[FIXED] PyQt5 button "clicked.connect()" not working when importing from class

Issue

I am running a test for clicked.connect failing issue.

I want to wrap all the widgets in the CentralWidget to a class called React. When I call React in CentralWidget, widgets like Button, self.writeLine and self.valLabel will show up, but when I pressed the react Button, it's not functioning, which is to update self.valLabel according to self.writeLine.

A snap shot: Buttom not working

I suspect that

Button.clicked.connect(self.BottomPressedTest) # no function when pressed

is not doing what is supposed to do. But have no clue why this is happening.

The entire test code is shown below,

from PyQt5 import QtCore, QtWidgets, QtGui
import sys


class CentralWidget(QtWidgets.QWidget):

    def __init__(self, parent=None):
        super(CentralWidget, self).__init__(parent)
        

        self.mainLayout = QtWidgets.QGridLayout()
        self.setLayout(self.mainLayout)

        panel = React(1).groupbox

        self.mainLayout.addWidget(panel, 0, 0)


class React(QtWidgets.QGroupBox):
    def __init__(self, ch):
        self.value = 0
        self.groupbox = QtWidgets.QGroupBox()

        self.vbox = QtWidgets.QVBoxLayout()
        self.groupbox.setLayout(self.vbox)

        Button = QtWidgets.QPushButton('React')
        Button.clicked.connect(self.BottomPressedTest) # no function when pressed

        self.writeLine = QtWidgets.QSpinBox()#QLineEdit()
        self.writeLine.setFont(QtGui.QFont('Arial', 16))

        self.valLabel = QtWidgets.QLabel()
        self.valLabel.setFont(QtGui.QFont('Arial', 20))
        self.valLabel.setText(f'React: {self.value}')

        self.vbox.addWidget(Button)
        self.vbox.addWidget(self.valLabel)
        self.vbox.addWidget(self.writeLine)

    def BottomPressedTest(self):
        print('React bottom pressed.')
        self.valLabel.setText(f'React: {self.writeLine.text()}')


class MainWindow(QtWidgets.QMainWindow):
    def __init__(self, parent=None):


        super(MainWindow, self).__init__(parent)

        self.setWindowTitle(QtCore.QCoreApplication.applicationName())

        self.centralWidget = CentralWidget()
        self.setCentralWidget(self.centralWidget)


class MainApplication(QtWidgets.QApplication):

    def __init__(self, argv: list):

        super(MainApplication, self).__init__(argv)
        self.mainWindow = MainWindow()
        self.mainWindow.resize(200,200) 
        self.mainWindow.raise_()
        self.mainWindow.show()

def main():

    application = MainApplication([])

    sys.exit(application.exec_())

if __name__ == "__main__":
    main()

Edit

I changed the first few line in React to

class React(QtWidgets.QGroupBox):
    def __init__(self, ch):
        super().__init__()
        self.value = 0
        self.setStyleSheet('QGroupBox { color: white; border: 3px solid grey; }') #

        self.vbox = QtWidgets.QVBoxLayout()
        self.setLayout(self.vbox)

, and then change CentralWidget to

class CentralWidget(QtWidgets.QWidget):

    def __init__(self, parent=None):
        super(CentralWidget, self).__init__(parent)
        

        self.mainLayout = QtWidgets.QGridLayout()
        self.setLayout(self.mainLayout)

        panel = React(1)
        self.mainLayout.addWidget(panel)

Now the problem is solved. Many thanks to @musicamante and @Passerby

Solution

Your React object is thrown away at the end of CentralWidget.__init__, with only the QGroupBox persisting. Save it in an attribute and your problem will be solved.

Note that your React object inherits from QGroupBox, but does not call its __init__ method, instead creating a new QGroupBox as a member.

Answered By - Passerby