问使用mediaplayer类播放外部SD卡中的歌曲，但无法播放

EN

public class PlaySong {

    MediaPlayer mp;
    Context context;
    String  title;
    public PlaySong(Context context,String title)
    {
        this.title=title;
        this.context=context;
    }

    public void play_Song()
    {
        //Toast.makeText(context, "Yes", 0).show();
        String [] str=title.split("-");
        String name=str[0];

        //Toast.makeText(context, ""+name, 0).show();
        //mp = new MediaPlayer();
        try
        {
        mp = MediaPlayer.create(context, Uri.parse(Environment.getExternalStorageDirectory().getPath()+ "/songs/"+name+".mp3"));
        //mp.setAudioStreamType(AudioManager.STREAM_MUSIC);
        //mp.setLooping(true);
        mp.start();
        }
        catch(Exception ex) 
        {
            Toast.makeText(context, ""+ex, 0).show();

        }
    }

}