Android中信息交互大致有两种方式:

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1. 使用intent在service和activity之间不停地传递信息

2. 使用bindService实现, 这里有两种实现方式, 在重写service当中的onBind方法是,一种方式是通过实现一个Binder接口, 通过在这个接口中的实现一个getService方法返回service.this实现,另一种方法是使用aidl这种接口来实现.

现在截取部分代码:

第一种实现方式

Service中代码

class MBinder extends Binder {
  MyService getService(){

   returnMyService.this;
  }
}
//切记此处需要进行初始化
private MBinder mBinder = new MBinder();

第二种实现方式

Service中代码:

  public int playMusic()throws android.os.RemoteException {
           Log.i("CHEN","Play music");
           //创建音乐播放器
           if(mp == null) {
            mp = MediaPlayer.create(MyService.this,R.raw.today);
            mp.stop();
            try {
     mp.prepare();
    }catch (IllegalStateException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }catch (IOException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }
            mp.start();
            isStart = true;
            return CREATE;
           } else if(!isStart) {
            mp.stop();
            try {
     mp.prepare();
    }catch (IllegalStateException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }catch (IOException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }
            mp.start();
            isStart = true;
            return START;
           } else if(mp.isPlaying()) {
            mp.pause();
            return PAUSE;
           } else {
            mp.start();
            return PLAY;
           }

  }

.aidl接口定义

//切记此处需要指明包名

package android.mp3player;
interface MusicControlService
{

int playMusic();
void stopMusic();
int getCondition();
}

在解决了信息交互的问题后, 仍存在一个容易忽视的问题,你的Service如何被多次创建的activity取得而不是在创建新的service,也就是说怎么样实现在一个activity被关闭后再次打开仍能够取得你之前创建的service.

这里有一个小技巧.

通过为activity和service中主要方法(onCreate, onStart, bindService,unBindService, reBind等添加log.v()的日志输出命令) 我们可以观察到整个程序的执行顺序:

activityCreate, activityStart, bindService, serviceCreate,serviceStart, activityUnBind, activityStop, activityDestroy.

这个周期中我没有调用startService方法, 而是只是用了bindService方法,它自动调用了service的Create, Start方法, 也就是说这样会再次创建一个Service.

想要取得之前创建的Service, 达到创建一次, 使用多次的目的, 需要直接调用startActivity方法,同时重写Service中unbind方法和rebind方法.这次当activity调用startService方法的时候会自动判断是否存在以创建的Service,然后调用rebind方法取得这个对象.

粘贴代码如下

Service中

package android.mp3player;

import java.io.IOException;

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

public class MyService extends Service {

public static final int CREATE = 0;
public static final int START = 1;
public static final int PAUSE = 2;
public static final int PLAY = 3;
public static final int STOP = 4;
public static final int UNCREATE = 5;

private final MusicControlService.Stub binder =new MusicControlService.Stub()
{
       MediaPlayer mp;
  boolean isStart;

  public int playMusic() throwsandroid.os.RemoteException {
           Log.i("CHEN","Play music");
           //创建音乐播放器
           if(mp == null) {
            mp = MediaPlayer.create(MyService.this,R.raw.today);
            mp.stop();
            try {
     mp.prepare();
    }catch (IllegalStateException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }catch (IOException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }
            mp.start();
            isStart = true;
            return CREATE;
           } else if(!isStart) {
            mp.stop();
            try {
     mp.prepare();
    }catch (IllegalStateException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }catch (IOException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }
            mp.start();
            isStart = true;
            return START;
           } else if(mp.isPlaying()) {
            mp.pause();
            return PAUSE;
           } else {
            mp.start();
            return PLAY;
           }

  }

  public void stopMusic()throws android.os.RemoteException {
           Log.i("CHEN", "Stop music");
           if(mp.isPlaying()) {
            isStart = false;
            mp.stop();
           }
  }

  public int getCondition()throws android.os.RemoteException {
   if(mp ==null)
    returnUNCREATE;
   elseif(!isStart)
    returnSTOP;
   elseif(!mp.isPlaying())
    returnPAUSE;
   else
    returnPLAY;
  }
};

@Override
public IBinder onBind(Intent arg0) {
  // TODO Auto-generated methodstub
  Log.v("MyService","Bind");
  return binder;
}

@Override
public void onCreate() {
  // TODO Auto-generated methodstub
  super.onCreate();
  Log.v("MyService","Create");
}

@Override
public boolean onUnbind(Intent intent) {
  // TODO Auto-generated methodstub
  Log.v("MyService","Unbind");
  return true;
}

@Override
public void onRebind(Intent intent) {
  // TODO Auto-generated methodstub
  super.onRebind(intent);
  Log.v("MyService","Rebind");
}

}

Activity当中

package android.mp3player;

import java.io.IOException;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ImageButton;

public class Mp3Player extends Activity {
private Context mContext;
private ImageButton bt1;
private ImageButton bt2;
private Intent intent;
public MusicControlServicemusicControlService;
private ServiceConnection sc;

@Override
public void onCreate(Bundle savedInstanceState){
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);
  bt1 = (ImageButton)findViewById(R.id.iButton01);
  bt2 = (ImageButton)findViewById(R.id.iButton02);
  bt1.setBackgroundResource(R.drawable.ibtbg);
  bt2.setBackgroundResource(R.drawable.ibtbg);
  mContext = this;

  //将Mp3Player与MyService绑定
  intent = new Intent(mContext,MyService.class);
  sc = new ServiceConnection(){
   public voidonServiceConnected(ComponentName arg0, IBinder iBinder) {
    //TODO Auto-generated method stub
    musicControlService= MusicControlService.Stub.asInterface(iBinder);

//如果希望程序能够取得Service中的信息, 请将代码写在ServiceConnected方法中, 写在外部onCreate

    //或是onStart程序无法执行(参照之前我说的执行顺序)
    try{
     if(musicControlService.getCondition()== MyService.PLAY)
     {
      bt1.setImageResource(R.drawable.ibt3);
      Log.v("ServiceConnection","Pause Button replaced");
     }
     else{
      bt1.setImageResource(R.drawable.ibt1);
      Log.v("ServiceConnection","Play Button replaced");
     }
    }catch (RemoteException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
     Log.v("MusicControlService","fail init");
    }
   }

   publicvoid onServiceDisconnected(ComponentName arg0) {
    //TODO Auto-generated method stub
    musicControlService= null;
   }

  };
  bindService(intent, sc,BIND_AUTO_CREATE);
  startService(intent);
  Log.v("mp3player","Create");
}

@Override
protected void onStart() {
  // TODO Auto-generated methodstub
  super.onStart();

  bt1.setOnClickListener(newOnClickListener() {

   publicvoid onClick(View v) {
    //TODO Auto-generated method stub
    Log.v("Mp3playerbt1","Clicked");
    try{
     if(musicControlService.playMusic()== MyService.PAUSE) {
      bt1.setImageResource(R.drawable.ibt1);
     }else {
      bt1.setImageResource(R.drawable.ibt3);
     }
    }catch (RemoteException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }
   }

  });

bt2.setOnClickListener(newOnClickListener() {

   publicvoid onClick(View v) {
    //TODO Auto-generated method stub
    Log.v("Mp3playerbt2","Clicked");
    try{
     musicControlService.stopMusic();
     bt1.setImageResource(R.drawable.ibt1);
    }catch (RemoteException e) {
     //TODO Auto-generated catch block
     e.printStackTrace();
    }
   }

  });
}

@Override
protected void onStop() {
  // TODO Auto-generated methodstub
  super.onStop();
  Log.v("Mp3Player","Stop");
}

@Override
protected void onDestroy() {
  // TODO Auto-generated methodstub
  unbindService(sc);
  super.onDestroy();
  Log.v("Mp3Player","Destroy");
}
}