"
        android:text="解除绑定" />

    <Button
        android:id="@+id/bind"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/unbind"
        android:layout_alignBottom="@+id/unbind"
        android:layout_toLeftOf="@+id/unbind"
        android:text="绑定" />

    <Button
        android:id="@+id/msg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/unbind"
        android:layout_alignBottom="@+id/unbind"
        android:layout_toRightOf="@+id/unbind"
        android:text="发送消息" />
   
    </RelativeLayout>