QStackedLayout shows empty window for a few moments

Question

In this example, as the main window, I use a QWidget that contains a QStackedLayout and a QPushButton to change the current widget to a QStackedLayout.

from PySide6.QtWidgets import QFrame, QWidget, QApplication, QVBoxLayout, QStackedLayout, QPushButton
from PySide6.QtCore import Qt


class ColorWidget(QFrame):
    def __init__(self, color):
        super(ColorWidget, self).__init__()
        self.setFixedSize(200, 200)
        self.setStyleSheet(f"background-color: {color}; border-radius: 6px;")
        # Some widget. In this case, just a colored background.


class MainWidget(QWidget):
    def __init__(self):
        super(MainWidget, self).__init__()
        self.current_widget = False

        layout = QStackedLayout()
        layout.addWidget(ColorWidget("red"))
        layout.addWidget(ColorWidget("yellow"))
        layout.setCurrentIndex(0)

        self.setLayout(layout)
        # Main widget. Contains 2 colored widgets.

    def change_visible_widget(self):
        self.current_widget = not self.current_widget
        self.layout().setCurrentIndex(int(self.current_widget))


class MainWindow(QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.setWindowFlag(Qt.FramelessWindowHint)
        self.setAttribute(Qt.WA_TranslucentBackground)
        # no frame, no background

        layout = QVBoxLayout()

        main_widget = MainWidget()
        button = QPushButton("change")
        button.clicked.connect(main_widget.change_visible_widget)
        # button to change QStackedLayout index in Main Widget

        layout.addWidget(main_widget)
        layout.addWidget(button)
        self.setLayout(layout)


if __name__ == '__main__':
    app = QApplication()
    win = MainWindow()
    win.show()
    app.exec()

The problem is that when the program starts, an empty window appears for a few moments.

By trial and error, I realized that this is because of the QStackedLayout and the number of windows that appear is equal to the number of created QStackedLayout (in this case it is 1).

How can this be fixed?

Answer 1

Just add self to layout = QStackedLayout():

from PySide6.QtWidgets import QFrame, QWidget, QApplication, QVBoxLayout, QStackedLayout, QPushButton
from PySide6.QtCore import Qt


class ColorWidget(QFrame):
    def __init__(self, color):
        super(ColorWidget, self).__init__()
        self.setFixedSize(200, 200)
        
        self.setStyleSheet(f"background-color: {color}; border-radius: 6px;")
        # Some widget. In this case, just a colored background.


class MainWidget(QWidget):
    def __init__(self):
        super(MainWidget, self).__init__()
        self.current_widget = False

        layout = QStackedLayout(self)
        layout.addWidget(ColorWidget("red"))
        layout.addWidget(ColorWidget("yellow"))
        layout.setCurrentIndex(0)
        
        # Main widget. Contains 2 colored widgets.

    def change_visible_widget(self):
        self.current_widget = not self.current_widget
        self.layout().setCurrentIndex(int(self.current_widget))


class MainWindow(QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.setWindowFlag(Qt.FramelessWindowHint)
        self.setAttribute(Qt.WA_TranslucentBackground)
        # no frame, no background

        layout = QVBoxLayout()
        main_widget = MainWidget()
        button = QPushButton("change")
        button.clicked.connect(main_widget.change_visible_widget)
        # button to change QStackedLayout index in Main Widget

        layout.addWidget(main_widget)
        layout.addWidget(button)
        self.setLayout(layout)


if __name__ == '__main__':
    app = QApplication()
    win = MainWindow()
    win.show()
    app.exec()