need help about QlistWidget.data() problem(crashed without noticed)

[SGaist]

@Daniel-Breeze this is a first step but still not runnable, neither form.ui is available nor any of the other imported custom classes.

[Daniel Breeze]

@SGaist
thx, I wirte a simple version. this time well be easy to read

# This Python file uses the following encoding: utf-8
import sys

from PySide6.QtCore import Qt
from PySide6.QtWidgets import QApplication, QMainWindow, QListWidgetItem

# Important:
# You need to run the following command to generate the ui_form.py file
#     pyside6-uic form.ui -o ui_form.py, or
#     pyside2-uic form.ui -o ui_form.py
from ui_form import Ui_MainWindow

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

        item1 = QListWidgetItem("task 1")
        item2 = QListWidgetItem("task 2")

        self.ui.listWidget.addItem(item1)
        self.ui.listWidget.addItem(item2)

        action_data_list: List[QListWidgetItem] = []
        action_data_list_2: List[QListWidgetItem] = []
        action_data_list.append(QListWidgetItem("action 1"))
        action_data_list.append(QListWidgetItem("action 2"))

        self.ui.listWidget_2.addItem(action_data_list[0])
        self.ui.listWidget_2.addItem(action_data_list[1])

        item1.setData(Qt.UserRole, action_data_list)
        item2.setData(Qt.UserRole, action_data_list_2)

        self.ui.listWidget.itemClicked.connect(self.reload)

    # reload item to listWidget_2
    def reload(self):
        current_item = self.ui.listWidget.currentItem()
        action_data_list = current_item.data(Qt.UserRole)
        for i in range(self.ui.listWidget_2.count()):
            self.ui.listWidget_2.takeItem(0)
        self.ui.listWidget_2.clear()
        for action_data in action_data_list:
            self.ui.listWidget_2.addItem(action_data)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    widget = MainWindow()
    widget.show()
    sys.exit(app.exec())

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>800</width>
    <height>600</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <widget class="QListWidget" name="listWidget">
    <property name="geometry">
     <rect>
      <x>110</x>
      <y>170</y>
      <width>256</width>
      <height>192</height>
     </rect>
    </property>
   </widget>
   <widget class="QListWidget" name="listWidget_2">
    <property name="geometry">
     <rect>
      <x>440</x>
      <y>170</y>
      <width>256</width>
      <height>192</height>
     </rect>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menubar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>800</width>
     <height>21</height>
    </rect>
   </property>
  </widget>
  <widget class="QStatusBar" name="statusbar"/>
 </widget>
 <resources/>
 <connections/>
</ui>

[JonB]

@Daniel-Breeze
I have pasted your code into my Qt 15/PySide 2. It now looks like this:

So what is the issue/supposed to go wrong? I can click any item, if I click in left-hand list then right-hand list changes, nothing goes wrong. Is that all I am supposed to do? Does it go wrong for you in PySide6?

[Daniel Breeze]

@JonB
I try run it at pyside2. it work.

but pyside6 still crashed.
when you select task 2 the right list well empty. then you select task 1 the action 1 and action 2 should be restore at right list. in pyside6 had crashed, but pyside2 work fine.
and I changed a few version of pysidee6 it also crashed, is that pyside6 bug?
JonB would you please try it in pyside6, I really wanna know whats going on here

[JonB]

@Daniel-Breeze
If I had PySide 6 you can be sure I would have tried it :) That's why I tried PySide 2. Yes, whatever it is must be a PySide 6 issue.

[SGaist]

@Daniel-Breeze I would say that what you are doing is wrong. Your action_data_list contains QListWidgetItem objects. Objects that you remove and add to your other view. When you call takeItem, you "extract" the item from the view and thus become responsible for its lifetime management again (thus your call to clean are technically useless). Since you don't do anything with them, they get garbage collected, so next time you try to make use of them, you in fact will be using delete objects hence your crash.

One could wonder why the fact they are stored as custom data in listWidget items does not keep the reference, that might be the central point.

Anyway, since your items only contain strings, you should rather store a list of them as UserRole data and you can them simply call clean on your QListWidget objects. Then use addItems with the string list to recreate the content of listWidget_2.

[Daniel Breeze]

@SGaist
thx, I just Simplified my code here it is I didn't call any of remove item function when you select that item the program well direct crash.

# This Python file uses the following encoding: utf-8
import sys

from PySide6.QtCore import Qt
import PySide6.QtCore
from PySide6.QtWidgets import QApplication, QMainWindow, QListWidgetItem

# Important:
# You need to run the following command to generate the ui_form.py file
#     pyside6-uic form.ui -o ui_form.py, or
#     pyside2-uic form.ui -o ui_form.py
from ui_form import Ui_MainWindow

class MainWindow(QMainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)

        print(PySide6.QtCore.__version__)

        self._previous_item = None

        item1 = QListWidgetItem("task 1")

        self.ui.listWidget.addItem(item1)

        action_data_list: list[QListWidgetItem] = []
        action_data_list.append(QListWidgetItem("action 1"))
        action_data_list.append(QListWidgetItem("action 2"))

        item1.setData(Qt.UserRole, action_data_list)

        self.ui.listWidget.itemClicked.connect(self.reload)

    # reload item to listWidget_2
    def reload(self):
        action_data_list = self.ui.listWidget.item(0).data(Qt.UserRole)
        for action_data in action_data_list:
            self.ui.listWidget_2.addItem(action_data)

if __name__ == "__main__":
    app = QApplication(sys.argv)
    widget = MainWindow()
    widget.show()
    sys.exit(app.exec())

you mean when init function after excuted, the action_data_list are already deleted?

[jsulm]

@Daniel-Breeze said in need help about QlistWidget.data() problem(crashed without noticed):

the program well direct crash

Where exactly? What does debugger say?

[Daniel Breeze]

@jsulm

debugger say nothing
u can create window UI project choose pyside6 and mainwindow, add a listwidget in UI designer, copy my last code in your mainwindow.py run program click task 1. then program crash

I think the problem is .data(Qt.UserRole) , if I # it. every seem okay

[JonB]

@Daniel-Breeze
The following is what I would try if I wanted either to find a workaround or report as a PySide6 bug:

• Move the self.ui.listWidget.addItem(item1) to after the item1.setData(Qt.UserRole, action_data_list). It should make no difference, but just in case.
• Put print() statements into def reload(). Does it "die" on action_data_list = self.ui.listWidget.item(0).data(Qt.UserRole) or on the for action_data in action_data_list?
• Make sure self.ui.listWidget.item(0) on its own accesses the item without "dying".
• Change Qt.UserRole to Qt.DisplayRole (forget about your action_data_list), make sure that works.
• Try using Qt.UserRole + 100 just in case.
• You are marshalling a Python list, and a list of QListWidgetItem at that, across Qt QVariant (data()) boundaries. Try (a) just a plain string/number then (b) a simple Python list of strings/numbers. Do either of those work OK?
• If (b) works, as your code stands you do not need to store QListWidgetItems (and worry about their possible ownership), you might as well just store strings.

Those are a start :)

[SGaist]

@jsulm It's not a python crash, it's a C++ crash.

It happens because the application tries to access already freed resources.

On the technical side, I think that there's something that might be off with Python/C++ memory management at play. Technically, the items are stored in a temporary list which itself is then stored in an item. That should make it not temporary anymore and thus keep a reference to the items. However, it looks like it does not work that way. It might be due to the nature of the objects stored there.

That said, the simple fix in this case is to use a list of strings rather than a list of QListWidgetItem. You can then leverage the addItems function so you have one less loop in your code.