PyQt5 - Switch between two QMainWindow with stacked widget

Bored Nerd

when the user clicks the button "PLAY" of the window1, the button calls the function "playgame" which basically invokes the class of the window2 and is added on the stacked widget , but every time I click the button, the program crashes without displaying any specific error in the terminal.
Is there any solution ?

NOTE : both files are generated by qt designer, I converted them to
py and I added some changes

window1.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'game_flag.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.

from PyQt5 import QtCore, QtWidgets
import sys
from window2 import gameart

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(889, 680)
        MainWindow.setStyleSheet("background-color : #161219;")
        MainWindow.setWindowFlags(QtCore.Qt.FramelessWindowHint)

        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")

        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(260, 300, 381, 141))
        self.pushButton.setStyleSheet("QPushButton{\n"
        "    border: 4px  groove #BC006C;\n"
        "    border-radius: 20px;\n"
        "    color:white;\n"
        "    font: 20pt \"Lexend SemiBold\";\n"
        "}\n"
        "QPushButton:hover{\n"
        "    background-color : #800048;\n"
        "    \n"
        "}\n"
        "")
        self.pushButton.setObjectName("pushButton")
        self.pushButton.clicked.connect(self.playgame) #when clicked, calls the function playgame
        MainWindow.setCentralWidget(self.centralwidget)
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)
    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "PLAY"))
    def playgame(self): #call the mainwindow of window2
        secondwindow = gameart().start()
        widget.addWidget(secondwindow)
        widget.setCurrentIndex(secondwindow)
class gameintro():
    def __init__(self):
        app = QtWidgets.QApplication(sys.argv)
        MainWindow = QtWidgets.QMainWindow()
        ui = Ui_MainWindow()
        ui.setupUi(MainWindow)
        MainWindow.show()
        sys.exit(app.exec_())

if __name__ == "__main__":
    firstwindow = gameintro()
    widget = QtWidgets.QStackedWidget()
    widget.addWidget(firstwindow) #add the mainwindow of window1 to the stackwidget
    widget.setCurrentIndex(firstwindow)

window2.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'game_flag.ui'
#
# Created by: PyQt5 UI code generator 5.15.4
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtWidgets
import sys



class Ui_MainWindow(object):

    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(889, 680)
        MainWindow.setStyleSheet("background-color : #161219;")
        MainWindow.setWindowFlags(QtCore.Qt.FramelessWindowHint)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        MainWindow.setCentralWidget(self.centralwidget)
        self.centralwidget.setObjectName("centralwidget")
        QtCore.QMetaObject.connectSlotsByName(MainWindow)
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(260, 300, 381, 141))
        self.pushButton.setStyleSheet("QPushButton{\n"
                                      "    border: 4px  groove #BC006C;\n"
                                      "    border-radius: 20px;\n"
                                      "    color:white;\n"
                                      "    font: 20pt \"Lexend SemiBold\";\n"
                                      "}\n"
                                      "QPushButton:hover{\n"
                                      "    background-color : #800048;\n"
                                      "    \n"
                                      "}\n"
                                      "")
        self.pushButton.setObjectName("pushButton")
        self.retranslateUi(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle("Country Game")
        self.pushButton.setText(_translate("MainWindow", "TEST"))

class gameart():
    def start(self):
        app = QtWidgets.QApplication(sys.argv)
        MainWindow = QtWidgets.QMainWindow()
        ui = Ui_MainWindow()
        ui.setupUi(MainWindow)
        MainWindow.show()
        app.exec_()

JonB

@Bored-Nerd said in PyQt5 - Switch between two QMainWindow with stacked widget:

but every time I click the button, the program crashes without displaying any specific error in the terminal.

I don't know what you are doing with multiple main windows, stacked widgets and so on. But your window1.py creates a QApplication in gameintro.__init__() and your window2.py has a gameart.start() which you call and that also creates a QApplication. Which for sure is wrong (you can only have one instance of a QApplication), and will crash or otherwise misbehave.

I would not hazard to tell you what you should do as I do not follow any of your logic.

BTW, the only thing that makes sense would be to have one QMainWindow in your application. That could contain a QStackedWidget which you use to display alternative content in that main window.

Bored Nerd

@JonB
these 2 files are the simplified version of the 2 original files which they contains a lot of code that has nothing to do with the problem .
My logic here is : once the user clicks the button "Play" , stacked widget adds the mainwindow of window2 and set its index and the mainwindow of the window2 will be display to the user.
About your last comment, is it possible to have one QMainWindow with 2 classes? I tried implementing it but it crashes

JonB

@Bored-Nerd
Since this is not your actual code it is not possible to comment on why it crashes. Your "simplified" code contains two places where you create a QApplication, and if you have that it is wrong. And you have secondwindow = gameart().start(), which does not even return a value, and certainly not a window. In itself having multiple QMainWindows would not crash.

Bored Nerd

Yes, in the 2 original files there are 2 QApplication, but still crashes even though I deleted the QApplication of window2

SGaist

Hi,

You can have as many QMainWindow as you want, it just does not make much sense.

As for your design, the main issue is that your gameart and gameintro class/function do mostly the same thing so at some point you are creating two instances of QApplication which is wrong.

You should clean that logic first. Also, there is no need for classes for such functions.

JonB

@Bored-Nerd
What would you like us to say? We cannot tell you why what crashes when you freely admit this is not your actual code.

In any case, you need to redesign your code from anything like what it is now for it to make sense.

Bored Nerd

@JonB Like I said before, these 2 files are the "simplified" version of the 2 original files. I'm testing with stackedwidget but it doesn't work. It doesn't make any difference if I upload the whole code. I am here because I am trying to figure out if it's possible to use stackedwidget with 2 QMainWindow (and if it makes sense or not) and from what I understood there must be one QApplication and QMainWindow.

SGaist

No, as already written, you can have as many QMainWindow you want.

QApplication must be unique.

It does not really make sense to use several QMainWindow in a given application but that is up to you.

Did you try to run your application with gdb to find exactly where it crashes ?

You might also want to do some testing with widgets built only in code rather than with designer.

JonB

@Bored-Nerd
Yes it is possible to have a QStackedWidget which alternates between two QMainWindows if that is what you want.

You would have a main program, with a single QApplicaton, and with the QStackedWidget. There you should create the two separate QMainWindow instances and put them both into the QStackedWidget. Only the first will be shown at this point. Upon pressing a button in one of these, the stacked widget should change its index to show the other QMainWindow instance. Then your issue is that the button press signal in either QMainWindow should have its slot where the QStackedWidget is so that can change the active index for which main window to show.