將setDataSource與URI一起使用時，Android NullPointerException

Question

大家好，我正在為Android制作音樂播放器，當我去選擇要播放的歌曲時，應用崩潰並產生錯誤：

09-16 13:10:08.671: I/System.out(22932): Reset worked
09-16 13:10:08.671: I/System.out(22932): com.example.taptwisttunes.Song@42d97240
09-16 13:10:08.671: I/System.out(22932): about to load song
09-16 13:10:08.671: I/System.out(22932): content://media/external/audio/media/23657
09-16 13:10:08.671: I/System.out(22932): content://media/external/audio/media/23657
09-16 13:10:08.671: D/AndroidRuntime(22932): Shutting down VM
09-16 13:10:08.671: W/dalvikvm(22932): threadid=1: thread exiting with uncaught exception (group=0x41fee700)
09-16 13:10:08.676: E/AndroidRuntime(22932): FATAL EXCEPTION: main
09-16 13:10:08.676: E/AndroidRuntime(22932): java.lang.IllegalStateException: Could not execute method of the activity

這是我的playSong方法，有人知道我在做什么錯嗎？

public void playSong(){ //this method plays the song by retrieving ID and modeling it as uri
        //player.reset(); //resets media player
        System.out.println("Reset worked");
        Song playSong = songs.get(sPos); // retrieves song to be played
        System.out.println(playSong);
        long currSong = playSong.getId();
        System.out.println("about to load song");
        Uri trackUri = ContentUris.withAppendedId(android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, currSong);  
        System.out.println(trackUri);
        System.out.println(trackUri.toString());
        //try block not sure if uri will work as a data source

        try{
            player.setDataSource(this.getApplicationContext(), trackUri);
        }
        catch(Exception e){
            Log.e("Music Service", "There has been an error setting the data source", e);
        } 
        player.prepareAsync();
    }

Answer 1

MediaPlayer#prepareAsync引發IllegalStateException ，您需要處理該異常或向您的方法聲明中添加引發，因此方法的調用者將處理該異常。 是你做的嗎？ 就像是 ：

try{
player.prepareAsync();
}
catch(IllegalStateException ise){
//do what you want when this exception is thrown
}

Answer 2

有了錯誤和給出的代碼，我相信您已經調用player實例來播放一些歌曲，而您正在嘗試第二次播放歌曲。

另外，您已經注釋了player.reset().

確保您的player實例為reset（） ， prepare（）並設置為正確播放文件。

下圖來自android開發人員 ，應該可以幫助您更好地理解該概念。