How to expand QDockWidget as main window grows

[martinb0820]

I'm using Qt 4.4.3 and Designer. I am trying to get a QDockWidget to resize automatically both horizontally and vertically (it does resize automatically vertically) as the user changes the main window size by dragging, as opposed to the user having to enlarge the dock widget via the splitter. A simplified example of the layout is attached.

I tried implementing resizeEvent() for the main window and resizing the dock widget to account for horizontal growth when it is called, but the dock widget's width seems to be "stuck". (I also tried this with setSizeConstraint(QLayout::SetNoConstraint).)

Are there other properties that need to be changed, or is another approach (e.g. a custom layout) necessary?

Thanks in advance,
Martin