python - How to pass the value from class MainWindow to the class of the DockWidget

Question

I wrote this small Application using pyqt5: from the menubar of the MainWindow I can choose a folder and I would like to pass the path of the choosen folder to the QLineEdit "txtPath" which is in the other class named "YtDownloader". I stuck in this issue since "txtPath" is unknown from the MainWindow.

import sys
from PyQt5 import QtWidgets as qtw
from PyQt5 import QtGui as qtg
from PyQt5 import QtCore as qtc

class YtDownloader(qtw.QWidget):
    def __init__(self):
        super().__init__()
        self.setLayout(qtw.QFormLayout())
        self.txtPath = qtw.QLineEdit(placeholderText='Select the download path from the menu')

        self.layout().addRow(self.txtPath)

class MainWindow(qtw.QMainWindow):
    def __init__(self):
        super().__init__()
        # Main UI code goes here

        # Menubar
        menubar = self.menuBar()
        file_menu = menubar.addMenu('File')
        file_menu.addAction('Select Download Folder', self.getDownloadFolder)

        # Central Widget
        self.lstStream = qtw.QListWidget()
        self.setCentralWidget(self.lstStream)

        # Dockable Widget
        ytd_dock = qtw.QDockWidget('Dock Panel')
        self.addDockWidget(qtc.Qt.RightDockWidgetArea, ytd_dock)
        ytd_dock.setFeatures(qtw.QDockWidget.DockWidgetMovable | qtw.QDockWidget.DockWidgetFloatable)

        ytd_widget = YtDownloader()
        ytd_dock.setWidget(ytd_widget)

        # End main UI code
        self.show()

    def getDownloadFolder(self):
        try:
            self.dirname = qtw.QFileDialog.getExistingDirectory()
            if self.dirname:
                # self.txtPath.setText(self.dirname) --> this does not work
                qtw.QMessageBox.information(self, '', self.dirname)
        except Exception as e:
            qtw.QMessageBox.critical(self, 'Error', str(e))

if __name__ == '__main__':
    app = qtw.QApplication(sys.argv)
    # it's required to save a reference to MainWindow.
    # if it goes out of scope, it will be destroyed.
    mw = MainWindow()
    sys.exit(app.exec())

Answer 1

The problem is simple: which object does the txtPath attribute belong to? Well, to an object of the YtDownloader class but "self" is not an object of that type, that is why this exception is thrown. The solution is to make the "ytd_widget" attribute of the class so that it can be accessible, and then use that attribute to access the "txtPath".

class MainWindow(qtw.QMainWindow):
    def __init__(self):
        super().__init__()
        # Main UI code goes here

        # Menubar
        menubar = self.menuBar()
        file_menu = menubar.addMenu("File")
        file_menu.addAction("Select Download Folder", self.getDownloadFolder)

        # Central Widget
        self.lstStream = qtw.QListWidget()
        self.setCentralWidget(self.lstStream)

        # Dockable Widget
        ytd_dock = qtw.QDockWidget("Dock Panel")
        self.addDockWidget(qtc.Qt.RightDockWidgetArea, ytd_dock)
        ytd_dock.setFeatures(
            qtw.QDockWidget.DockWidgetMovable | qtw.QDockWidget.DockWidgetFloatable
        )

        self.ytd_widget = YtDownloader()
        ytd_dock.setWidget(self.ytd_widget)

        # End main UI code
        self.show()

    def getDownloadFolder(self):
        dirname = qtw.QFileDialog.getExistingDirectory()
        if dirname:
            self.ytd_widget.txtPath.setText(dirname)