set transparent background for custom widget is not effective

hello, I made a custom widget named PopUpIrregularWidget, I want to make this customed widget has transparent background, and I use the code

Code:

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this->setStyleSheet("PopUpIrregularWidget{background : transparent;}");

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, but the background is white, not transparent.
So how to make the custom widget background transparent?
or I lost something ?

What is PopUpIrregularWidget? Base class? Have you reimp the paint event? Try to use QPalette.

The PopUpIrregularWidget just extends QWidget, a custom QWidget.And I use the code

Code:

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style()->drawPrimitive(QStyle::PE_Widget, &opt, &painter, this);

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in the paintEvent.