android Messenger 跨进程通信

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







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







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







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

Java代码







/**
* 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);

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







//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

Java代码







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

Java代码







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：

Xml代码







<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。