Qcombobox in PyQt, How could I set the options in one combo box which depends on the choice of other combo box?

Question

For example, the first combo box with option A and option B. The second combo box contains option 1,2,3,4,5 if I select option A in 1st combo box. The second combo box contains option a,b,c,d,e if I select option B in 1st combo box.

How could I do this in PyQt5? I have searched Qcombobox class, there is 2 class activated and currentIndexChanged, but do not know which one I need to use and how to use it in PyQt5.

Answer 1

This is how I would do it:

import sys
from PyQt5 import QtWidgets


class ComboWidget(QtWidgets.QWidget):

    def __init__(self, parent=None):
        super(ComboWidget, self).__init__(parent)
        self.setGeometry(50, 50, 200, 200)

        layout = QtWidgets.QVBoxLayout(self)

        self.comboA = QtWidgets.QComboBox()
        # The second addItem parameter is itemData, which we will retrieve later
        self.comboA.addItem('A', ['1', '2', '3', '4'])
        self.comboA.addItem('B', ['a', 'b', 'c', 'd', 'e'])
        self.comboA.currentIndexChanged.connect(self.indexChanged)
        layout.addWidget(self.comboA)

        self.comboB = QtWidgets.QComboBox()
        # We could have added the 1,2,3,4 items directly, but the following
        # is a bit more generic in case the combobox starts with a different
        # index for some reason:
        self.indexChanged(self.comboA.currentIndex())
        layout.addWidget(self.comboB)

        self.show()

    def indexChanged(self, index):
        self.comboB.clear()
        data = self.comboA.itemData(index)
        if data is not None:
            self.comboB.addItems(data)


def main():
    app = QtWidgets.QApplication(sys.argv)
    w = ComboWidget()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

That way, your code is a bit more future-proof, as it would allow you to add / modify / remove the items in any of the dropdowns quite easily if you wanted to do so at some point.