auto parent bugs

[hannesdelbeke]

auto parent widget is causing a lot of issues
consider disabling by default? and provide instructions to devs how to parent their widgets.

• Under Blender 4.3, getting an error with orphan_widgets #125
• causes parent bug on buttonizer #114
• auto parent bug #113
• auto dock windows option #90
• bqt attempts to parent dropdown list to blender window #86
• auto parent widgets without parent #71

there are also pros

• https://blenderartists.org/t/bqt-custom-ui-for-add-ons-tool-in-blender-with-pyqt-or-pyside/1458808/12?u=h4nnes
  

[Jerakin]

When auto parenting where implemented what where it trying to solve? Was it that creating a window and opening it will close it immediately if it doesn't have a parent?

[hannesdelbeke]

I enabled auto parenting

• to prevent widgets from being destroyed / instantly garbage collected.
• to be parented to the main window so that you don't alt tab between multiple qt windows
• to avoid the need to create a custom wrapper around pre-existing qt or Python tools
• so qt just works, so a developer doesn't has to learn the bqt API

I tried to make the whole system smarter and easier for developer. But it feels like it made it more complex and introduced more bugs

[hannesdelbeke]

@Jerakin what is your experience with auto parenting? do you keep it enabled?
interested since it sounds like you are using it in a studio so I assume you have multiple users, which gives a broad testing range for user experience

[Jerakin]

We only set BQT_DOCKABLE_WRAP = "0"

Which means that auto parenting is enabled but it doesn't surface all small controllers that doesn't have a parent.

[Jerakin]

I have to look into how PySide behaves in other dccs, like does Maya do something similar to this under the hood?

• to prevent widgets from being destroyed / instantly garbage collected.
  • A widget without a parent is expected to be garbage collected, but maybe other dccs prevents that?
  • Thinking about this, I would think that a widget without a parent would be garbage collected but not so sure with a window/dialog.
• to be parented to the main window so that you don't alt tab between multiple qt windows
  • This is a nice feature, wonder if this happens implicitly in other dccs too or if you have to set the parent.
• to avoid the need to create a custom wrapper around pre-existing qt or Python tools
  • If bqt have to create some wrappers I think that's fine, but bqt should be transparent to users. In my "perfect" world we shouldn't have to import bqt in a script. ¹
• so qt just works, so a developer doesn't has to learn the bqt API
  • Yeah, this is high prio for me. A user should have to interact minimally with bqt.

---

¹ - I think an easy way to get the parent window and use that is not too bad. We have to get the maya main window in odd ways when doing things sometimes.

[hannesdelbeke]

Some dccs or IDEs i used in past, parent to the main qapp if parent is none. So you can just do

# pseudocode
Mybtn=qwidget.qbutton()
Mybtn.show()

It made developing quite easy, but then every time i devd in maya it broke using same approach. So i might v just learned bad habbits.

most dccs max maya need a proper parent to support parenting to the main window, and dockable support etc. so it's likely not a best practice

[Jerakin]

Yeah I double checked in maya and it behaves like bqt behaves without auto parenting on.

Too me it feels BQT_DOCKABLE_WRAP and BQT_AUTO_ADD are encouraging some bad practices. It's a little bit "too much magic" for me. The thinking and intent is noble, making it easier for the user. But it mutates/wraps widgets unexpectedly and as we have seen introduces a lot of unexpected behaviors.

I don't think it's too much to ask that people properly set parents like PySide expects, or to wrap their widgets in Dockables if they want them to dock.

I think that we should probably clean this up for the next major release and, as you say in your initial post, change the default behavior to be in line with standard PySide.

[hannesdelbeke]

A user should have to interact minimally with bqt.

This was my main aim. But:

• To not interact with bqt, we avoid import bqt, and auto parent
• if w auto parent, we also sometimes auto parent e.g. list items. It's a race condition i think, parenting before parent relationship is properly established. I avoided this by filtering the exception widgets based on their type. But it's a hack not a neat solution. List items are fixed now, but some other random widgets sometimes might still do this.

avoiding importing bqt is a restriction i put on myself with the aim to make qt dev easier.
But after using it for years, i think the implicit issues it introduced from automatic smart parenting is a worse dev experience for most users, than informing the user in the docs to import bqt and explicitly parent correctly.

[Jerakin]

I wrote this for testing how it behaves under different circumstances that would also work when testing in other dcs.

Requires this patch to track the parented widgets
git apply track-parented.patch
track-parented.patch

import os

from PySide6 import QtWidgets, QtCore

try:
    from bqt.manager import _parented_widgets
except ImportError:
    _parented_widgets = []

import time

def findMainWindow() -> QtWidgets.QMainWindow | None:
    app = QtWidgets.QApplication.instance()
    for widget in app.topLevelWidgets():
        if isinstance(widget, QtWidgets.QMainWindow):
            return widget
    return None


class MyWidget(QtWidgets.QDialog):
    def __init__(self, parent):
        super(MyWidget, self).__init__(parent=parent)

        self.timer = QtCore.QTimer()
        self.timer.setInterval(500)
        self.timer.timeout.connect(self.update_lbl)
        self.timer.start()

        self.setLayout(QtWidgets.QVBoxLayout())

        self.layout().addWidget(QtWidgets.QLabel("-- Settings --"))

        self.auto_add = QtWidgets.QCheckBox("Auto Add")
        self.auto_add.stateChanged.connect(lambda x: self.set_state("BQT_AUTO_ADD", x))
        self.auto_add.setChecked(True if os.environ.get("BQT_AUTO_ADD", "1") == "1" else False)
        self.layout().addWidget(self.auto_add)

        self.dockable_wrap = QtWidgets.QCheckBox("Dockable Wrap")
        self.dockable_wrap.stateChanged.connect(lambda x: self.set_state("BQT_DOCKABLE_WRAP", x))
        self.dockable_wrap.setChecked(True if os.environ.get("BQT_DOCKABLE_WRAP", "0") == "1" else False)
        self.layout().addWidget(self.dockable_wrap)

        self.layout().addWidget(QtWidgets.QLabel("-- Dialog test --"))

        self.dialog_parent = QtWidgets.QCheckBox("Parent Dialog")
        self.layout().addWidget(self.dialog_parent)

        self.dialog_button = QtWidgets.QPushButton("Dialog")
        self.dialog_button.clicked.connect(self.dialog)
        self.layout().addWidget(self.dialog_button)

        self.layout().addWidget(QtWidgets.QLabel("-- Label Tests --"))

        self.add_label_button = QtWidgets.QPushButton("Add Label")
        self.add_label_button.clicked.connect(self.add_label)
        self.layout().addWidget(self.add_label_button)

        self.clear_labels_button = QtWidgets.QPushButton("Clear Labels")
        self.clear_labels_button.clicked.connect(self.clear_labels)
        self.layout().addWidget(self.clear_labels_button)

        self.clear_labels_delay_button = QtWidgets.QPushButton("Clear Labels with delay")
        self.clear_labels_delay_button.clicked.connect(lambda: self.clear_labels(True))
        self.layout().addWidget(self.clear_labels_delay_button)

        self.layout_with_dynamic_items = QtWidgets.QVBoxLayout()
        self.layout().addLayout(self.layout_with_dynamic_items)

        self.layout().addWidget(QtWidgets.QLabel("-- INFO --"))
        self.parented_widgets_lbl = QtWidgets.QLabel("Parented Widgets: ?")

    def dialog(self):
        parent = None
        if self.dialog_parent.isChecked():
            parent = self
        dlg = QtWidgets.QDialog(parent)
        dlg.setWindowTitle("HELLO!")
        dlg.exec()

    def update_lbl(self):
        self.parented_widgets_lbl.setText("Parented Widgets: " + str(len(_parented_widgets)))

    def set_state(self, var, state):
        os.environ[var] = "1" if state else "0"

    def add_label(self):
        for i in range(5):
            new_label = QtWidgets.QLabel("label")
            self.layout_with_dynamic_items.addWidget(new_label)

    def clear_labels(self, delay=False):
        for i in reversed(range(self.layout_with_dynamic_items.count())):
            item = self.layout_with_dynamic_items.takeAt(i)
            widget = item.widget()
            widget.setParent(None)
            widget.deleteLater()

        # -- Run any code that causes a bit of a delay - which means that
        # -- bqt will attempt to parent orphan widgets before Qt has managed
        # -- to delete the widgets
        if delay:
            time.sleep(2)

class MyWindow(QtWidgets.QMainWindow):
    def __init__(self, parent):
        super(MyWindow, self).__init__(parent=parent)

        self.widget = MyWidget(parent)
        self.setCentralWidget(self.widget)


def launch():
    window = findMainWindow()
    print("found main window", window)
    w = MyWindow(window)
    w.show()

launch()

[hannesdelbeke]

Is this like a unit test you manually run to test parenting behavior in bqt?

[Jerakin]

Just an app I run inside Blender where I can set the global vars, and see how it behaves under different circumstances (removing widgets, spawning dialogs)

[hannesdelbeke]

Yeah I double checked in maya and it behaves like bqt behaves without auto parenting on.

Too me it feels BQT_DOCKABLE_WRAP and BQT_AUTO_ADD are encouraging some bad practices. It's a little bit "too much magic" for me. The thinking and intent is noble, making it easier for the user. But it mutates/wraps widgets unexpectedly and as we have seen introduces a lot of unexpected behaviors.

I don't think it's too much to ask that people properly set parents like PySide expects, or to wrap their widgets in Dockables if they want them to dock.

I think that we should probably clean this up for the next major release and, as you say in your initial post, change the default behavior to be in line with standard PySide.

I agree