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Messenger:使用消息的跨進程通信

Messenger:信使

官方文檔解釋：它引用了一個Handler對象，以便others能夠向它發送消息(使用mMessenger.send(Message msg)方法)。該類允許跨進程間基於Message的通信(即兩個進程間可以通過Message進行通信)，在服務端使用Handler創建一個Messenger，客戶端持有這個Messenger就可以與服務端通信了。

以前我們使用Handler+Message的方式進行通信，都是在同一個進程中，從線程持有一個主線程的Handler對象，並向主線程發送消息。

而Android既然可以使用bindler機製進行跨進行通信，所以我們當然可以將Handler與bindler結合起來進行跨進程發送消息。

查看API就可以發現，Messenger就是這種方式的實現。

一般使用方法如下：

１。遠程通過

Java代碼

1. mMessenger = new Messenger(mHandler)

mMessenger = new Messenger(mHandler)

創建一個信使對象

２。客戶端使用bindlerService請求連接遠程

３。遠程onBind方法返回一個bindler

Java代碼

1. return mMessenger.getBinder();

return mMessenger.getBinder();

4.客戶端使用遠程返回的bindler得到一個信使（即得到遠程信使）

Java代碼

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);
　　　　　　　　......
			}

這裏雖然是new了一個Messenger，但我們查看它的實現

Java代碼

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);
    }

發現它的mTarget是通過Aidl得到的，實際上就是遠程創建的那個。

５。客戶端可以使用這個遠程信使對象向遠程發送消息：rMessenger.send(msg);

這樣遠程服務端的Handler對象就能收到消息了，然後可以在其handlerMessage(Message msg)方法中進行處理。（該Handler對象就是第一步服務端創建Messenger時使用的參數mHandler）.

經過這５個步驟貌似隻有客戶端向服務端發送消息，這樣的消息傳遞是單向的，那麼如何實現雙向傳遞呢？

首先需要在第５步稍加修改，在send(msg)前通過msm.replyTo = mMessenger將自己的信使設置到消息中，這樣服務端接收到消息時同時也得到了客戶端的信使對象了，然後服務端可以通過

Java代碼

1. //得到客戶端的信使對象，並向它發送消息
2. cMessenger = msg.replyTo;
3. cMessenger.send(message);

//得到客戶端的信使對象，並向它發送消息
cMessenger = msg.replyTo;
cMessenger.send(message);

即完成了從服務端向客戶端發送消息的功能，這樣客服端可以在自己的Handler對象的handlerMessage方法中接收服務端發送來的message進行處理。

雙向通信宣告完成。

下麵改寫ApiDemos工程實現Messenger通信

MessengerService.java

Java代碼

1. package com.xwangly.apidemo.app;
3. import java.util.Random;
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;
14. public class MessengerService extends Service {
15. private String TAG = "MessengerService";
17. @Override
18. public void onDestroy() {
19. // TODO Auto-generated method stub
20. Log.i(TAG, "onDestroy");
21. cMessenger = null;
22. super.onDestroy();
23. }
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. }
32. static final int MSG_REGISTER_CLIENT = 1;
33. static final int MSG_UNREGISTER_CLIENT = 2;
34. static final int MSG_SET_VALUE = 3;
36. private Random random = new Random();
38. private Handler mHandler = new Handler() {
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);
51. //得到客戶端的信使對象，並向它發送消息
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. }
63. }
64. };
66. /**
67. * 自己的信使對象
68. */
69. private Messenger mMessenger = new Messenger(mHandler);
71. /**
72. * 客戶的信使
73. */
74. private Messenger cMessenger;
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,以供客戶端通過這個bindler得到服務端的信使對象（通過new Messenger(bindler)）
81. return mMessenger.getBinder();
82. }
84. @Override
85. public void onRebind(Intent intent) {
86. // TODO Auto-generated method stub
87. Log.i(TAG, "onRebind");
89. }
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";

	@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);
					
					//得到客戶端的信使對象，並向它發送消息
					cMessenger = msg.replyTo;
					cMessenger.send(message);
				} catch (RemoteException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				break;
			default:
				super.handleMessage(msg);
			}

		}
	};

	/**
	 * 自己的信使對象
	 */
	private Messenger mMessenger = new Messenger(mHandler);

	/**
	 * 客戶的信使
	 */
	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,以供客戶端通過這個bindler得到服務端的信使對象（通過new Messenger(bindler)）
		return mMessenger.getBinder();
	}

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

	}

}

MessengerServiceActivities.java

Java代碼

1. package com.xwangly.apidemo.app;
3. import com.xwangly.apidemo.R;
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;
19. public class MessengerServiceActivities {
20. public static class Binding extends Activity implements
21. View.OnClickListener {
22. private String TAG = "Binding";
24. TextView mCallbackText;
26. private boolean isBound;
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);
36. mCallbackText = (TextView) findViewById(R.id.callback);
37. mCallbackText.setText("Not attached.");
39. }
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. };
55. /**
56. * 自己的信使
57. */
58. private Messenger mMessenger;
60. /**
61. * 遠程服務的信使
62. */
63. private Messenger rMessenger;
65. private ServiceConnection connection = new ServiceConnection() {
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);
73. sendMessage();
74. }
77. public void onServiceDisconnected(ComponentName name) {
78. // TODO Auto-generated method stub
79. rMessenger = null;
80. }
81. };
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. }
107. /**
108. * 使用服務端的信使向它發送一個消息。
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. }
122. }
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 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;
		
		/**
		 * 遠程服務的信使
		 */
		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;
			}
		}
		
		/**
		 * 使用服務端的信使向它發送一個消息。
		 */
		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相關配置如下：

Xml代碼

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

至於layout就不帖了，兩個按鈕一個文本域。

最後更新：2017-04-02 06:52:22

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