Android 通过Messager与Service实现进程间双向通信

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.ispring2.serviceapp" >

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="ServiceApp">

        <service
            android:name=".MyService"
            android:enabled="true"
            android:exported="true" >
            <intent-filter>
                <action android:name="com.ispring2.action.MYSERVICE" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </service>
    </application>

</manifest>

package com.ispring2.serviceapp;

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 MyService extends Service {

    private static final int RECEIVE_MESSAGE_CODE = 0x0001;

    private static final int SEND_MESSAGE_CODE = 0x0002;

    //clientMessenger表示的是客户端的Messenger，可以通过来自于客户端的Message的replyTo属性获得，
    //其内部指向了客户端的ClientHandler实例，可以用clientMessenger向客户端发送消息
    private Messenger clientMessenger = null;

    //serviceMessenger是Service自身的Messenger，其内部指向了ServiceHandler的实例
    //客户端可以通过IBinder构建Service端的Messenger，从而向Service发送消息，
    //并由ServiceHandler接收并处理来自于客户端的消息
    private Messenger serviceMessenger = new Messenger(new ServiceHandler());

    //MyService用ServiceHandler接收并处理来自于客户端的消息
    private class ServiceHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            Log.i("DemoLog", "ServiceHandler -> handleMessage");
            if(msg.what == RECEIVE_MESSAGE_CODE){
                Bundle data = msg.getData();
                if(data != null){
                    String str = data.getString("msg");
                    Log.i("DemoLog", "MyService收到客户端如下信息: " + str);
                }
                //通过Message的replyTo获取到客户端自身的Messenger，
                //Service可以通过它向客户端发送消息
                clientMessenger = msg.replyTo;
                if(clientMessenger != null){
                    Log.i("DemoLog", "MyService向客户端回信");
                    Message msgToClient = Message.obtain();
                    msgToClient.what = SEND_MESSAGE_CODE;
                    //可以通过Bundle发送跨进程的信息
                    Bundle bundle = new Bundle();
                    bundle.putString("msg", "你好，客户端，我是MyService");
                    msgToClient.setData(bundle);
                    try{
                        clientMessenger.send(msgToClient);
                    }catch (RemoteException e){
                        e.printStackTrace();
                        Log.e("DemoLog", "MyService向客户端发送信息失败: " + e.getMessage());
                    }
                }
            }
        }
    }

    @Override
    public void onCreate() {
        Log.i("DemoLog", "MyService -> onCreate");
        super.onCreate();
    }

    @Override
    public IBinder onBind(Intent intent) {
        Log.i("DemoLog", "MyServivce -> onBind");
        //获取Service自身Messenger所对应的IBinder，并将其发送共享给所有客户端
        return serviceMessenger.getBinder();
    }

    @Override
    public void onDestroy() {
        Log.i("DemoLog", "MyService -> onDestroy");
        clientMessenger = null;
        super.onDestroy();
    }
}

package com.ispring.clientapp;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
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.Button;


public class MainActivity extends Activity implements Button.OnClickListener {

    private static final int SEND_MESSAGE_CODE = 0x0001;

    private static final int RECEIVE_MESSAGE_CODE = 0x0002;

    private boolean isBound = false;

    //用于启动MyService的Intent对应的action
    private final String SERVICE_ACTION = "com.ispring2.action.MYSERVICE";

    //serviceMessenger表示的是Service端的Messenger，其内部指向了MyService的ServiceHandler实例
    //可以用serviceMessenger向MyService发送消息
    private Messenger serviceMessenger = null;

    //clientMessenger是客户端自身的Messenger，内部指向了ClientHandler的实例
    //MyService可以通过Message的replyTo得到clientMessenger，从而MyService可以向客户端发送消息，
    //并由ClientHandler接收并处理来自于Service的消息
    private Messenger clientMessenger = new Messenger(new ClientHandler());

    //客户端用ClientHandler接收并处理来自于Service的消息
    private class ClientHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            Log.i("DemoLog", "ClientHandler -> handleMessage");
            if(msg.what == RECEIVE_MESSAGE_CODE){
                Bundle data = msg.getData();
                if(data != null){
                    String str = data.getString("msg");
                    Log.i("DemoLog", "客户端收到Service的消息: " + str);
                }
            }
        }
    }

    private ServiceConnection conn = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder binder) {
            //客户端与Service建立连接
            Log.i("DemoLog", "客户端 onServiceConnected");

            //我们可以通过从Service的onBind方法中返回的IBinder初始化一个指向Service端的Messenger
            serviceMessenger = new Messenger(binder);
            isBound = true;

            Message msg = Message.obtain();
            msg.what = SEND_MESSAGE_CODE;

            //此处跨进程Message通信不能将msg.obj设置为non-Parcelable的对象，应该使用Bundle
            //msg.obj = "你好，MyService，我是客户端";
            Bundle data = new Bundle();
            data.putString("msg", "你好，MyService，我是客户端");
            msg.setData(data);

            //需要将Message的replyTo设置为客户端的clientMessenger，
            //以便Service可以通过它向客户端发送消息
            msg.replyTo = clientMessenger;
            try {
                Log.i("DemoLog", "客户端向service发送信息");
                serviceMessenger.send(msg);
            } catch (RemoteException e) {
                e.printStackTrace();
                Log.i("DemoLog", "客户端向service发送消息失败: " + e.getMessage());
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            //客户端与Service失去连接
            serviceMessenger = null;
            isBound = false;
            Log.i("DemoLog", "客户端 onServiceDisconnected");
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public void onClick(View v) {
        if(v.getId() == R.id.btnBindService){
            //单击了bindService按钮
            if(!isBound){
                Intent intent = new Intent();
                intent.setAction(SERVICE_ACTION);
                intent.addCategory(Intent.CATEGORY_DEFAULT);

                PackageManager pm = getPackageManager();
                //我们先通过一个隐式的Intent获取可能会被启动的Service的信息
                ResolveInfo info = pm.resolveService(intent, 0);

                if(info != null){
                    //如果ResolveInfo不为空，说明我们能通过上面隐式的Intent找到对应的Service
                    //我们可以获取将要启动的Service的package信息以及类型
                    String packageName = info.serviceInfo.packageName;
                    String serviceNmae = info.serviceInfo.name;
                    //然后我们需要将根据得到的Service的包名和类名，构建一个ComponentName
                    //从而设置intent要启动的具体的组件信息，这样intent就从隐式变成了一个显式的intent
                    //之所以大费周折将其从隐式转换为显式intent，是因为从Android 5.0 Lollipop开始，
                    //Android不再支持通过通过隐式的intent启动Service，只能通过显式intent的方式启动Service
                    //在Android 5.0 Lollipop之前的版本倒是可以通过隐式intent启动Service
                    ComponentName componentName = new ComponentName(packageName, serviceNmae);
                    intent.setComponent(componentName);
                    try{
                        Log.i("DemoLog", "客户端调用bindService方法");
                        bindService(intent, conn, BIND_AUTO_CREATE);
                    }catch(Exception e){
                        e.printStackTrace();
                        Log.e("DemoLog", e.getMessage());
                    }
                }
            }
        }else if(v.getId() == R.id.btnUnbindService){
            //单击了unbindService按钮
            if(isBound){
                Log.i("DemoLog", "客户端调用unbindService方法");
                unbindService(conn);
            }
        }
    }
}