Resize window when Expander is collapsed

[Tiberius Duluman <tiberius duluman gmail com>]

I have a dialog that contains several widgets to collect data from the user.
Last widget is an Expander that hides some advanced and not mandatory data.
When the dialog is opened, the Expander is collapsed. If the user 
expands the
Expander, the window is resized so all the controls fits into the dialog.
But, when the Expander is collapsed, the dialog is not resized back to a
smaller size, so all the widgets appear sparse.
I've tried to resize the dialog on the changed signal of expanded property,
but it did not work. I've also tried to connect an idle handle on the 
changed signal
and resize the window from the connected idle handler, but it did not 
work also.
Does anybody have any idea how I can resize the dialog when the expander 
is collapsed?