Dynamic theme changing in PyQt application - pyqt5

Question

I need to develop a dynamic theme changing in PyQt application, I have different components, and depending on the theme I need to change styles. I need to change the theme from some specific component and all components should change their styles. I do not use global styles, I need to write styles for each component separately in its class.
At the moment I came up with such an implementation:
I grab GlobalObject class from this article - https://stackoverflow.com/a/55554690/15709458.
And for each component, I put a listener for the "themeChanged" event. And by dispatching this event, I notify all components which listen to this event that the theme of the application has changed.
Dispatching event example:
def set_dark_theme(app: QApplication):
app.setProperty("theme", "dark")
GlobalObject().dispatchEvent("themeChanged")
Component example:
class CheckBox(QCheckBox):
def __init__(self, parent=None):
super().__init__(parent)
self.update_stylesheet()
GlobalObject().addEventListener("themeChanged", self.update_stylesheet)
def update_stylesheet(self):
theme = QApplication.instance().property("theme")
if theme == "dark":
text_color = __colors__["gray"][200]
else:
text_color = __colors__["gray"][700]
self.setStyleSheet(
f"QCheckBox {{ spacing: 8px; font-size: 14px; font-weight: 500; color: {text_color}; }}"
)
Will such an implementation adversely affect performance due to the fact that all components in the application of which there can be a lot will be subscribed to the event? Is it possible to somehow improve this solution, for example using some built-in methods?

Answer 1

You do not have to use events at all!
You can simply have a QWidget as main class which holds all the other widgets. Then you can use setStyleSheet() once and the appearance will change for all widgets as long as they are in the stylesheet or inherit from a class in the stylesheet.
If you set a style for QWidget for example, the properties will be set for almost all widgets as they all inherit from QWidget.
You can see the minimal example below for reference. Click the CheckBox and the style will change to dark.
import sys
from PyQt5 import QtWidgets, QtGui
class Window(QtWidgets.QWidget):
def __init__(self, parent=None):
super().__init__(parent)
self.checkbox = QtWidgets.QCheckBox(self)
self.checkbox.toggled.connect(self.change_theme)
def change_theme(self):
if theme == "dark":
text_color = __colors__["gray"][200]
else:
text_color = __colors__["gray"][700]
self.setStyleSheet("QWidget { background-color: black; color: white; } QCheckBox { spacing: 8px; font-size: 14px; font-weight: 500; color: {text_color}; background-color: grey; }")
app = QtWidgets.QApplication(sys.argv)
main = Window()
main.show()
sys.exit(app.exec_())
Edit: I added the theme color variables