Android多媒体学习六：利用Service实现背景音乐的播放

Android同意我们使用Service组件来完毕后台任务。这些任务的同意不会影响到用户其它的交互。

 

1、Activity类

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怎样利用Service来完毕后台Audio的播放功能
 * 同一时候怎样将Service和Activity进行绑定
 * @author Administrator
 *
 */
public class BackgroundAudioDemo extends Activity {

    private AudioService audioService;

    //使用ServiceConnection来监听Service状态的变化
    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) {
            //这里我们实例化audioService,通过binder来实现
            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){
            //启动Service。然后绑定该Service，这样我们能够在同一时候销毁该Activity，看看歌曲是否还在播放
            startService(intent);
            bindService(intent, conn, Context.BIND_AUTO_CREATE);
            finish();
        }else if(id == R.id.btn_end){
            //结束Service
            unbindService(conn);
            stopService(intent);
            finish();
        }else if(id == R.id.btn_fun){
            audioService.haveFun();
        }
    }
}

2、Service类

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;
/**
 * 为了能够使得在后台播放音乐，我们须要Service
 * Service就是用来在后台完毕一些不须要和用户交互的动作
 * @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;
    }
    /**
     * 当Audio播放完的时候触发该动作
     */
    @Override
    public void onCompletion(MediaPlayer player) {
        // TODO Auto-generated method stub
        stopSelf();//结束了。则结束Service
    }

    //在这里我们须要实例化MediaPlayer对象
    public void onCreate(){
        super.onCreate();
        //我们从raw目录中获取一个应用自带的mp3文件
        player = MediaPlayer.create(this, R.raw.tt);
        player.setOnCompletionListener(this);
    }

    /**
     * 该方法在SDK2.0才開始有的。替代原来的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();
    }

    //为了和Activity交互，我们须要定义一个Binder对象
    class AudioBinder extends Binder{

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

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

3、在清单文件AndroidManifest.xml中配置Service

 

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