媒体播放器给我空指针异常

Question

I want my code to play a sound file at MAX volume when a button is pressed. My code works perfectly fine just playing the sound file, but when I throw in originalVolume

int originalVolume = mAudioManager
                        .getStreamVolume(AudioManager.STREAM_MUSIC);
                mAudioManager.setStreamVolume(AudioManager.STREAM_MUSIC,
                        mAudioManager
                                .getStreamMaxVolume(AudioManager.STREAM_MUSIC),
                        0);

My program crashes upon the click of the button.

public class VolumeUp extends Activity {
    TextView text;
    int counter = 0;
    private AudioManager mAudioManager;
    MediaPlayer mediaPlayer = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        text = (TextView) findViewById(R.id.hello);

        text.setOnClickListener(new OnClickListener() {
            public void onClick(View view) {
                int originalVolume = mAudioManager
                        .getStreamVolume(AudioManager.STREAM_MUSIC);
                mAudioManager.setStreamVolume(AudioManager.STREAM_MUSIC,
                        mAudioManager
                                .getStreamMaxVolume(AudioManager.STREAM_MUSIC),
                        0);

                mediaPlayer = MediaPlayer.create(VolumeUp.this,
                        R.raw.policesiren);
                mediaPlayer.setScreenOnWhilePlaying(true);
                mediaPlayer.setLooping(true);// we set the sound to loop.
                mAudioManager.setStreamVolume(AudioManager.STREAM_MUSIC,
                        originalVolume, 0);
                mediaPlayer.start();

            }
        });

    }

Answer 1

From code you have shown above, mAudioManager is null all the time. So its obvious why you get NPE.

you forgot this line:

mAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);