wxPython: ListBox not selectable/clickable when used with ComboCtrl

I am trying to couple wx.ListBox with wx.combo.Comboctrl. A sample code is below. For some reason, the items in the ListBox are not clickable/selectable. I wonder how I can make it work. Thanks!

import wx, wx.combo

class MainFrame(wx.Frame):
    def __init__(self, parent):
        wx.Frame.__init__(self, parent, title="", size=(300, 100))
        gbs = wx.GridBagSizer()
        ComboCtrlBox = wx.combo.ComboCtrl(self)
        ComboCtrlPopup = ListBoxComboPopup()
        ComboCtrlBox.SetPopupControl(ComboCtrlPopup)
        ComboCtrlPopup.ListBox.Append("Apple")
        ComboCtrlPopup.ListBox.Append("Banana")
        ComboCtrlPopup.ListBox.Append("Orange")

        gbs.Add(ComboCtrlBox, pos = (0, 0), span = (1, 1), flag = wx.EXPAND|wx.ALL, border = 10)
        gbs.AddGrowableCol(0)
        self.SetSizer(gbs)
        self.Layout()

class ListBoxComboPopup(wx.combo.ComboPopup):
    def Init(self):
        self.ItemList = []

    def Create(self, parent):
        self.ListBox = wx.ListBox(parent, -1, size = (-1, 20), choices = self.ItemList)

    def GetControl(self):
        retu self.ListBox

    def OnPopup(self):
        pass

#-----------------------------------------------------------------------------#

if __name__ == '__main__':
    APP = wx.App(False)
    FRAME = MainFrame(None)
    FRAME.Show()
    APP.MainLoop()