Simple sizer question

[skol]

I have a SplitterWindow and two panels p1 and p2 in it.
I can put GenericDirCtrl into the left panel (p1),
however it (DirCtrl) stays small. I'd like to stretch it in the whole
of p1. The following code doesn't work, please help.

dir3 = wx.GenericDirCtrl(p1, -1, size=(-1,-1), style=... etc)
p1.sizer = wx.BoxSizer(wx.VERTICAL)
p1.sizer.Add(dir3, 1, wx.EXPAND)
p1.SetAutoLayout(True)
p1.SetSizer(p1.sizer)
p1.sizer.Fit(p1)