QComboBox click event

Question

I have been trying to get a QComboBox in PyQt5 to become populated from a database table. The problem is trying to find a method that recognizes a click event on it.

In my GUI, my combo-box is initially empty, but upon clicking on it I wish for the click event to activate my method for communicating to the database and populating the drop-down list. It seems so far that there is no built-in event handler for a click-event for the combo-box. I am hoping that I am wrong on this. I hope someone will be able to tell me that there is a way to do this.

The best article I could find on my use-case here is from this link referring to PyQt4 QComboBox:

• dropdown event/callback in combo-box in pyqt4

I also found another link that contains a nice image of a QComboBox. The first element seems to be a label followed by a list:

• Catch mouse button pressed signal from QComboBox popup menu

Answer 1

You can override the showPopup method to achieve this, which will work no matter how the drop-down list is opened (i.e. via the mouse, keyboard, or shortcuts):

from PyQt5 import QtCore, QtWidgets

class ComboBox(QtWidgets.QComboBox):
    popupAboutToBeShown = QtCore.pyqtSignal()

    def showPopup(self):
        self.popupAboutToBeShown.emit()
        super(ComboBox, self).showPopup()

class Window(QtWidgets.QWidget):
    def __init__(self):
        super(Window, self).__init__()
        self.combo = ComboBox(self)
        self.combo.popupAboutToBeShown.connect(self.populateConbo)
        layout = QtWidgets.QVBoxLayout(self)
        layout.addWidget(self.combo)

    def populateConbo(self):
        if not self.combo.count():
            self.combo.addItems('One Two Three Four'.split())

if __name__ == '__main__':

    import sys
    app = QtWidgets.QApplication(sys.argv)
    window = Window()
    window.show()
    sys.exit(app.exec_())

However, for your particular use-case, I think a better solution might be to set a QSqlQueryModel on the combo-box, so that the items are updated from the database automatically.