[qt] Auto-expanding layout with Qt-Designer

According to the documentation, there needs to be a top level layout set.

A top level layout is necessary to ensure that your widgets will resize correctly when its window is resized. To check if you have set a top level layout, preview your widget and attempt to resize the window by dragging the size grip.

You can set one by clearing the selection and right clicking on the form itself and choosing one of the layouts available in the context menu.

Qt layouts