Messenger:使用消息的跨进程通信

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

这篇文章题目其实做好叫：Activity和Service通过Messenger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

Java代码 

1. 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

Java代码 

1. 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）

Java代码 

1. public void onServiceConnected(ComponentName name, IBinder service) { 
2.     rMessenger = new Messenger(service); 
3. 　　　　　...... 
4. } 

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

Java代码 

1. /**
2. * Create a Messenger from a raw IBinder, which had previously been
3. * retrieved with {@link #getBinder}.
4. *
5. * @param target The IBinder this Messenger should communicate with.
6. */ 
7. public Messenger(IBinder target) { 
8.     mTarget = IMessenger.Stub.asInterface(target); 
9. } 

    /**     * 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);

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

Java代码 

1. //得到客户端的信使对象，并向它发送消息 
2. cMessenger = msg.replyTo; 
3. 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

Java代码 

1. package com.xwangly.apidemo.app; 
2.  
3. import java.util.Random; 
4.  
5. import android.app.Service; 
6. import android.content.Intent; 
7. import android.os.Handler; 
8. import android.os.IBinder; 
9. import android.os.Message; 
10. import android.os.Messenger; 
11. import android.os.RemoteException; 
12. import android.util.Log; 
13.  
14. public class MessengerServiceextends Service { 
15.     private String TAG = "MessengerService"; 
16.  
17.     @Override 
18.     public void onDestroy() { 
19.         // TODO Auto-generated method stub 
20.         Log.i(TAG, "onDestroy"); 
21.         cMessenger = null; 
22.         super.onDestroy(); 
23.     } 
24.  
25.     @Override 
26.     public boolean onUnbind(Intent intent) { 
27.         // TODO Auto-generated method stub 
28.         Log.i(TAG, "onUnbind"); 
29.         return super.onUnbind(intent); 
30.     } 
31.  
32.     static finalint MSG_REGISTER_CLIENT = 1; 
33.     static finalint MSG_UNREGISTER_CLIENT = 2; 
34.     static finalint MSG_SET_VALUE = 3; 
35.  
36.     private Random random = new Random(); 
37.  
38.     private Handler mHandler = new Handler() { 
39.  
40.         @Override 
41.         public void handleMessage(Message msg) { 
42.             // TODO Auto-generated method stub 
43.             Log.i(TAG, "handleMessage"); 
44.             switch (msg.what) { 
45.             case MSG_SET_VALUE: 
46.                 try { 
47.                     Message message = Message.obtain(null, 
48.                             MessengerService.MSG_SET_VALUE); 
49.                     message.arg1 = random.nextInt(100); 
50.                      
51.                     //得到客户端的信使对象，并向它发送消息 
52.                     cMessenger = msg.replyTo; 
53.                     cMessenger.send(message); 
54.                 } catch (RemoteException e) { 
55.                     // TODO Auto-generated catch block 
56.                     e.printStackTrace(); 
57.                 } 
58.                 break; 
59.             default: 
60.                 super.handleMessage(msg); 
61.             } 
62.  
63.         } 
64.     }; 
65.  
66.     /**
67.      * 自己的信使对象
68.      */ 
69.     private Messenger mMessenger = new Messenger(mHandler); 
70.  
71.     /**
72.      * 客户的信使
73.      */ 
74.     private Messenger cMessenger; 
75.  
76.     @Override 
77.     public IBinder onBind(Intent intent) { 
78.         // TODO Auto-generated method stub 
79.         Log.i(TAG, "onBind"); 
80.         //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)） 
81.         return mMessenger.getBinder(); 
82.     } 
83.  
84.     @Override 
85.     public void onRebind(Intent intent) { 
86.         // TODO Auto-generated method stub 
87.         Log.i(TAG, "onRebind"); 
88.  
89.     } 
90.  
91. } 

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";@Overridepublic void onDestroy() {// TODO Auto-generated method stubLog.i(TAG, "onDestroy");cMessenger = null;super.onDestroy();}@Overridepublic boolean onUnbind(Intent intent) {// TODO Auto-generated method stubLog.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() {@Overridepublic void handleMessage(Message msg) {// TODO Auto-generated method stubLog.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 blocke.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;@Overridepublic IBinder onBind(Intent intent) {// TODO Auto-generated method stubLog.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();}@Overridepublic void onRebind(Intent intent) {// TODO Auto-generated method stubLog.i(TAG, "onRebind");}}

MessengerServiceActivities.java

Java代码 

1. package com.xwangly.apidemo.app; 
2.  
3. import com.xwangly.apidemo.R; 
4.  
5. import android.app.Activity; 
6. import android.content.ComponentName; 
7. import android.content.Intent; 
8. import android.content.ServiceConnection; 
9. import android.os.Bundle; 
10. import android.os.Handler; 
11. import android.os.IBinder; 
12. import android.os.Message; 
13. import android.os.Messenger; 
14. import android.os.RemoteException; 
15. import android.util.Log; 
16. import android.view.View; 
17. import android.widget.TextView; 
18.  
19. public class MessengerServiceActivities { 
20.     public staticclass Binding extends Activityimplements 
21.             View.OnClickListener { 
22.         private String TAG = "Binding"; 
23.  
24.         TextView mCallbackText; 
25.  
26.         private boolean isBound; 
27.  
28.         @Override 
29.         protected void onCreate(Bundle savedInstanceState) { 
30.             // TODO Auto-generated method stub 
31.             super.onCreate(savedInstanceState); 
32.             setContentView(R.layout.messenger_service_binding); 
33.             findViewById(R.id.bind).setOnClickListener(this); 
34.             findViewById(R.id.unbind).setOnClickListener(this); 
35.  
36.             mCallbackText = (TextView) findViewById(R.id.callback); 
37.             mCallbackText.setText("Not attached."); 
38.  
39.         } 
40.  
41.         private Handler mHandler = new Handler() { 
42.             @Override 
43.             public void handleMessage(Message msg) { 
44.                 Log.i(TAG, "handleMessage"); 
45.                 switch (msg.what) { 
46.                 case MessengerService.MSG_SET_VALUE: 
47.                     mCallbackText.setText("Received from service: " + msg.arg1); 
48.                     break; 
49.                 default: 
50.                     super.handleMessage(msg); 
51.                 } 
52.             } 
53.         }; 
54.  
55.         /**
56.          * 自己的信使
57.          */ 
58.         private Messenger mMessenger; 
59.          
60.         /**
61.          * 远程服务的信使
62.          */ 
63.         private Messenger rMessenger; 
64.          
65.         private ServiceConnection connection =new ServiceConnection() { 
66.  
67.             public void onServiceConnected(ComponentName name, IBinder service) { 
68.                 // TODO Auto-generated method stub 
69.                 Log.i(TAG, "onServiceConnected"); 
70.                 rMessenger = new Messenger(service); 
71.                 mMessenger = new Messenger(mHandler); 
72.                  
73.                 sendMessage(); 
74.             } 
75.  
76.  
77.             public void onServiceDisconnected(ComponentName name) { 
78.                 // TODO Auto-generated method stub 
79.                 rMessenger = null; 
80.             } 
81.         }; 
82.  
83.         public void onClick(View v) { 
84.             // TODO Auto-generated method stub 
85.             Intent intent = new Intent( 
86.                     "com.xwangly.apidemo.app.messenger_service"); 
87.             switch (v.getId()) { 
88.             case R.id.bind: 
89.                 if (!isBound) { 
90.                     isBound = bindService(intent, connection, BIND_AUTO_CREATE); 
91.                     //isBound = true; 
92.                 }else { 
93.                     sendMessage(); 
94.                 } 
95.                 break; 
96.             case R.id.unbind: 
97.                 if (isBound) { 
98.                     unbindService(connection); 
99.                     isBound = false; 
100.                 } 
101.                 break; 
102.             default: 
103.                 break; 
104.             } 
105.         } 
106.          
107.         /**
108.          * 使用服务端的信使向它发送一个消息。
109.          */ 
110.         private void sendMessage() { 
111.             // TODO Auto-generated method stub 
112.             Message message = Message.obtain(null, MessengerService.MSG_SET_VALUE); 
113.             message.replyTo = mMessenger; 
114.             try { 
115.                 rMessenger.send(message); 
116.             } catch (RemoteException e) { 
117.                 // TODO Auto-generated catch block 
118.                 e.printStackTrace(); 
119.             } 
120.         } 
121.  
122.     } 
123.  
124. } 

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 implementsView.OnClickListener {private String TAG = "Binding";TextView mCallbackText;private boolean isBound;@Overrideprotected void onCreate(Bundle savedInstanceState) {// TODO Auto-generated method stubsuper.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() {@Overridepublic 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 stubLog.i(TAG, "onServiceConnected");rMessenger = new Messenger(service);mMessenger = new Messenger(mHandler);sendMessage();}public void onServiceDisconnected(ComponentName name) {// TODO Auto-generated method stubrMessenger = null;}};public void onClick(View v) {// TODO Auto-generated method stubIntent 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 stubMessage message = Message.obtain(null, MessengerService.MSG_SET_VALUE);message.replyTo = mMessenger;try {rMessenger.send(message);} catch (RemoteException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}

AndroidManifest.xml相关配置如下：

Xml代码 

1. <service android:name=".app.MessengerService"> 
2.     <intent-filter> 
3.         <actionandroid:name="com.xwangly.apidemo.app.messenger_service"/> 
4.     </intent-filter> 
5. </service> 
6.       <activityandroid:name=".app.MessengerServiceActivities$Binding" 
7.               android:label="@string/activity_messenger_service_binding" 
8.               android:launchMode="singleTop"> 
9.           <intent-filter> 
10.               <actionandroid:name="android.intent.action.MAIN"/> 
11.               <categoryandroid:name="android.intent.category.LAUNCHER"/> 
12.           </intent-filter> 
13.       </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>