NullPointerException 不指向我的代码中的任何行 [英] NullPointerException that doesn't point to any line in my code
问题描述
我正在开发一款玩家可以在屏幕上拖放东西的游戏.我有一个私有方法，它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，我实际上是将他们触摸的视图留在原处，并使用触摸视图创建一个新的 ImageView 并将可绘制对象设置为drawingCache，然后跟随他们的手指在屏幕上移动这个新创建的 ImageView.当您松开手指(放下视图)时，我正在调用 myLayout.remove(movingImg); 将其从屏幕上移开.我遇到了一个问题，如果我开始模拟拖动事件，然后手动拿起其他项目之一，我在 myLayout.remove() 调用中得到一个空指针，这是来自 Log 的跟踪:
I am working on a game where the player can drag and drop things around the screen. I've got a private method which allows me to simulate a drag/drop event for any of the items that the player can move around. For the dragging I am actually leaving the view that they touched where it is and creating a new ImageView with and setting the drawable to the drawingCache from the touched view, then moving this newly created ImageView around the screen following their finger. When you release your finger (drop the view) I am calling myLayout.remove(movingImg); to get it off of the screen. I am having an issue where if I start a simulated drag event and then manually pick up one of the other items I am getting a null pointer on the myLayout.remove() call, here is the trace from Log:
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)
跟踪没有指向我的活动中的任何地方.每当它尝试在模拟拖动视图上调用 myLayout.remove() 时，就会抛出异常.我用 try/catch 包围了这条线，但什么也没做.我知道这是给我带来麻烦的行，因为如果我将其注释掉，那么我不会得到异常，但显然我的视图永远不会从屏幕上删除.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设备特定的问题.有人知道这里会发生什么吗?
The trace doesn't point to anywhere inside my activity. The exception gets thrown whenever the it tries to call myLayout.remove() on the simulated dragging view. I surrounded this line with a try / catch but that did nothing. I know that this is the line thats giving me trouble because if I comment it out then I don't get an exception but obviously then my view never gets removed from the screen. I am building this app on a Motorola xoom, I am not sure if this is a device specific issue or not though. Does anyone know what might be going on here?
这是调用 .removeView() 的地方:
This is the where the .removeView() is getting called from:
@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;
}
});
这是在 AnimationListener 中，用于翻译动画，该动画将我的 ImageView 从它开始的位置移动到它被放下"的位置
That is inside an AnimationListener for the translate animation that is moving my ImageView from where it starts to where it is getting 'dropped'
推荐答案
Android 在 animationEnd 中更改视图层次结构时会出现异常.
Android will make an exception when you change the view hierarchy in animationEnd.
你所要做的就是像这样推迟你的电话:
All you have to do is to postpone your call like this :
@Override
public void onAnimationEnd(Animation animation) {
new Handler().post(new Runnable() {
public void run() {
myLayout.removeView(simulateMovingImg);
}
});
}
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