Draw with QPainter

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.