如何拖放具有附加属性的QListWidgetItem子类的实例？

class CustomItem(QListWidgetItem):
    def __init__(self, text, additional_data):
        super().__init__(text)
        self.additional_data = additional_data

class SourceWidget(QListWidget):
    def __init__(self):
        super().__init__()
        self.setDragEnabled(True)

    def startDrag(self, supported_actions):
        item = self.currentItem()
        if item:
            data = QByteArray()
            stream = QDataStream(data, QIODevice.WriteOnly)
            stream << item.additional_data
            mime_data = QMimeData()
            mime_data.setData('application/custom-item', data)
            drag = QDrag(self)
            drag.setMimeData(mime_data)
            drag.exec_(supported_actions)

class TargetWidget(QListWidget):
    def __init__(self):
        super().__init__()
        self.setAcceptDrops(True)

    def dragEnterEvent(self, event):
        if event.mimeData().hasFormat('application/custom-item'):
            event.accept()
        else:
            event.ignore()

    def dropEvent(self, event):
        if event.mimeData().hasFormat('application/custom-item'):
            data = event.mimeData().data('application/custom-item')
            stream = QDataStream(data, QIODevice.ReadOnly)
            additional_data = None
            stream >> additional_data
            item = CustomItem('Dropped Item', additional_data)
            self.addItem(item)
            event.accept()
        else:
            event.ignore()