活动和服务进行通信

        我们学习了启动和停止服务的方法，虽然服务是在活动里启动的，但在启动了服务之后，活动与服务基本上就没有什么关系了。确实如此，我们在活动里调用了StartCommand()方法来启动MyService这个服务，然后MyService的onCreate()和onStartCommand()方法就会得到执行。之后服务就一直处于运行状态，但具体运行的是什么逻辑，活动就控制不了了。这就类似于活动通知了服务一下：“你可以启动了！”然后服务就去忙自己的事情了，但活动并不知道服务到底去做了什么事情，以及完成的如何。

比如说，目前我们希望在MyService里提供一个下载功能，然后在活动中可以决定何时开始下载，以及随时查看下载进度。实现这个功能的思路是创建一个专门的Binder对象来对下载功能进行管理，修改MyService中的代码

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");
    }
}

修改布局文件

修改MainActivity文件内容

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);



            }
        });

    }


}