Currently there is no way to know when VerticalLayoutContainer will display its scrollbar. This causes a problem because when setting the size of content in the VerticalLayoutContainer one can't accurately know how big the viewable area will be.
What I do now is in my addResizeHandler() I get the best estimate of the VerticalLayoutContainer's client size by calling getElement().getClientWidth() & getElement().getClientHeight() and this works sometimes. It always works after a manual resize but when first sized those methods don't always account for the scrollbar size...but sometimes they do. So it seems indeterminate when those methods will 'know' about the scrollbar.
It seems an ideal solution would be to be able to register a scroll handler that has events of when the scrollbar is visible/hidden.
If there is another way I can 'defer' calling getElement().getClientWidth() & getElement().getClientHeight() until after the it's guaranteed they will know about the scrollbar please advise as that too may be a possible solution.