[WxPython] Why is choicebox not displayed?

[merlem]

The code:

import wx

showliste = ["item1", "item2", "item3"]

class Mainframe(wx.Frame):
    def __init__(self, parent, id, title):
        wx.Frame.__init__(self, parent, id, title)
        
        self.shopanel = Shopanel(self, id)
        
        vbox = wx.BoxSizer(wx.VERTICAL) 
        vbox.Add(self.shopanel, 0, wx.EXPAND)
        
        self.SetSizer(vbox)

        self.Show()


class Shopanel(wx.Panel):
    def __init__(self, parent, id):
        wx.Panel.__init__(self, parent, id)
        
        self.SetMinSize((100, 100))
        self.SetMaxSize((150, 150))
        
        chos = wx.MultiChoiceDialog(self, "show:", "",
                                     showliste)
        chos.SetSelections(range(len(showliste[:-1])))
        
        hbox = wx.BoxSizer(wx.HORIZONTAL)
        hbox.Add(chos)
        self.SetSizerAndFit(hbox)
        


if __name__ == "__main__": 

    app = wx.App(0)
    Mainframe(None, -1, "Mainframe")  

    app.MainLoop() 

And two questions:
First and more important, why is the choicebox not shown? I simply get an empty window.
Second, how to make SetMinSize and SetMaxSize doing something, in the best case even influencing the panelsize? Actually, they just seem to do... nothing.