[Interest] Qt5: Obtain current layout size

[Stephen Chu]

I am working on a dynamically generated form. One thing I'd like to do 
is to reflow the layout into multi-column when the widgets fill the 
preset window height.

I need to find out what the current layout height is before I add the 
new widget. The problem is, layout geometry is always 0x0 before the 
window is shown. And if I show the window before adding the widgets, not 
only does the window flickers badly, it also doesn't auto-position 
correctly. What's worse, the geometry reported is still 0x0.

So how do I get the correct layout or parent widget size before showing 
the widget/window? Thanks.