空指针尝试访问活动时异常

Question

我在尝试访问我的活动并更改一些整数时遇到空指针异常。这是它的样子：主要活动.java

    public class MainActivity extends Activity {
    public static SoundManager mSoundManager = new SoundManager();
    private static final String TAG = MainActivity.class.getSimpleName();

     private MainGamePanel gamePanel;
     SharedPreferences myPrefs;
     public int win = 0;
     public int fail = 0;
     int wins = 0;
     int fails = 0;

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // requesting to turn the title OFF
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    // making it full screen
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
    // set our MainGamePanel as the View
    setContentView(new MainGamePanel(this));
    myPrefs = this.getSharedPreferences("hgbdata", 0);
        try {
        wins = myPrefs.getInt("wins", 0);
        fails = myPrefs.getInt("fails", 0);
        if ((wins != 0) && (fails != 0)) {
        gamePanel.winn = wins;
        gamePanel.failn = fails;
        }
        } catch (NullPointerException npe) {
            Log.d(TAG, "Nothing to load");
        }
    //INIT SOUND
    mSoundManager.initSounds(getBaseContext());
    //SOUNDS
    mSoundManager.addSound(1, R.raw.draw);
    mSoundManager.addSound(2, R.raw.cheer);
    mSoundManager.addSound(3, R.raw.boo);
    }
. . .

public void win() {
    win++;
}
public void fail() {
    fail++;
}

}

这是我尝试从以下位置访问活动的地方：主游戏面板.java

public class MainGamePanel extends SurfaceView implements
SurfaceHolder.Callback {
private static final String TAG = MainGamePanel.class.getSimpleName();
private MainThread thread;
private MainActivity activity;
. . .
public void update() {
//somewhere inside the update()
activity.win();
. . .
activity.fail();
}
}

这是日志：

11-18 10:23:47.336: D/MainThread(1190): Starting game loop
11-18 10:23:47.336: D/MainThread.initTimingElements()(1190): Timing elements for stats initialised
11-18 10:23:47.386: D/gralloc_goldfish(1190): Emulator without GPU emulation detected.
11-18 10:24:19.925: D/dalvikvm(1190): GC_CONCURRENT freed 356K, 2% free 28540K/28999K, paused 132ms+30ms, total 441ms
11-18 10:24:20.965: W/dalvikvm(1190): threadid=13: thread exiting with uncaught exception (group=0x40a13300)
11-18 10:24:20.965: E/AndroidRuntime(1190): FATAL EXCEPTION: Thread-105
11-18 10:24:20.965: E/AndroidRuntime(1190): java.lang.NullPointerException
11-18 10:24:20.965: E/AndroidRuntime(1190):     at com.nti.hanga.gubbe.MainGamePanel.update(MainGamePanel.java:591)
11-18 10:24:20.965: E/AndroidRuntime(1190):     at com.nti.hanga.gubbe.MainThread.run(MainThread.java:92)
11-18 10:24:21.235: I/AndroidRuntime(1190): VM exiting with result code 0, cleanup skipped.

MainGamePanel.java:591 activity.win();

谢谢你的帮助。

Answer 1

您甚至不应该尝试从 SurfaceView 引用您的活动。

定义接口并使用回调让活动知道游戏已结束。

public Interface GameOverListener {
    void onGameOver(boolean won);
}

在自定义曲面视图中

ArrayList<GameOverListener > listeners = new ArrayList<GameOverListener >();
...
public void setGameOverListener(GameOverListener listener){
    listeners.add(listener);
}

在更新事件中

for (GameOverListener listener:listeners){
   listener.onGameOver(gameWon?true:false); // here you pass true if they won, false if they lost
}

在您的活动中：

public class MainActivity extends Activity implements GameOverListener {
...
@Override
public void onCreate(Bundle savedInstanceState) 
{
    ... 
    gamePanel.setGameOverListener(this);
    ...
}
public void onGameOver(boolean won){
   if (won){
      // they won!
   } else {
      // they lost!
   }
}

您可以通过添加 removeGameOverListener 并检查是否在 setGameOverListener 中两次添加相同的侦听器来改进图面视图类。

Answer 2

如果activity.win()或activity.fail()在MainGamePanel.java文件的第 591 行，则可能意味着activity == null .您确定已初始化它吗？