This code for creating a QPolygon in Pyqt is stopping my application! Help?

Question

HI all,

The following code:

self.painter = QtGui.QPainter(self)
self.painter.setRenderHint(QPainter.Antialiasing)
self.painter.translate(482,395)
self.painter.scale(300,300)
self.painter.save()
needle = Qt.QPolygon([QPoint(30, 0), QPoint(-30, 0), QPoint(0, 200)])
self.painter.setBrush(Qt.cyan)
self.painter.setPen(Qt.black)
self.painter.drawPolygon(needle)
self.painter.restore()

is causing my Pyqt application to crash. Does anyone have any idea why? It is part of my ui_form.py file which was automatically spat out by pyuic4. Removing / commenting it out fixes the problem. Yes, I wrote this myself instead of the compiler doing it.

Many thanks!

Answer 1

Save the list which you pass the the constructor of QPolygon in a local variable. I guess that the elements get garbage collected as soon as the call returns so when you draw the polygon, they are no longer around.

points = [QPoint(30, 0), QPoint(-30, 0), QPoint(0, 200)]
needle = Qt.QPolygon(points)