用QPainter绘制

Question

I need draw with QPainter , but when I try to do it not in

void paintEvent( QPaintEvent* )

I catch error:

QPainter::setPen: Painter not active

QPainter::setBrush: Painter not active

Can I use QPainter not in void paintEvent( QPaintEvent* ) ?

Thank you.

Answer 1

You are using a widget as the paint device for QPainter . In this case, QPainter can usually only be used within the context of the widget's paint event. The QPainter documentation has the following to say about this:

Warning: When the paintdevice is a widget, QPainter can only be used inside a paintEvent() function or in a function called by paintEvent(); that is unless the Qt::WA_PaintOutsidePaintEvent widget attribute is set. On Mac OS X and Windows, you can only paint in a paintEvent() function regardless of this attribute's setting.

It is possible to use QPainter outside a paint event by setting another paint device for QPainter , for example a QPixmap .