java - 运行游戏应用程序时出现空指针异常错误

Question

目前我正在为一些网站开发应用程序，但我对开发游戏应用程序有点疯狂，因此按照教程在第一级的 Canvas 上创建了一个图像，并在下一个级别中创建了图像必须为此移动，也给出了编码，但是当我运行应用程序时，它会强制关闭。 这是我的代码。

public class GameView extends SurfaceView {

private Bitmap bmp;
private SurfaceHolder holder;
private GameLoopThread gameLoopThread;
private int x = 0;  

public GameView(Context context) {
    super(context);
 gameLoopThread = new GameLoopThread()
    holder = getHolder();
    holder.addCallback(new SurfaceHolder.Callback() {

           @Override
           public void surfaceDestroyed(SurfaceHolder holder) {
               boolean retry = true;
               gameLoopThread.setRunning(false); 
               while (retry) {
                      try {
                            gameLoopThread.join();
                            retry = false;
                      } catch (InterruptedException e) {
                      }
               }
           }

        @Override
           public void surfaceCreated(SurfaceHolder holder) {
               gameLoopThread.setRunning(true);
               gameLoopThread.start();
           }


           @Override
           public void surfaceChanged(SurfaceHolder holder, int format,
                         int width, int height) {
           }

    });

    bmp = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
}
@Override
protected void onDraw(Canvas canvas) {
    canvas.drawColor(Color.BLACK);
    if (x < getWidth() -  bmp.getWidth()) {
        x++;
 }
    canvas.drawBitmap( bmp, x, 10, null);
}

线程类

public class GameLoopThread extends Thread{
private GameView view;
private boolean running = false;

public GameLoopThread(GameView view) {
      this.view = view;
}


public void setRunning(boolean run) {
      running = run;
}



@SuppressLint("WrongCall")
@Override

public void run() {
      while (running) {
             Canvas c = null;
             try {
                    c = view.getHolder().lockCanvas();
                    synchronized (view.getHolder()) {
                           view.onDraw(c);
                    }

             } finally {
                    if (c != null) {
                           view.getHolder().unlockCanvasAndPost(c);
                    }
             }
      }
}

logcat结果

03-21 23:38:26.341: E/AndroidRuntime(754): FATAL EXCEPTION: main
03-21 23:38:26.341: E/AndroidRuntime(754): java.lang.NullPointerException
03-21 23:38:26.341: E/AndroidRuntime(754):  at com.killthemall.GameView$1.surfaceCreated(GameView.java:40)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.SurfaceView.updateWindow(SurfaceView.java:543)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.SurfaceView.dispatchDraw(SurfaceView.java:348)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.ViewGroup.drawChild(ViewGroup.java:1644)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.View.draw(View.java:6883)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.widget.FrameLayout.draw(FrameLayout.java:357)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.ViewGroup.drawChild(ViewGroup.java:1646)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.ViewGroup.dispatchDraw(ViewGroup.java:1373)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.View.draw(View.java:6883)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.widget.FrameLayout.draw(FrameLayout.java:357)
03-21 23:38:26.341: E/AndroidRuntime(754):  at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1862)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.ViewRoot.draw(ViewRoot.java:1522)
03-21 23:38:26.341: E/AndroidRuntime(754):  at  android.view.ViewRoot.performTraversals(ViewRoot.java:1258)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.view.ViewRoot.handleMessage(ViewRoot.java:1859)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-21 23:38:26.341: E/AndroidRuntime(754):  at android.os.Looper.loop(Looper.java:123)
 03-21 23:38:26.341: E/AndroidRuntime(754):     at android.app.ActivityThread.main(ActivityThread.java:3683)
03-21 23:38:26.341: E/AndroidRuntime(754):  at java.lang.reflect.Method.invokeNative(Native Method)
03-21 23:38:26.341: E/AndroidRuntime(754):  at java.lang.reflect.Method.invoke(Method.java:507)
 03-21 23:38:26.341: E/AndroidRuntime(754):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
 03-21 23:38:26.341: E/AndroidRuntime(754):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-21 23:38:26.341: E/AndroidRuntime(754):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

com.killthemall.GameView$1.surfaceCreated(GameView.java:40)

这告诉你第40行的surfaceCreated方法中发生了空指针。查看该方法，第一行执行了gameLoopThread.setRunning，因此可以如果 gameLoopThread 为 null，则失败并出现空指针异常。

查看代码，您没有初始化 gameLoopThread，因此它的默认值为 null。在 GameView 的构造函数中添加行 gameLoopThread = new GameLoopThread()。