请求音频焦点时出现空指针异常

Question

这是我的代码：

int result = am.requestAudioFocus(audio_listener,AudioManager.STREAM_MUSIC,AudioManager.AUDIOFOCUS_GAIN_TRANSIENT);
if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
    mediaPlayer = MediaPlayer.create(NumbersActivity.this,onwhich_isClickedN.getAudiofile());
    mediaPlayer.start();
    mediaPlayer.setOnCompletionListener(on_comp);
    }

这是错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'int android.media.AudioManager.requestAudioFocus(android.media.AudioManager$OnAudioFocusChangeListener, int, int)' on a null object reference

Answer 1

在使用之前，请检查您是否已初始化AudioManager am = (AudioManager) getActivity().getSystemService(Context.AUDIO_SERVICE);

以下是tutorialspoint website可能对您有所帮助的更多信息。