Coming back (after 2 years ! ) to close this out, since I finally have a solution that's held up in production.
Short answer: you can't get a real inline dropdown in Designer's Property Editor from pure Python. That specific bit needs a compiled C++ plugin. But there's a Python path that works well in practice — I'll explain both.
What doesn't work (so you can skip the dead-ends I hit):
I tried a QDesignerPropertySheetExtension to swap the property's editor. On PySide6 6.11:
You can't delegate to Designer's built-in sheet — extensionManager().extension(...) hands it back as a bare QObject and shiboken can't recover the real interface, so the methods just aren't there.
Replacing the sheet wholesale with a Python-built one segfaults Designer during form load — even when every property returns a plain string. Its core assumes the internal C++ sheet.
Also worth knowing: declaring the property as a Q_ENUM/@QEnum does give you a dropdown, but only for static, compile-time enums baked into the widget. It's no help if your options are computed at runtime (mine come from a project file), which was the whole point.
What actually works — a task-menu extension:
Right-click the widget → your action pops a combo box → you write the choice back through the form cursor. It's undo-aware, dirties the form, and saves to the .ui like any normal edit.
from PySide6.QtDesigner import (QExtensionFactory, QPyDesignerTaskMenuExtension,
QDesignerFormWindowInterface)
from PySide6.QtGui import QAction
from PySide6.QtWidgets import QInputDialog
TASKMENU_IID = "org.qt-project.Qt.Designer.TaskMenu"
class ThemeTaskMenu(QPyDesignerTaskMenuExtension):
def __init__(self, widget, parent=None):
super().__init__(parent)
self._widget = widget
self._action = QAction("Set theme…", self)
self._action.triggered.connect(self._choose)
def taskActions(self):
return [self._action]
def _choose(self):
names = ["Light", "Dark", "Solarized"] # build this list at runtime
current = self._widget.property("appTheme") or ""
i = names.index(current) if current in names else 0
name, ok = QInputDialog.getItem(self._widget.window(),
"Theme", "Theme:", names, i, False)
if not ok or not name:
return
fw = QDesignerFormWindowInterface.findFormWindow(self._widget)
# cursor path = undoable + saved to the .ui; a raw setProperty won't stick
(fw.cursor().setWidgetProperty(self._widget, "appTheme", name)
if fw else self._widget.setProperty("appTheme", name))
class ThemeTaskMenuFactory(QExtensionFactory):
def createExtension(self, obj, iid, parent):
if iid != TASKMENU_IID or not isinstance(obj, MyCustomWidget):
return None
return ThemeTaskMenu(obj, parent)
Register it in your plugin's initialize(core):
core.extensionManager().registerExtensions(
ThemeTaskMenuFactory(core.extensionManager()), TASKMENU_IID)
Two things that bit me:
Apply via fw.cursor().setWidgetProperty(...), not just widget.setProperty(...) — otherwise the change never makes it into the saved .ui.
Keep the underlying property a plain, validated @Property(str). The menu is only an input aid; the stored value stays portable and works fine on machines without your plugin.
If you have both PyQt5 and PySide6 installed, launch designer with QT_API=pyside6 or qtpy may pick PyQt5 and your plugin import will fail.
So: static enum → Q_ENUM. Runtime options → task-menu extension. True inline dropdown → C++ only.
I use a slightly fancier version of this (a little dock with a combo per property) in my widgets library if anyone wants a fuller reference:
https://github.com/SpinnCompany/QT-PyQt-PySide-Custom-Widgets
Marking this solved — hope it saves someone the segfault hunt.
