英文:
Why the view provided by onViewCreated() works as non null for one method and as null for the other method?
问题
为什么在onViewCreated() 方法中提供的视图在简单的findViews(View view) 方法中可以正常工作，但对于另一个用于OnWindowFocusChangeListener(...) 的方法会抛出NullPointerException？
我不知道该如何解决这个问题。我的意思是，我不知道要尝试什么。
@Override
public void onViewCreated(@NonNull final View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
findViews(view);
.....................................
view.getViewTreeObserver().addOnWindowFocusChangeListener(new ViewTreeObserver.OnWindowFocusChangeListener() {
@Override
public void onWindowFocusChanged(final boolean hasFocus) {
actionsForUISizesOptimizationProcess(hasFocus, view);
}
});
}
void actionsForUISizesOptimizationProcess(boolean hasFocus, View view){
FrameLayout fragmentContainer = view.findViewById(R.id.fragmentContainer); // 调试显示此行中的视图为空
int displayWidth = fragmentContainer.getWidth(); // java.lang.NullPointerException: 尝试在空对象引用上调用虚拟方法'int android.widget.FrameLayout.getWidth()'
int displayHeight = fragmentContainer.getHeight();
...........................................
}
英文:
Why the view provided by onViewCreated() works as non null in simple findViews(View view) but for the other method which is for OnWindowFocusChangeListener(...) throws NullPointerException?
I have no idea what to do to solve this problem. I mean, I have no idea what to try.
'''
@Override
public void onViewCreated(@NonNull final View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
findViews(view);
.....................................
view.getViewTreeObserver().addOnWindowFocusChangeListener(new ViewTreeObserver.OnWindowFocusChangeListener() {
@Override
public void onWindowFocusChanged(final boolean hasFocus) {
actionsForUISizesOptimizationProcess(hasFocus,view);
}
});
}
void actionsForUISizesOptimizationProcess(boolean hasFocus, View view){
FrameLayout fragmentContainer = view.findViewById(R.id.fragmentContainer); //debugging showed that the view in this line is null
int displayWidth = fragmentContainer.getWidth(); //java.lang.NullPointerException: Attempt to invoke virtual method 'int android.widget.FrameLayout.getWidth()' on a null object reference
int displayHeight = fragmentContainer.getHeight();
...........................................
}
'''
答案1
得分: 1
view 不是 null。问题出在 actionsForUISizesOptimizationProcess() 这段代码：
fragmentContainer = view.findViewById(R.id.fragmentContainer);
fragmentContainer 为 null。findViewById() 调用返回了 null。
所以，也许在 View 层次结构中没有带有 ID fragmentContainer 的 View？
英文:
view is not null. The problem is this code in actionsForUISizesOptimizationProcess():
fragmentContainer = view.findViewById(R.id.fragmentContainer);
fragmentContainer is null. The call to findViewById() is returning null
So, maybe there is no View with ID fragmentContainer in the View hierarchy?
答案2
得分: 1
在你的XML文件中，检查FrameLayout的ID是否为fragmentContainer，并且是否存在no typo。
英文:
In your xml file, check if the id of your FrameLayout is fragmentContainer and there exists no typo
答案3
得分: 0
在你的XML文件中很可能有一个拼写错误，应该是“fragmentContainer”，这就是为令findViewById()找不到它的原因。
英文:
There is likely a a typo in your XML file where the id is supposed to be fragmentContainer which is why the findViewById() is not finding it.
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