How to modify drop event in QListView

Question

I have a QListView where items can be reordered with drag-and-drop by setting dragDropMode to DragDrop and defaultDropAction to MoveAction. How can I intercept the drop event, to find out what is trying to be moved where in relation to the rest of the list, so that I can cancel this action under certain conditions? E.g. I want to forbid moving some items behind other.

Answer 1

You can access the indexes and items involved in the dropEvent and setDropAction to Qt.IgnoreAction to cancel the drop depending on your criteria. Since you weren't specific, for this demonstration I just created one item that stays at the bottom.

import sys
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *

class List(QListView):

    def dropEvent(self, event):
        i = self.selectedIndexes()[0]
        j = self.indexAt(event.pos())

        # To access the items involved
        source = self.model().itemFromIndex(i)
        target = self.model().itemFromIndex(j)

        bottom = (self.model().rowCount() - 1, -1)
        if i.row() in bottom or j.row() in bottom:
            event.setDropAction(Qt.IgnoreAction)
        else:
            super().dropEvent(event)


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = QWidget()
    lv = List()
    lv.setDragDropMode(QAbstractItemView.DragDrop)
    lv.setDefaultDropAction(Qt.MoveAction)
    
    model = QStandardItemModel(5, 1)
    for i in range(4):
        item = QStandardItem(f'Item {i + 1}')
        item.setFlags(item.flags() & ~Qt.ItemIsDropEnabled)
        model.setItem(i, 0, item)    
    item = QStandardItem('I stay at the bottom ._.')
    model.setItem(4, 0, item)
    lv.setModel(model)
    
    vbox = QVBoxLayout(window)
    vbox.addWidget(lv)
    window.show()
    sys.exit(app.exec_())