[FIXED] I'm using a class related to the Qtable widget but it doesn't show up in QMainWindow

Issue

I can't show DataEntryForm class in App class, ie inside QMainWindow. thank you so much.

#QWidget, The widget containing the QTableWidget I want to show

class DataEntryForm(QWidget):
    def __int__(self):
        super().__init__()

        self.item = 0
        self.data = {"Phone L": 50.5}

        # leftside
        self.table = QTableWidget()
        self.table.setColumnCount(2)
        self.table.setHorizontalHeaderLabels('Descriptions', 'Price')
        self.table.horizontalHeader().setSectionResizeMode(QHeaderView.Stretch)

        self.layout = QHBoxLayout()
        self.layout.addWidget(self.table, 50)
        self.setLayout(self.layout)

#QMainWindow, I want to show the Data Entry Form class in this class.

class App(QMainWindow):
    def __init__(self, widget):
        super().__init__()
        self.title = 'Hello, world!'
        self.setWindowTitle(self.title)
        self.resize(1200, 600)
        self.menuBar = self.menuBar()
        self.fileMenu = self.menuBar.addMenu('File')

        # export to csv file action
        exportAction = QAction('Export to csv', self)
        exportAction.setShortcut('Ctrl+E')

        self.setWindowIcon(QIcon('data-analysis_icon-icons.com_52842.ico'))
        # exportAction.triggered.connect

        # exit Action
        exitAction = QAction('Exit', self)
        exitAction.setShortcut("Ctrl+Q")
        exitAction.triggered.connect(lambda: app.quit())

        self.fileMenu.addAction(exportAction)
        self.fileMenu.addAction(exitAction)





if __name__ == '__main__':
    app = QApplication(sys.argv)
    x = DataEntryForm()
    ex = App(x)
    ex.show()
    sys.exit(app.exec_())

Solution

QMainWindow is a special type of QWidget that uses a central widget that shows its main content. While you're correctly creating an instance of your DataEntryForm, you're just adding that as an argument in the main window constructor, but you're doing nothing with it.

In order to use that widget, use setCentralWidget():

class App(QMainWindow):
    def __init__(self, widget):
        super().__init__()
        self.setCentralWidget(widget)
        # ...

_{Tip: avoid similar names for classes and instances of different types; app is an instance of a QApplication, App is a QMainWindow class. Use something different and more related for that class, like "MainWindow".}

Answered By - musicamante