简单的音乐播放

使用MediaPlayer，代码不全，按钮没有初始化

public class startvideo extends Activity implements OnClickListener,
        OnPreparedListener, OnErrorListener, OnCompletionListener {

    private Button btplay, btpause, btnext, btprev;
    private MediaPlayer mp;
    private int index = 0;
    private ArrayList<String> mplist = new ArrayList<String>();
    private boolean isPsuse=false;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        mp = new MediaPlayer();
        initMusic();

    }

    private void initMusic() {
        String path = Environment.getExternalStoragePublicDirectory(
                Environment.DIRECTORY_MUSIC).getPath();
        mplist.add(path + File.separator + "a.mp3");
        mplist.add(path + File.separator + "b.mp3");
        mplist.add(path + File.separator + "c.mp3");
    }

    @Override
    public void onCompletion(MediaPlayer arg0) {
        // 播放完成
        next();
    }

    @Override
    public boolean onError(MediaPlayer arg0, int arg1, int arg2) {
        // 播放报错
        mp.reset();
        return true;
    }

    @Override
    public void onPrepared(MediaPlayer arg0) {
        // 播放准备
        mp=new MediaPlayer();
    }

    public void paly(){
        if(isPsuse){
            mp.start();
            isPsuse=false;
        }else{
            Start();
            isPsuse=false;
        }
    }
    //暂停功能
    public void pause(){
        if(mp.isPlaying()){
            mp.pause();
            isPsuse=true;
        }
    }
    //下一首
    public void next(){
        if(index-1>0){
            index--;
        }else{
            index=mplist.size()-1;
        }
        Start();
        isPsuse=false;
    }
    //上一首
    public void prev(){
        if(index<mplist.size()-1){
            index++;
        }else{
            index=0;
        }
        Start();
        isPsuse=false;
    }
    //从头开始
    public void Start(){
        if(index<mplist.size()){
            String string = mplist.get(index);
            if(mp.isPlaying()){
            mp.reset(); 
            }
            try {
                mp.setDataSource(string);
                mp.prepareAsync();
                mp.setOnPreparedListener(new OnPreparedListener() {

                    @Override
                    public void onPrepared(MediaPlayer arg0) {
                        // TODO Auto-generated method stub
                    mp.start(); 
                    }
                });
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 
        }
    }

    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        switch (v.getId()) {
        case R.id.play:
            mp.start();
            break;
        case R.id.next:
            next();
            break;
        case R.id.paues:
            pause();
            break;
        case R.id.prev:
            prev();
            break;
        default:
            break;
        }
    }

}