Android11_IPC方式之Messenger

通过Messenger可以在不同的进程中传递Messenger对象；

Message放入我们需要传递的数据；就可以轻松实现数据的进程间传递；

Messenger是轻量级的IPC方案；底层实现是AIDL；

Messenger对AIDL做了封装，使得我们可以简便地进行进程间通信；

由于其一次处理一个请求，因此在服务端不需要考虑线程同步的问题；

因为服务端中不存在并发执行的情形；

1、服务端

创建一个Service来处理客户端的连接请求，同时创建一个Handler并通过它来创建一个Messenger对象；

然后在Service的onBind方法中返回这个Messenger对象底层的Binder即可；

2、客户端

首先要绑定服务端Service，绑定成功后用服务端返回的IBinder对象创建一个Messenger，通过这个Messenger对象就可向服务端发送消息了；

发消息的类型是Message对象，如果需要服务端能够回应客户端，那么也需要创建一个Handler并创建一个新的Messenger，

并把这个Messenger对象通过Message的replyTo参数传递给服务端；服务端通过这个replyTo参数就可以回应客户端。

===================================================

服务端代码：

package com.example.messengertest_server;

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 static final String TAG = "Service";
    private static final int MSG_OPCODE_1 = 1;

    //定义一个继承自Handler的类
    private static class MsgHandler extends  Handler {
        @Override
        public void handleMessage(Message msg){
            super.handleMessage(msg);
            switch(msg.what){
                case MSG_OPCODE_1:
                    //取出客户端的内容
                    Bundle bundle = msg.getData();  //取出bundle
                    String clientmsgstr = bundle.getString("client");  //解析bundle
                    Log.d(TAG,"Service handle msg with client string:"+clientmsgstr); //打印

                    //新建一个Message,回复客户端
                     Message replymsg = Message.obtain();  //创建消息
                     replymsg.what = MSG_OPCODE_1;
                     Bundle replybundle = new Bundle(); //创建bundle
                     replybundle.putString("service","我很好");//往bundle中存放数据
                     replymsg.setData(replybundle);//往消息中存放bundle

                    //对收到的msg进行回复
                     try{
                         msg.replyTo.send(replymsg); //msg.replyTo是客户端携带过来的Messenger对象
                     }catch(RemoteException e){
                         e.printStackTrace();
                     }
                     break;
                default:
                    break;
            }
        }
    }

    private MsgHandler mHandler = new MsgHandler();
    private Messenger mMessenger = new Messenger(mHandler);//创建一个Messenger，将Handler作为参数


    @Override
    public IBinder onBind(Intent intent){
        return mMessenger.getBinder();
    }

    @Override
    public void onCreate(){
        super.onCreate();
        Log.d(TAG, "onCreate: ");
        if(mMessenger == null){
            mMessenger = new Messenger(mHandler);
        }
    }

    @Override
    public void onDestroy(){
        super.onDestroy();
    }

}

===================================================

客户端代码：

package com.example.messengertest_client;

import androidx.appcompat.app.AppCompatActivity;
import android.content.ComponentName;
import android.content.Context;
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;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private static final String TAG = "Client";
    private static final int MSG_OPCODE_1 = 1;

    private boolean connected;  //用一个变量记录是否连接

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.btn_connect).setOnClickListener(this);
        findViewById(R.id.btn_unconnect).setOnClickListener(this);
    }

    @Override
    protected void onDestroy(){
        super.onDestroy();
        if(connected){
            unbindService(mConnection);
        }

    }

    //处理点击操作
    public void onClick(View view){
        switch (view.getId()){
            case R.id.btn_connect:
                Log.d(TAG,"Click btn_connect");
                Intent intent = new Intent();
                intent.setPackage("com.example.messengertest_server");
                intent.setAction("com.example.messengertest_server.MSGSERVICE");
                bindService(intent,mConnection, Context.BIND_AUTO_CREATE);
                break;
            case R.id.btn_unconnect:
                Log.d(TAG,"Click btn_unconnect");
                unbindService(mConnection);
                break;
            default:
                break;
        }
    }

    //ServiceConnection中的函数会被回调
    private ServiceConnection mConnection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {
            Log.d(TAG,"onServiceConnected Enter");
            connected = true;
            //建立连接后，给服务端发消息
            Messenger sendmessenger = new Messenger(service);

            Message sendmessage = Message.obtain();
            Bundle bundle = new Bundle();
            bundle.putString("client", "你好吗？");
            sendmessage.setData(bundle);
            sendmessage.what = MSG_OPCODE_1;
            sendmessage.replyTo = mMessenger;

            //利用messenger的send方法发送消息给服务端
            try{
                sendmessenger.send(sendmessage);
            }catch (RemoteException e){
               e.printStackTrace();
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            Log.d(TAG,"onServiceDisconnected Enter");
            connected = false;
        }
    };

    //定义一个继承自Handler的类
    private static class MsgHandler extends Handler {
        @Override
        public void handleMessage(Message msg){
            super.handleMessage(msg);
            Log.d(TAG,"Handle Message Enter");

            //处理来自服务端回复的消息
            if(MSG_OPCODE_1 == msg.what)
            {
                Bundle bundle = msg.getData();
                String replymsg = bundle.getString("service");
                Log.d(TAG,"Get service reply "+replymsg);
            }
        }
    }

    private MsgHandler mHandler = new MsgHandler();
    private Messenger mMessenger = new Messenger(mHandler);//创建一个Messenger，将Handler作为参数

}