<?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表示的是客戶端的Messenger，可以通過(guò)來(lái)自于客戶端的Message的replyTo屬性獲得，
    //其內(nèi)部指向了客戶端的ClientHandler實(shí)例，可以用clientMessenger向客戶端發(fā)送消息
    private Messenger clientMessenger = null;

    //serviceMessenger是Service自身的Messenger，其內(nèi)部指向了ServiceHandler的實(shí)例
    //客戶端可以通過(guò)IBinder構(gòu)建Service端的Messenger，從而向Service發(fā)送消息，
    //并由ServiceHandler接收并處理來(lái)自于客戶端的消息
    private Messenger serviceMessenger = new Messenger(new ServiceHandler());

    //MyService用ServiceHandler接收并處理來(lái)自于客戶端的消息
    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收到客戶端如下信息: " + str);
                }
                //通過(guò)Message的replyTo獲取到客戶端自身的Messenger，
                //Service可以通過(guò)它向客戶端發(fā)送消息
                clientMessenger = msg.replyTo;
                if(clientMessenger != null){
                    Log.i("DemoLog", "MyService向客戶端回信");
                    Message msgToClient = Message.obtain();
                    msgToClient.what = SEND_MESSAGE_CODE;
                    //可以通過(guò)Bundle發(fā)送跨進(jìn)程的信息
                    Bundle bundle = new Bundle();
                    bundle.putString("msg", "你好，客戶端，我是MyService");
                    msgToClient.setData(bundle);
                    try{
                        clientMessenger.send(msgToClient);
                    }catch (RemoteException e){
                        e.printStackTrace();
                        Log.e("DemoLog", "MyService向客戶端發(fā)送信息失敗: " + e.getMessage());
                    }
                }
            }
        }
    }

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

    @Override
    public IBinder onBind(Intent intent) {
        Log.i("DemoLog", "MyServivce -> onBind");
        //獲取Service自身Messenger所對(duì)應(yīng)的IBinder，并將其發(fā)送共享給所有客戶端
        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;

    //用于啟動(dòng)MyService的Intent對(duì)應(yīng)的action
    private final String SERVICE_ACTION = "com.ispring2.action.MYSERVICE";

    //serviceMessenger表示的是Service端的Messenger，其內(nèi)部指向了MyService的ServiceHandler實(shí)例
    //可以用serviceMessenger向MyService發(fā)送消息
    private Messenger serviceMessenger = null;

    //clientMessenger是客戶端自身的Messenger，內(nèi)部指向了ClientHandler的實(shí)例
    //MyService可以通過(guò)Message的replyTo得到clientMessenger，從而MyService可以向客戶端發(fā)送消息，
    //并由ClientHandler接收并處理來(lái)自于Service的消息
    private Messenger clientMessenger = new Messenger(new ClientHandler());

    //客戶端用ClientHandler接收并處理來(lái)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", "客戶端收到Service的消息: " + str);
                }
            }
        }
    }

    private ServiceConnection conn = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder binder) {
            //客戶端與Service建立連接
            Log.i("DemoLog", "客戶端 onServiceConnected");

            //我們可以通過(guò)從Service的onBind方法中返回的IBinder初始化一個(gè)指向Service端的Messenger
            serviceMessenger = new Messenger(binder);
            isBound = true;

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

            //此處跨進(jìn)程Message通信不能將msg.obj設(shè)置為non-Parcelable的對(duì)象，應(yīng)該使用Bundle
            //msg.obj = "你好，MyService，我是客戶端";
            Bundle data = new Bundle();
            data.putString("msg", "你好，MyService，我是客戶端");
            msg.setData(data);

            //需要將Message的replyTo設(shè)置為客戶端的clientMessenger，
            //以便Service可以通過(guò)它向客戶端發(fā)送消息
            msg.replyTo = clientMessenger;
            try {
                Log.i("DemoLog", "客戶端向service發(fā)送信息");
                serviceMessenger.send(msg);
            } catch (RemoteException e) {
                e.printStackTrace();
                Log.i("DemoLog", "客戶端向service發(fā)送消息失敗: " + e.getMessage());
            }
        }

        @Override
        public void onServiceDisconnected(ComponentName name) {
            //客戶端與Service失去連接
            serviceMessenger = null;
            isBound = false;
            Log.i("DemoLog", "客戶端 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){
            //單擊了bindService按鈕
            if(!isBound){
                Intent intent = new Intent();
                intent.setAction(SERVICE_ACTION);
                intent.addCategory(Intent.CATEGORY_DEFAULT);

                PackageManager pm = getPackageManager();
                //我們先通過(guò)一個(gè)隱式的Intent獲取可能會(huì)被啟動(dòng)的Service的信息
                ResolveInfo info = pm.resolveService(intent, 0);

                if(info != null){
                    //如果ResolveInfo不為空，說(shuō)明我們能通過(guò)上面隱式的Intent找到對(duì)應(yīng)的Service
                    //我們可以獲取將要啟動(dòng)的Service的package信息以及類型
                    String packageName = info.serviceInfo.packageName;
                    String serviceNmae = info.serviceInfo.name;
                    //然后我們需要將根據(jù)得到的Service的包名和類名，構(gòu)建一個(gè)ComponentName
                    //從而設(shè)置intent要啟動(dòng)的具體的組件信息，這樣intent就從隱式變成了一個(gè)顯式的intent
                    //之所以大費(fèi)周折將其從隱式轉(zhuǎn)換為顯式intent，是因?yàn)閺腁ndroid 5.0 Lollipop開(kāi)始，
                    //Android不再支持通過(guò)通過(guò)隱式的intent啟動(dòng)Service，只能通過(guò)顯式intent的方式啟動(dòng)Service
                    //在Android 5.0 Lollipop之前的版本倒是可以通過(guò)隱式intent啟動(dòng)Service
                    ComponentName componentName = new ComponentName(packageName, serviceNmae);
                    intent.setComponent(componentName);
                    try{
                        Log.i("DemoLog", "客戶端調(diào)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){
            //單擊了unbindService按鈕
            if(isBound){
                Log.i("DemoLog", "客戶端調(diào)用unbindService方法");
                unbindService(conn);
            }
        }
    }
}