Problems using method in subclass dialog window to affect main window

Question

I'm trying to create a GUI program using PyQT5. I'm new to programming and Python so if I'm explaining things in the wrong way please correct me.

I have a main window that will contain multiple QLineEdit widgets and corresponding "Clear" buttons to clear the user entered data. The main window also contains "Edit" buttons to dispay specific dialog boxes where the data can also be edited. My example has a "User ID" QLineEdit widget/text box, "Clear" and "Edit" push buttons.

The dialog box that appears when "Edit' is clicked has it's own "Clear" button. If the Clear button in the dialog window is clicked, both the QLineEdit widget in the dialog and main window should be cleared.

Problem: When I inherit the main window class from the dialog class the method, clearUserID(), used to clear the User ID field fails to be invoked.

When I do not inherit from the main window class the clearUserID method works and I am able to clear the dialog QLineEdit (UserIDWin_UserID_lnedt) but not the corresponding widget on the main window (UserID_lnedt). All of the code I've tried to clear the main window QLineEdit widget using the dialog "Clear" button caused my program to crash.

Would somebody please help me to better understand the logic behind these principles and how to get my code working? Thank you.

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(820, 611)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.tabWidget = QtWidgets.QTabWidget(self.centralwidget)
        self.tabWidget.setGeometry(QtCore.QRect(0, 0, 801, 551))
        self.tabWidget.setObjectName("tabWidget")
        self.MainTab = QtWidgets.QWidget()
        self.MainTab.setObjectName("MainTab")
        self.UserID_Edit_pb = QtWidgets.QPushButton(self.MainTab)
        self.UserID_Edit_pb.setGeometry(QtCore.QRect(210, 10, 31, 23))
        self.UserID_Edit_pb.setObjectName("UserID_Edit_pb")
        self.UserID_Edit_pb.clicked.connect(self.openUserIDWin)
        self.UserID_Clear_pb_2 = QtWidgets.QPushButton(self.MainTab)
        self.UserID_Clear_pb_2.setGeometry(QtCore.QRect(170, 9, 41, 23))
        self.UserID_Clear_pb_2.setObjectName("UserID_Clear_pb_2")
        self.UserID_le = QtWidgets.QLineEdit(self.MainTab)
        self.label = QtWidgets.QLabel(self.MainTab)
        self.label.setGeometry(QtCore.QRect(10, 10, 47, 13))
        self.UserID_le.setGeometry(QtCore.QRect(50, 10, 113, 20))
        self.UserID_le.setObjectName("UserID_le")
        self.tabWidget.addTab(self.MainTab, "")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 820, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        self.tabWidget.setCurrentIndex(0)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

        self.UserID_Clear_pb_2.clicked.connect(self.UserID_le.clear)


    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.UserID_Edit_pb.setText(_translate("MainWindow", "Edit"))
        self.UserID_Clear_pb_2.setText(_translate("MainWindow", "Clear"))
        self.label.setText(_translate("MainWindow", "User ID"))
        self.tabWidget.setTabText(self.tabWidget.indexOf(self.MainTab), _translate("MainWindow", "Tab"))

    def openUserIDWin(self):
        UserID_value = self.UserID_le.text()
        UserIDWin = QtWidgets.QDialog()
        ui = Ui_UserIDWin(UserID_value)
        ui.setupUi(UserIDWin)
        UserIDWin.exec_();



class Ui_UserIDWin(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, userID):
        print("The User ID is:" + userID)
        self.userID = userID

    def setupUi(self, UserIDWin):
        UserIDWin.setObjectName("UserIDWin")
        UserIDWin.resize(400, 124)
        self.UserIDWin_UserID_lnedt = QtWidgets.QLineEdit(UserIDWin)
        self.UserIDWin_UserID_lnedt.setText(self.userID)
        self.UserIDWin_UserID_lnedt.setGeometry(QtCore.QRect(20, 50, 113, 20))
        self.UserIDWin_UserID_lnedt.setObjectName("UserIDWin_UserID_lnedt")
        self.UserIDWin_UserID_lbl = QtWidgets.QLabel(UserIDWin)
        self.UserIDWin_UserID_lbl.setGeometry(QtCore.QRect(20, 30, 47, 13))
        self.UserIDWin_UserID_lbl.setObjectName("UserIDWin_UserID_lbl")
        self.UserIDWin_UserIDClear_pushb = QtWidgets.QPushButton(UserIDWin)
        self.UserIDWin_UserIDClear_pushb.setGeometry(QtCore.QRect(140, 50, 41, 23))
        self.UserIDWin_UserIDClear_pushb.setObjectName("UserIDWin_UserIDClear_pushb")
        self.UserIDWin_Cancel_pushb = QtWidgets.QPushButton(UserIDWin)
        self.UserIDWin_Cancel_pushb.setGeometry(QtCore.QRect(110, 80, 75, 23))
        self.UserIDWin_Cancel_pushb.setObjectName("UserIDWin_Cancel_pushb")
        self.UserIDWin_Next_pushb = QtWidgets.QPushButton(UserIDWin)
        self.UserIDWin_Next_pushb.setGeometry(QtCore.QRect(190, 80, 75, 23))
        self.UserIDWin_Next_pushb.setObjectName("UserIDWin_Next_pushb")

        self.retranslateUi(UserIDWin)
        QtCore.QMetaObject.connectSlotsByName(UserIDWin)

        #If I do not inherit from "QtWidgets.QMainWindow, Ui_MainWindow" the code below works and invokes clearUserId().  However, I then am having problems using SetText on the main window UserId_le text box and the program crashes.
        self.UserIDWin_UserIDClear_pushb.clicked.connect(self.clearUserID)

    def retranslateUi(self, UserIDWin):
        _translate = QtCore.QCoreApplication.translate
        UserIDWin.setWindowTitle(_translate("UserIDWin", "Dialog"))
        self.UserIDWin_UserID_lbl.setText(_translate("UserIDWin", "User ID"))
        self.UserIDWin_UserIDClear_pushb.setText(_translate("UserIDWin", "Clear"))
        self.UserIDWin_Cancel_pushb.setText(_translate("UserIDWin", "Cancel"))
        self.UserIDWin_Next_pushb.setText(_translate("UserIDWin", "Next"))

    def clearUserID(self):
        self.UserIDWin_UserID_lnedt.setText('')
        # The line below crashes my program if I am able to invoke this method.
        #self.Ui_MainWindow.UserID_le.setText('')

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

Answer 1

It seems that they have certain clear concepts about inheritance and good practices but others do not like the following:

• PyQt recommends not modifying the code generated by Qt Designer because you probably want to modify the GUI in the future and when using pyuic the initial code is overwritten. Another problem is that beginners do not understand that the class generated by Qt Designer is not a widget but an interface that serves to fill another widget, and consequently can not overwrite the methods of the widgets in addition to other problems.

• You only have to modify the object of a class from the object of another class if both have the same scope, in your case when wanting to clean the QLineEdit of the main window from the other window is a dangerous task, instead you should do that logic where both windows have the same scope and that is in the openUserIDWin method.

• QLineEdit already has the clear() method that allows to clean, it fulfills the same function as setText("") but the first method is more readable.

Considering the above, the solution is:

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(820, 611)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.tabWidget = QtWidgets.QTabWidget(self.centralwidget)
        self.tabWidget.setGeometry(QtCore.QRect(0, 0, 801, 551))
        self.tabWidget.setObjectName("tabWidget")
        self.MainTab = QtWidgets.QWidget()
        self.MainTab.setObjectName("MainTab")
        self.UserID_Edit_pb = QtWidgets.QPushButton(self.MainTab)
        self.UserID_Edit_pb.setGeometry(QtCore.QRect(210, 10, 31, 23))
        self.UserID_Edit_pb.setObjectName("UserID_Edit_pb")
        self.UserID_Clear_pb_2 = QtWidgets.QPushButton(self.MainTab)
        self.UserID_Clear_pb_2.setGeometry(QtCore.QRect(170, 9, 41, 23))
        self.UserID_Clear_pb_2.setObjectName("UserID_Clear_pb_2")
        self.UserID_le = QtWidgets.QLineEdit(self.MainTab)
        self.label = QtWidgets.QLabel(self.MainTab)
        self.label.setGeometry(QtCore.QRect(10, 10, 47, 13))
        self.UserID_le.setGeometry(QtCore.QRect(50, 10, 113, 20))
        self.UserID_le.setObjectName("UserID_le")
        self.tabWidget.addTab(self.MainTab, "")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 820, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        self.tabWidget.setCurrentIndex(0)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.UserID_Edit_pb.setText(_translate("MainWindow", "Edit"))
        self.UserID_Clear_pb_2.setText(_translate("MainWindow", "Clear"))
        self.label.setText(_translate("MainWindow", "User ID"))
        self.tabWidget.setTabText(self.tabWidget.indexOf(self.MainTab), _translate("MainWindow", "Tab"))


class Ui_UserIDWin(object):
    def setupUi(self, UserIDWin):
        UserIDWin.setObjectName("UserIDWin")
        UserIDWin.resize(400, 124)
        self.UserIDWin_UserID_lnedt = QtWidgets.QLineEdit(UserIDWin)
        self.UserIDWin_UserID_lnedt.setGeometry(QtCore.QRect(20, 50, 113, 20))
        self.UserIDWin_UserID_lnedt.setObjectName("UserIDWin_UserID_lnedt")
        self.UserIDWin_UserID_lbl = QtWidgets.QLabel(UserIDWin)
        self.UserIDWin_UserID_lbl.setGeometry(QtCore.QRect(20, 30, 47, 13))
        self.UserIDWin_UserID_lbl.setObjectName("UserIDWin_UserID_lbl")
        self.UserIDWin_UserIDClear_pushb = QtWidgets.QPushButton(UserIDWin)
        self.UserIDWin_UserIDClear_pushb.setGeometry(QtCore.QRect(140, 50, 41, 23))
        self.UserIDWin_UserIDClear_pushb.setObjectName("UserIDWin_UserIDClear_pushb")
        self.UserIDWin_Cancel_pushb = QtWidgets.QPushButton(UserIDWin)
        self.UserIDWin_Cancel_pushb.setGeometry(QtCore.QRect(110, 80, 75, 23))
        self.UserIDWin_Cancel_pushb.setObjectName("UserIDWin_Cancel_pushb")
        self.UserIDWin_Next_pushb = QtWidgets.QPushButton(UserIDWin)
        self.UserIDWin_Next_pushb.setGeometry(QtCore.QRect(190, 80, 75, 23))
        self.UserIDWin_Next_pushb.setObjectName("UserIDWin_Next_pushb")

        self.retranslateUi(UserIDWin)
        QtCore.QMetaObject.connectSlotsByName(UserIDWin)

    def retranslateUi(self, UserIDWin):
        _translate = QtCore.QCoreApplication.translate
        UserIDWin.setWindowTitle(_translate("UserIDWin", "Dialog"))
        self.UserIDWin_UserID_lbl.setText(_translate("UserIDWin", "User ID"))
        self.UserIDWin_UserIDClear_pushb.setText(_translate("UserIDWin", "Clear"))
        self.UserIDWin_Cancel_pushb.setText(_translate("UserIDWin", "Cancel"))
        self.UserIDWin_Next_pushb.setText(_translate("UserIDWin", "Next"))


class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.setupUi(self)
        self.UserID_Edit_pb.clicked.connect(self.openUserIDWin)
        self.UserID_Clear_pb_2.clicked.connect(self.UserID_le.clear)

    def openUserIDWin(self):
        UserID_value = self.UserID_le.text()
        w = UserIDWin(UserID_value)
        w.UserIDWin_UserIDClear_pushb.clicked.connect(self.UserID_le.clear)
        w.exec_()


class UserIDWin(QtWidgets.QDialog, Ui_UserIDWin):
    def __init__(self, userID, parent=None):
        super(UserIDWin, self).__init__(parent)
        self.setupUi(self)
        self.userID = userID
        self.UserIDWin_UserID_lnedt.setText(self.userID)
        self.UserIDWin_UserIDClear_pushb.clicked.connect(self.UserIDWin_UserID_lnedt.clear)


if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())

I recommend you read:

• http://pyqt.sourceforge.net/Docs/PyQt5/designer.html
• QtDesigner changes will be lost after redesign User Interface