Android多媒體學習六：利用Service實現背景音樂的播放

Android同意我們使用Service組件來完畢后台任務。這些任務的同意不會影響到用戶其它的交互。

 

1、Activity類

 package demo.camera;
 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.view.View;
 /**
  * 演示Activity怎樣利用Service來完畢后台Audio的播放功能
  * 同一時候怎樣將Service和Activity進行綁定
  * @author Administrator
  *
  */
 public class BackgroundAudioDemo extends Activity {

     private AudioService audioService;

     //使用ServiceConnection來監聽Service狀態的變化
     private ServiceConnection conn = new ServiceConnection() {

         @Override
         public void onServiceDisconnected(ComponentName name) {
             // TODO Auto-generated method stub
             audioService = null;
         }

         @Override
         public void onServiceConnected(ComponentName name, IBinder binder) {
             //這里我們實例化audioService,通過binder來實現
             audioService = ((AudioService.AudioBinder)binder).getService();

         }
     };

     public void onCreate(Bundle savedInstanceState){
         super.onCreate(savedInstanceState);
         setContentView(R.layout.back_audio);
     }


     public void onClick(View v){
         int id = v.getId();
         Intent intent = new Intent();
         intent.setClass(this, AudioService.class);
         if(id == R.id.btn_start){
             //啟動Service。然后綁定該Service，這樣我們能夠在同一時候銷毀該Activity，看看歌曲是否還在播放
             startService(intent);
             bindService(intent, conn, Context.BIND_AUTO_CREATE);
             finish();
         }else if(id == R.id.btn_end){
             //結束Service
             unbindService(conn);
             stopService(intent);
             finish();
         }else if(id == R.id.btn_fun){
             audioService.haveFun();
         }
     }
 }

2、Service類

 package demo.camera;
 import android.app.Service;
 import android.content.Intent;
 import android.media.MediaPlayer;
 import android.os.Binder;
 import android.os.IBinder;
 import android.widget.MediaController.MediaPlayerControl;
 /**
  * 為了能夠使得在后台播放音樂，我們須要Service
  * Service就是用來在后台完畢一些不須要和用戶交互的動作
  * @author Administrator
  *
  */
 public class AudioService extends Service implements MediaPlayer.OnCompletionListener{

     MediaPlayer player;

     private final IBinder binder = new AudioBinder();
     @Override
     public IBinder onBind(Intent arg0) {
         // TODO Auto-generated method stub
         return binder;
     }
     /**
      * 當Audio播放完的時候觸發該動作
      */
     @Override
     public void onCompletion(MediaPlayer player) {
         // TODO Auto-generated method stub
         stopSelf();//結束了。則結束Service
     }

     //在這里我們須要實例化MediaPlayer對象
     public void onCreate(){
         super.onCreate();
         //我們從raw目錄中獲取一個應用自帶的mp3文件
         player = MediaPlayer.create(this, R.raw.tt);
         player.setOnCompletionListener(this);
     }

     /**
      * 該方法在SDK2.0才開始有的。替代原來的onStart方法
      */
     public int onStartCommand(Intent intent, int flags, int startId){
         if(!player.isPlaying()){
             player.start();
         }
         return START_STICKY;
     }

     public void onDestroy(){
         //super.onDestroy();
         if(player.isPlaying()){
             player.stop();
         }
         player.release();
     }

     //為了和Activity交互，我們須要定義一個Binder對象
     class AudioBinder extends Binder{

         //返回Service對象
         AudioService getService(){
             return AudioService.this;
         }
     }

     //后退播放進度
     public void haveFun(){
         if(player.isPlaying() && player.getCurrentPosition()>2500){
             player.seekTo(player.getCurrentPosition()-2500);
         }
     }
 }

3、在清單文件AndroidManifest.xml中配置Service

 

        <service 
            android:name=".AudioService" />