How to set initial size of a TreeViewer?

I'm using a TreeViewer within a jface WizardPage and the initial input into the tree causes the WizardPage to grow vertically so that it can show all of the tree's values. When expanding one of the tree's values, then the vertical scrollbar works as expected. I'd开发者_如何学Go like to be able to set the tree's size initially so that it is fixed and the scrollbar is already shown when the WizardPage is first drawn, but doing this isn't particularly obvious to me - the setSize method on the TreeViewer's Tree doesn't seem to do anything.

Any help would be appreciated!

Just for the records for this old question:

We solve this problem in our applications by using an own layout manager which we can set fixed sizes for certain controls (with Swing we had done that by using component.setPreferredSize(size)). If no such fixed size is used, we calculate the preferred size of the control while performing the layout. This prevents making controls getting more and more space depending on the control's content when the user resizes the application window or dialog.