NullPointerException,它不指向我的代码中的任何行

Question

我正在制作一个游戏,玩家可以在屏幕上拖放东西.我有一个私有方法,允许我为玩家可以移动的任何项目模拟拖放事件.对于拖动,我实际上离开视图他们触摸它的位置并创建一个新的ImageView,并从触摸的视图中将drawable设置为drawingCache,然后在他们的手指上围绕屏幕移动这个新创建的ImageView.当你松开手指(放下视图)时,我打电话myLayout.remove(movingImg);让它离开屏幕.我有一个问题,如果我开始一个模拟的拖动事件,然后手动拿起其他一个项目,我在myLayout.remove()调用上得到一个空指针,这里是来自日志的跟踪:

04-06 10:37:43.610: ERROR/AndroidRuntime(23203): java.lang.NullPointerException
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2122)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.drawChild(ViewGroup.java:2506)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2123)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.drawChild(ViewGroup.java:2506)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2123)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.drawChild(ViewGroup.java:2506)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2123)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.drawChild(ViewGroup.java:2506)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2123)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.View.draw(View.java:9032)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.widget.FrameLayout.draw(FrameLayout.java:419)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at com.android.internal.policy.impl.PhoneWindow$DecorView.draw(PhoneWindow.java:1910)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewRoot.draw(ViewRoot.java:1608)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewRoot.performTraversals(ViewRoot.java:1329)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1944)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.os.Looper.loop(Looper.java:126)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at android.app.ActivityThread.main(ActivityThread.java:3997)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at java.lang.reflect.Method.invokeNative(Native Method)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at java.lang.reflect.Method.invoke(Method.java:491)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
04-06 10:37:43.610: ERROR/AndroidRuntime(23203):     at dalvik.system.NativeStart.main(Native Method)

跟踪不指向我的活动中的任何位置.只要它试图在模拟拖动视图上调用myLayout.remove(),就会抛出异常.我用try/catch包围了这一行,但没有做任何事情.我知道这是给我带来麻烦的线路,因为如果我发表评论然后我没有得到例外,但显然我的观点永远不会从屏幕上移除.我正在摩托罗拉xoom上构建这个应用程序,但我不确定这是否是特定于设备的问题.有谁知道这里会发生什么？

这是调用.removeView()的地方:

        @Override
        public void onAnimationEnd(Animation animation) {
            // TODO Auto-generated method stub
            Log.i(myTag, "Animation End");

            try {
                //myLayout.removeView(simulateMovingImg); //This is the line that is throwing a null pointer
                simulateMovingImg.setVisibility(View.GONE); //This is how I am currently getting around the issue
                params = new LayoutParams(oneImg.getWidth(),oneImg.getHeight()); // While its moving it appears larger than normal
                 simulateMovingImg.setLayoutParams(params);                     //  so I set it back to the normal size
                 if(whichTarget == true){
                     targetImg.setImageDrawable(simulateMovingImg.getDrawable()); //targetImg is one of the 'drop zones' so I set its 
                                                                                //  drawable to make it seem like the view was 'dropped' into this zone
                 }else{
                     target1Img.setImageDrawable(simulateMovingImg.getDrawable()); // same with target1Img. 
                 }
            } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

             iAmDone = true;
        }
    });

这是一个用于翻译动画的AnimationListener,它将我的ImageView从它开始的位置移动到它被"放弃"的位置

Answer 1

当您在animationEnd中更改视图层次结构时,Android将发生异常.

你所要做的就是推迟你的电话:

@Override
public void onAnimationEnd(Animation animation) {
    new Handler().post(new Runnable() {
        public void run() {
            myLayout.removeView(simulateMovingImg);
        }
    });
}