PyQt4 drag and drop receives mouseReleaseEvent before dragEnter

Question

I am trying to do drag and drop of rows inside a QTableWidget.

The drag and drop operation itself is working great, but when I click and release the mouse button rapidly on a row , the drop event is never called. Even with the mouse released, the cursor is still in drag mode until I click again.

When I click an release slowly on a row, to select it, the events are: - mousePressEvent - dragEnterEvent - dropEvent

When I click and release rapidly, the events are: - mousePressEvent - mouseReleaseEvent - dragEnterEvent and dropEvent is only called if I click again.

This is probably because the dragEnterEvent (that should never be called, I think) 'hides' the mouseReleaseEvent to the drag operation.

Is there a way to force the end of the drag operation ? or better, to prevent the drag operation to call dragEnterEvent ?

Here is my code:

class DragDropTableWidget(QTableWidget):

    moveRow = pyqtSignal(int, int)

    def __init__(self, parent):
        super(QTableWidget, self).__init__(parent)

        self.setDragEnabled(True)
        self.setAcceptDrops(True)
        self.viewport().setAcceptDrops(True)
        self.setDragDropOverwriteMode(False)
        self.setDropIndicatorShown(True)
        self.setSelectionMode(QAbstractItemView.SingleSelection)
        self.setSelectionBehavior(QAbstractItemView.SelectRows)
        self.setDragDropMode(QAbstractItemView.InternalMove)

        self.released = False

    def mousePressEvent(self, event):
        print('Mouse Press')
        self.released = False

        index = self.indexAt(event.pos())
        if not index.isValid():
            return

        row = index.row()
        self.selectRow(row)

        mime_data = QMimeData()
        mime_data.setData("index", str(row))

        drag = QDrag(self)
        drag.setMimeData(mime_data)
        drag.start(Qt.MoveAction)

    def dragEnterEvent(self, e):
        print('Drag Enter')
        if self.released:
            # todo: cancel drag and drop
            pass
        else:
            e.accept()

    def dragMoveEvent(self, e):
        e.accept()

    def mouseReleaseEvent(self, e):
        print('Mouse release')
        self.released = True

    def dropEvent(self, event):
        print('Drop event')
        if event.source() == self:
            index = self.indexAt(event.pos())
            if not index.isValid():
                event.accept()
                return
            start_index = int(event.mimeData().data("index"))
            if start_index != index.row():
                print ("dropEvent called from row {} on row {}".format(start_index, index.row()))
                self.moveRow.emit(start_index, index.row())

            event.accept()

Thanks a lot

Answer 1

Thank you musicamante for showing me the right direction. This is a working implementation for a QTableWidget with drag and drop support of table rows:

class DragDropTableWidget(QTableWidget):
# signal sent on drag and drop end operation
moveRow = pyqtSignal(int, int)

def __init__(self, parent):
    super(QTableWidget, self).__init__(parent)

    self.setDragEnabled(True)
    self.setAcceptDrops(True)
    self.viewport().setAcceptDrops(True)
    self.setDragDropOverwriteMode(False)
    self.setDropIndicatorShown(True)
    self.setSelectionMode(QAbstractItemView.SingleSelection)
    self.setSelectionBehavior(QAbstractItemView.SelectRows)
    self.setDragDropMode(QAbstractItemView.InternalMove)

def mouseMoveEvent(self, event):
    if event.type() == QEvent.MouseMove and event.buttons() & Qt.LeftButton:
        index = self.indexAt(event.pos())
        if not index.isValid():
            return

        mime_data = QMimeData()
        mime_data.setData("index", str(index.row()))

        drag = QDrag(self)
        drag.setMimeData(mime_data)

        drag.start(Qt.MoveAction)

def dragEnterEvent(self, e):
    e.accept()

def dragMoveEvent(self, e):
    e.accept()

def dropEvent(self, event):
    if event.source() == self:
        index = self.indexAt(event.pos())
        if not index.isValid():
            event.accept()
            return
        start_index = int(event.mimeData().data("index"))
        if start_index != index.row():
            print ("dropEvent called from row {} on row {}".format(start_index, index.row()))
            self.moveRow.emit(start_index, index.row())

        event.accept()