[FIXED] Qt DragLeaveEvent not being called when leaving with a drag operation

Issue

I have a row of buttons, each of which can accept drops. However, when I leave a button with my cursor with another button being dragged, the 'dragLeaveEvent' is not being called.

class Button(QtGui.QPushButton):
    def __init__(self):
        super(Button, self).__init__()
        self.setAcceptDrops(True)

    def mousePressEvent(self, event):
        if event.button() == QtCore.Qt.LeftButton:
            drag = QtGui.QDrag(self)
            mime = QtCore.QMimeData()
            mime.setText("f")
            drag.setMimeData(mime)
            drag.exec_()

    def dragEnterEvent(self, event):
        print "enter"

    def dragLeaveEvent(self, event):
        print "leave"


class MainWindow(QtGui.QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.mainLayout = QtGui.QVBoxLayout()
        self.setLayout(self.mainLayout)
        for i in range(10):
            btn = Button()
            self.mainLayout.addWidget(btn)


if __name__ == '__main__':
    import sys
    app = QtGui.QApplication(sys.argv)
    win = MainWindow()
    win.show()
    sys.exit(app.exec_())

Solution

As the documentation about dragEnterEvent() reports (it's from Qt5, but the same was valid for Qt4 also):

If the event is ignored, the widget won't receive any drag move events.

Note: any drag move events.
This also means drop events.

By default, all drag events are ignored for most widgets if the drag enter event is not accepted, so if you want to receive all events (including the leave event) that first event must be accepted.

class Button(QtGui.QPushButton):
    # ...
    def dragEnterEvent(self, event):
        event.accept()
        print "enter"

Answered By - musicamante