java - 应用程序子类中的奇怪异常

Question

Crashlytics 向我发送了一个我不理解且无法模拟的堆栈跟踪:

Fatal Exception: java.lang.NullPointerException
at lelisoft.com.lelimath.helpers.LeliMathApp.playSound(LeliMathApp.java:81)
at lelisoft.com.lelimath.fragment.PuzzleFragment$HandleClick.onClick(PuzzleFragment.java:158)
at android.view.View.performClick(View.java:4276)

LeliMath 是 android 应用程序子类，只需初始化一次。我理解这是一种单例。失败的代码在创建时被初始化并且永远不会为空。

public class LeliMathApp extends Application  {
  private Map<Integer, Integer> mSounds = new HashMap<>();
  private boolean soundEnabled;

public void onCreate() {
    SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
    soundEnabled = sharedPref.getBoolean(GamePreferenceActivity.KEY_SOUND_ENABLED, true);
    setSoundLevel(sharedPref.getInt(GamePreferenceActivity.KEY_SOUND_LEVEL, 50));
    toggleSound(soundEnabled);
}

public void playSound(int resourceId) {
    if (soundEnabled) {
        int soundId = mSounds.get(resourceId); // NPE here
        mShortPlayer.play(soundId, soundLevel, soundLevel, 0, 0, 1);
    }
}

public void toggleSound(boolean state) {
    log.debug("Toggle sound support");
    if (! state && mShortPlayer != null) {
        mShortPlayer.release();
        mShortPlayer = null;
        mSounds.clear();
    } else if (state && mShortPlayer == null) {
        if (Build.VERSION.SDK_INT >= 23) {
            mShortPlayer = new SoundPool.Builder().build();
        } else {
            //noinspection deprecation
            mShortPlayer = new SoundPool(1, AudioManager.STREAM_MUSIC, 0);
        }
        mSounds.put(R.raw.correct, this.mShortPlayer.load(this, R.raw.correct, 1));
        mSounds.put(R.raw.incorrect, this.mShortPlayer.load(this, R.raw.incorrect, 1));
        mSounds.put(R.raw.victory, this.mShortPlayer.load(this, R.raw.victory, 1));
    }
}

它不会在 NPE 上失败，但它确实失败了。任何想法？我很想查看日志，但我不知道出现此错误的用户。

更新:这是对此方法的调用列表

LeliMathApp.getInstance().playSound(R.raw.correct);
LeliMathApp.getInstance().playSound(R.raw.incorrect);
LeliMathApp.getInstance().playSound(R.raw.victory);

Answer 1

mSounds.get(resourceId);当 HashMap 中不存在该键时返回 null。因此出现空指针异常。

要解决这个问题，你需要做这样的事情。

int soundId = -1;

Integer tempSoundId = mSounds.get(resourceId);
if(tempSoundId != null)
  soundId = tempSoundId;

This is an expected java behaviour since we are trying to unbox a null value.