I have a QListWidget which is populated by QLabel via .setItemWidget() and a drag and drop mode InternalMove, when I move an item inside the list its label disappears.
How can I solve this issue?
A minimal example to reproduce
from PyQt5.QtWidgets import (
QApplication, QLabel, QStyle,
QListWidget, QListWidgetItem
)
from PyQt5.QtCore import QSize
import sys
if __name__ == '__main__':
app = QApplication(sys.argv)
list = QListWidget()
list.setFixedHeight(400)
list.setDragDropMode(QListWidget.DragDropMode.InternalMove)
for _ in range(8):
item = QListWidgetItem()
item.setSizeHint(QSize(40, 40))
list.addItem(item)
label = QLabel()
label.setPixmap(list.style().standardIcon(
QStyle.StandardPixmap.SP_ArrowUp).pixmap(QSize(40,40)))
list.setItemWidget(item, label)
list.show()
sys.exit(app.exec())
edit
After reading the documentation for the .setItemWidget() which states:
This function should only be used to display static content in the place of a list widget item. If you want to display custom dynamic content or implement a custom editor widget, use QListView and subclass QStyledItemDelegate instead.
I wonder if this is related to the issue and what does "static content" mean in this context, is QLabel considered "dynamic content"?
edit #2
The problem is inside a dropEvent() a dropMimeData() is called which in turn creates a complete new item? (rowsInserted is called), which isn't supposed to happen for self items I guess, because a widget set in the dragged item isn't serialized and stored inside mimedata so the widget is decoupled, The dropMimeData() is usually called when you drag and drop items from a different list.
So I guess an ugly way to solve this is to store a manually serialized widget inside a QListWidget.mimeData() as a custom mimetype via QMimeData.setData() and recreate the widget after a drop inside QListWidget.dropMimeData().
for example:
from PyQt5.QtWidgets import (
QApplication, QLabel, QStyle,
QListWidget, QListWidgetItem
)
from PyQt5.QtCore import QSize, QMimeData, QBuffer, QIODevice
from PyQt5.QtGui import QPixmap
import pickle
import sys
class ListWidget(QListWidget):
def mimeData(self, items:list[QListWidgetItem]) -> QMimeData:
mimedata = QListWidget.mimeData(self, items)
# e.g. serialize pixmap
custommime = []
for item in items:
label:QLabel = self.itemWidget(item)
buff = QBuffer()
buff.open(QIODevice.OpenModeFlag.WriteOnly)
label.pixmap().save(buff, 'PNG')
buff.close()
custommime.append(buff.data())
mimedata.setData('application/custommime', pickle.dumps(custommime))
#
return mimedata
def dropMimeData(self, index:int, mimedata:QMimeData, action) -> bool:
result = QListWidget.dropMimeData(self, index, mimedata, action)
# e.g. recreate pixmap
if mimedata.hasFormat('application/custommime'):
for i, data in enumerate(
pickle.loads(mimedata.data('application/custommime')),
start=index):
pixmap = QPixmap()
pixmap.loadFromData(data, 'PNG')
label = QLabel()
label.setPixmap(pixmap)
self.setItemWidget(self.item(i), label)
#
return result
if __name__ == '__main__':
app = QApplication(sys.argv)
list = ListWidget()
list.setFixedHeight(400)
list.setDragDropMode(QListWidget.DragDropMode.InternalMove)
list.setSelectionMode(QListWidget.SelectionMode.ExtendedSelection)
for i in range(8):
item = QListWidgetItem()
item.setSizeHint(QSize(40, 40))
list.addItem(item)
label = QLabel()
label.setPixmap(list.style().standardIcon(
QStyle.StandardPixmap.SP_DialogOkButton + i).pixmap(QSize(40,40)))
list.setItemWidget(item, label)
list.show()
sys.exit(app.exec())
