PyQt5 – Detecting When Other Window Closes

I’m using PyQt5 and I need to have my main window detect when a different window closes. I read here Emit a signal from another class to main class that creating a signal class to serve as an intermediary should work. However I haven’t gotten my example to work.

In my example, clicking the button opens a QWidget window. When the QWidget is closed, the main window is supposed to change from a blue background to a red background. However, the main window remains blue using the script below.

What am I doing wrong?

from PyQt5.QtWidgets import QPushButton
from PyQt5.QtCore import QObject, pyqtSignal
import os, sys

class MySignal(QObject):
    signal = pyqtSignal()

class MyMainWindow(QMainWindow):

    def __init__(self):
        super().__init__()
        
        #Make mainwindow
        self.setGeometry(100,100,300,200)
        self.setStyleSheet('background-color: blue')
        
        # Make widget and button objects and set connection
        self.widget = MyWidget()        
        self.btn = QPushButton(self)
        self.btn.setText('Click')
        self.btn.move(175, 150)
        self.btn.setStyleSheet('background-color: white')
        self.btn.clicked.connect(self.widget.showWidget)
        
        # Make signal object and set connection
        self.mySignal = MySignal()
        self.mySignal.signal.connect(self.changeToRed)
        
        # Let's start
        self.show()
        
    def changeToRed(self):
        self.setStyleSheet('background-color: red')
        
    def closeEvent(self, event):
        os._exit(0)
        
class MyWidget(QWidget):
    def __init__(self):
        super().__init__() 
        self.setGeometry(500, 100, 200, 200)
        self.sig = MySignal()
        
    def showWidget(self):
        self.show()
        
    def closeEvent(self, event):
        self.sig.signal.emit()
        self.close()
        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = MyMainWindow()
    app.exec()```

>Solution :

All you need is to add the connection between the close event and the function that turn your main screen red:

self.widget.closeEvent = self.changeToRed

this line should be in your main Window class

change your changeToRed function so it will except the event too:

def changeToRed(self, e):