QGraphicsGridLayout works in PySide but not PyQt4

Question

I've been trying for hours to get QGraphicsGridLayout to work with PyQt4. I have PySide installed so I switched the imports to that for a quick check and it worked as expected! For the code below, when PySide is used, the paint method on the RectangleWidget is called as expected but when you use PyQt4 the paint method is never called.

I know that the RectangleWidget should override some more virtual methods for a proper implementation but I was stripping things out to try and get the minimal amount of code to narrow down the problem.

from PySide import QtGui, QtCore
# from PyQt4 import QtGui, QtCore


class RectangleWidget(QtGui.QGraphicsWidget):
    def __init__(self, rect, parent=None):
        super(RectangleWidget, self).__init__(parent)
        self.rect = rect

    def paint(self, painter, *args, **kwargs):
        print('Paint Called')
        painter.drawRect(self.rect)


class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.central_widget = QtGui.QWidget(self)
        central_layout = QtGui.QHBoxLayout()
        self.central_widget.setLayout(central_layout)
        self.setCentralWidget(self.central_widget)
        self.resize(500, 500)

        self.view = QtGui.QGraphicsView()
        self.scene = QtGui.QGraphicsScene()
        self.view.setScene(self.scene)

        panel = QtGui.QGraphicsWidget()
        self.scene.addItem(panel)

        layout = QtGui.QGraphicsGridLayout()
        panel.setLayout(layout)

        for i in range(4):
            for j in range(4):
                rectangle = RectangleWidget(QtCore.QRectF(0, 0, 50, 50))
                layout.addItem(rectangle, i, j)

        central_layout.addWidget(self.view)

if __name__ == '__main__':
    import sys

    app = QtGui.QApplication(sys.argv)
    widget = MainWindow()
    widget.show()
    app.exec_()

Any help is appreciated! I would like to maintain compatibility with both PyQt4 and PySide so continuing using PySide only is not really an ideal solution. Thanks

Answer 1

The QGraphicsGridLayout takes ownership of the items added to it (see the docs for further details).

In your example, it would seem that all the RectangleWidget items are in danger of being garbage-collected once they go out of scope. So if you give them a parent:

    rectangle = RectangleWidget(QtCore.QRectF(0, 0, 50, 50), panel)

all should be well.