PySide6 Property notify signal emit automatically

Anonimista

I need clarification about PySide6 Property class. The documentation says

"The signal is emitted automatically when the property is changed via the Qt API ( setProperty , QMetaProperty , etc.), but not when the MEMBER is changed directly." here and here

I am unable to replicate what that sentence says in PySide6. For testing purposes I subclassed QLabel and added my class a property with a corresponding signal. But the signal is only emitted when I do it manually (ie. when I use self.bgColorChanged.emit()) whether I use setBgColor or setProperty.

So I either do not understand what the quoted sentence means or I'am doing something wrong in my code.

Here is the full code

import sys
import random

from PySide6.QtCore import Property, Signal
from PySide6.QtWidgets import (QApplication, 
    QWidget, QLabel, QPushButton, QVBoxLayout)


class StyledLabel(QLabel):
    
    _bg_color = 'lightgreen'
    bgColorChanged = Signal()
    
    def bgColor(self):
        return self._bg_color
    
    def setBgColor(self, bg_color):
        self._bg_color = bg_color
        self.setStyleSheet(
            f'StyledLabel {{ background-color: {self.bgColor}}}')
        # self.bgColorChanged.emit()
        
    bgColor = Property(
        str, 
        fget=bgColor, 
        fset=setBgColor, 
        notify=bgColorChanged)    


class Window(QWidget):
    
    colors = ['darkCyan', 'darkYellow', 'darkGrey',
              'cyan', 'yellow', 'gray', 'orange', 'teal']
    
    def __init__(self):

        super().__init__()
        
        layout = QVBoxLayout()
        self.setLayout(layout)
        
        button = QPushButton('Change label color')
        button.clicked.connect(self.on_button_clicked)
        layout.addWidget(button)

        self.label = StyledLabel('Label with style')
        self.label.setBgColor('lightsteelblue')
        self.label.bgColorChanged.connect(self.on_bgcolor_changed)
        layout.addWidget(self.label)
        
    def on_button_clicked(self):
        # self.label.setBgColor(random.choice(self.colors))
        self.label.setProperty('bgColor', random.choice(self.colors))
        
    def on_bgcolor_changed(self):
        print('Background color changed')


if __name__ == '__main__':

    if not QApplication.instance():
        app = QApplication(sys.argv)
    else:
        app = QApplication.instance()

    main_window = Window()
    main_window.show()

    sys.exit(app.exec())

SGaist

Hi,

As the example code shows in the document you link, the signal is emitted explicitly when a change occurs.
You have to code it yourself.

Anonimista

@SGaist Thank you