Service与Activity的相互通信怎么在Android项目中实现

package com.example.communication; import android.app.Service; import android.content.Intent; import android.os.Binder; import android.os.IBinder;  public class MsgService extends Service {    public static final int MAX_PROGRESS = 100;    private int progress = 0;     public int getProgress() {   return progress;  }     public void startDownLoad(){   new Thread(new Runnable() {        @Override    public void run() {     while(progress < MAX_PROGRESS){      progress += 5;      try {       Thread.sleep(1000);      } catch (InterruptedException e) {       e.printStackTrace();      }           }    }   }).start();  }      @Override  public IBinder onBind(Intent intent) {   return new MsgBinder();  }    public class MsgBinder extends Binder{      public MsgService getService(){    return MsgService.this;   }  }  }