Segmentation fault on Mac OS during drag & drop

remram

Hi,

I found that replacing a widget while a drag is happening can cause a segmentation fault on Mac OS (doesn't happen on my Windows machine). I am replacing it from the parent's widget dragEnterEvent.

I am using PyQt4 4.9.6 with Qt 4.8.3.

Below is an example program that shows the issue; dragging something from the list to the MyWidget on the right will cause a segmentation fault on Mac OS... Even though the child widget shouldn't be concerned by the drag and drop (only the parent accepts and handles it).

I can probably translate it to C++ if needed...

@import sys

from PyQt4 import QtCore, QtGui

class Widget1(QtGui.QWidget):
def init(self):
QtGui.QWidget.init(self)
# If this line is left commented out (which I need it to be), this
# program will crash on Mac OS
#self.setAttribute(QtCore.Qt.WA_TransparentForMouseEvents)
self.setSizePolicy(QtGui.QSizePolicy.MinimumExpanding,
QtGui.QSizePolicy.MinimumExpanding)

def sizeHint(self):
    return QtCore.QSize(100, 100)

def paintEvent(self, event):
    qp = QtGui.QPainter(self)
    qp.setPen(QtGui.QColor(0, 0, 191))
    qp.drawText(0, 0, self.width(), self.height(),
                QtCore.Qt.AlignCenter | QtCore.Qt.TextWordWrap,
                "First widget, drag something here")

class Widget2(QtGui.QWidget):
def init(self):
QtGui.QWidget.init(self)
self.setAttribute(QtCore.Qt.WA_TransparentForMouseEvents)
self.setSizePolicy(QtGui.QSizePolicy.MinimumExpanding,
QtGui.QSizePolicy.MinimumExpanding)

def sizeHint(self):
    return QtCore.QSize(100, 100)

def paintEvent(self, event):
    qp = QtGui.QPainter(self)
    qp.setPen(QtGui.QColor(191, 0, 0))
    qp.drawText(0, 0, self.width(), self.height(),
                QtCore.Qt.AlignCenter | QtCore.Qt.TextWordWrap,
                "Second widget, overlay")

class MyWidget(QtGui.QWidget):
def init(self):
QtGui.QWidget.init(self)
self.setAcceptDrops(True)

    self._scrollarea = QtGui.QScrollArea()
    layout = QtGui.QVBoxLayout()
    layout.addWidget(self._scrollarea)
    self.setLayout(layout)

    self._inner_widget = Widget1()
    self._scrollarea.setWidget(self._inner_widget)

def _set_widget(self, widget):
    self._inner_widget.setParent(None)
    self._inner_widget.deleteLater()
    self._inner_widget = widget
    self._scrollarea.setWidget(widget)
    widget.show()

def dragEnterEvent(self, event):
    self._set_widget(Widget2())
    event.accept()

def dragLeaveEvent(self, event):
    self._set_widget(Widget1())

def dropEvent(self, event):
    self._set_widget(Widget1())
    event.accept()

app = QtGui.QApplication(sys.argv)

listWidget = QtGui.QListWidget()
listWidget.setDragEnabled(True)
listWidget.setDragDropMode(QtGui.QAbstractItemView.DragOnly)
listWidget.addItem("An item")
listWidget.addItem("Other item")

window = QtGui.QWidget()
layout = QtGui.QHBoxLayout()
layout.addWidget(listWidget)
layout.addWidget(MyWidget())
window.setLayout(layout)

window.show()
app.exec_()@

Is this a bug in Qt? How can I get this to work? (I am thinking about making both widgets TransparentForMouseEvents and forwarding manually the mouse events from MyWidget to Widget1... can I make this work?)

Thank you for your time