Android多进程系列
Messenger也可以作为Android多进程的一种通信方式，通过构建Message来在客户端和服务端之间传递数据
简单使用Messenger
客户端通过Messenger向服务端进程发送消息
public class MessengerService extends Service {
private static final String TAG = "MessagerService";
/**
* 处理来自客户端的消息，并用于构建Messenger
*/
private static class MessengerHandler extends Handler {
@Override
public void handleMessage(Message message) {
switch (message.what) {
case MESSAGE_FROM_CLIENT:
Log.e(TAG, "receive message from client:" + message.getData().getString("msg"));
break;
default:
super.handleMessage(message);
break;
}
}
}
/**
* 构建Messenger对象
*/
private final Messenger mMessenger = new Messenger(new MessengerHandler());
@Nullable
@Override
public IBinder onBind(Intent intent) {
//将Messenger对象的Binder返回给客户端
return mMessenger.getBinder();
}
}
<service
android:name="com.xxq2dream.service.MessengerService"
android:process=":remote" />
- 然后客户端是通过绑定服务端返回的binder来创建Messenger对象，并通过这个Messenger对象来向服务端发送消息
public class MessengerActivity extends AppCompatActivity {
private static final String TAG = "MessengerActivity";
private Messenger mService;
private ServiceConnection mConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
Log.e(TAG, "ServiceConnection-->" + System.currentTimeMillis());
//通过服务端返回的Binder创建Messenger
mService = new Messenger(iBinder);
//创建消息，通过Bundle传递数据
Message message = Message.obtain(null, MESSAGE_FROM_CLIENT);
Bundle bundle = new Bundle();
bundle.putString("msg", "hello service,this is client");
message.setData(bundle);
try {
//向服务端发送消息
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
Log.e(TAG, "onServiceDisconnected-->binder died");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_messenger);
//绑定服务
Intent intent = new Intent(this, MessengerService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
@Override
protected void onDestroy() {
//解绑服务
unbindService(mConnection);
super.onDestroy();
}
}
![服务端接收到客户端的消息]( "服务端接收到客户端的消息")
通过上面的额实践，我们可以看出利用Messenger进行跨进程通信，需要通过Message来传递消息，而Message可以通过setData方法利用Bundle来传递复杂的数据。
服务端如果要回复消息给客户端，那就要用到Message的replyTo参数了
private static class MessengerHandler extends Handler {
@Override
public void handleMessage(Message message) {
switch (message.what) {
case Constant.MESSAGE_FROM_CLIENT:
Log.e(TAG, "receive message from client:" + message.getData().getString("msg"));
//获取客户端传递过来的Messenger，通过这个Messenger回传消息给客户端
Messenger client = message.replyTo;
//当然，回传消息还是要通过message
Message msg = Message.obtain(null, Constant.MESSAGE_FROM_SERVICE);
Bundle bundle = new Bundle();
bundle.putString("msg", "hello client, I have received your message!");
msg.setData(bundle);
try {
client.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
break;
default:
super.handleMessage(message);
break;
}
}
}
- 客户端改造，主要是通过Handle构建一个Messenger对象，并在向服务端发送消息的时候，通过Message的replyTo参数将Messenger对象传递给服务端
/**
* 用于构建客户端的Messenger对象，并处理服务端的消息
*/
private static class MessengerHandler extends Handler {
@Override
public void handleMessage(Message message) {
switch (message.what) {
case Constant.MESSAGE_FROM_SERVICE:
Log.e(TAG, "receive message from service:" + message.getData().getString("msg"));
break;
default:
super.handleMessage(message);
break;
}
}
}
/**
* 客户端Messenger对象
*/
private Messenger mClientMessenger = new Messenger(new MessengerHandler());
private ServiceConnection mConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
Log.e(TAG, "ServiceConnection-->" + System.currentTimeMillis());
mService = new Messenger(iBinder);
Message message = Message.obtain(null, MESSAGE_FROM_CLIENT);
Bundle bundle = new Bundle();
bundle.putString("msg", "hello service,this is client");
message.setData(bundle);
//将客户端的Messenger对象传递给服务端
message.replyTo = mClientMessenger;
try {
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
Log.e(TAG, "onServiceDisconnected-->binder died");
}
};
![客户端收到服务端的消息回复]( "客户端收到服务端的消息回复")
总结
- 使用Messager来传递Message，Message中能使用的字段只有what、arg1、arg2、Bundle和replyTo,自定义的Parcelable对象无法通过object字段来传输
- Message中的Bundle支持多种数据类型，replyTo字段用于传输Messager对象，以便进程间相互通信
- Messager以串行的方式处理客户端发来的消息，不适合有大量并发的请求
- Messager方法只能传递消息，不能跨进程调用方法
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![AntDream]( "AntDream")
