Sorry. I must be rather dense but I cannot see where in the link you provide there is a clue as to how answer the following question:-
Given:
DropList dl;
dl.Add(0, AttrText("This is bold")SetFont(Courier(25)).Bold());
Font font = ???
// Please replace the ??? with the appropriate code to obtain the Font object that is set in dl[0] above (which would be the appropriate Font object to pass to GetTextSize(..., font) for dl[0]).