[Qt-interest] I have a problem for add a custom widget to vboxlayout

[wanneng]

I have a widget A which inherited from the QWidget, and reimplement its 
paintEvent method, others is not changed.
then, I add my custom widget A to a QVboxLayout.

But when I run the program, it show the widget A, but not manage the 
size. Its means that When A is out of the view port, the QVboxLayout 
does not create the scroll bar, I think may be there are some other 
methods needed to reimplemented.

Is there anyone can help me? thank you anyway.

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