我們學習了啟動和停止服務的方法，雖然服務是在活動裡啟動的，但在啟動了服務之後，活動與服務基本上就沒有什麼關係了。確實如此，我們在活動裡呼叫了StartCommand()方法來啟動MyService這個服務，然後MyService的onCreate()和onStartCommand()方法就會得到執行。之後服務就一直處於執行狀態，但具體執行的是什麼邏輯，活動就控制不了了。這就類似於活動通知了服務一下：“你可以啟動了！”然後服務就去忙自己的事情了，但活動並不知道服務到底去做了什麼事情，以及完成的如何。

比如說，目前我們希望在MyService裡提供一個下載功能，然後在活動中可以決定何時開始下載，以及隨時檢視下載進度。實現這個功能的思路是建立一個專門的Binder物件來對下載功能進行管理，修改MyService中的程式碼

package com.example.yxp.service;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;

public class MyService extends Service {
    private DownloadBinder mBinder = new DownloadBinder();
    class DownloadBinder extends Binder {
        public void startDownload(){
            Log.d("MyService","startDownload executed");
        }
        public int getProgress(){
            Log.d("MyService","getProgress executed");
            return 0;
        }
    }
    public IBinder onBind(Intent intent){
        return mBinder;
    }
    public MyService() {
    }

    public void onCreate(){
        super.onCreate();
        Log.d("MyService","onCreate executed");
    }

    public int onStartCommand(Intent intent,int flags,int startId){
        Log.d("MyService","onStartCommand executed");
        return super.onStartCommand(intent,flags,startId);
    }

    public void onDestroy(){
        super.onDestroy();
        Log.d("MyService", "onDestroy executed");
    }
}
 

修改佈局檔案

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">





    <Button
        android:id="@+id/start_service"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Start Service"/>
    <Button
        android:id="@+id/stop_service"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Stop Service"/>
    <Button
        android:id="@+id/bind_service"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Bind Service"/>
    <Button
        android:id="@+id/unbind_service"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Unbind Service"/>


</LinearLayout>
 

修改MainActivity檔案內容

package com.example.yxp.service;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;

import java.sql.BatchUpdateException;

public class MainActivity extends Activity {
    private MyService.DownloadBinder downloadBinder;
    private ServiceConnection connection = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {

            downloadBinder = (MyService.DownloadBinder) service;
            downloadBinder.startDownload();
            downloadBinder.getProgress();

        }


        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };


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

        final Button startService = (Button) findViewById(R.id.start_service);
        Button stopService  = (Button) findViewById(R.id.stop_service);

        startService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent startIntent = new Intent(MainActivity.this,MyService.class);
                startService(startIntent);

            }
        });

        stopService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent stopIntent = new Intent(MainActivity.this,MyService.class);
                stopService(stopIntent);

            }
        });

        final Button bindService = (Button) findViewById(R.id.bind_service);
        final Button unbindService = (Button) findViewById(R.id.unbind_service);
        bindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            Intent bindIntent = new Intent(MainActivity.this,MyService.class);
            bindService(bindIntent,connection,BIND_AUTO_CREATE);


            }
        });
        unbindService.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
            unbindService(connection);



            }
        });

    }


}