One of the quirk with QT 4.5 is that in order to get your entire application to resize (all the elements within it), they have to be within a layout. However, the QT Designer won’t let you assign a layout to empty QWidgets, especially if they are inside the tab widget. So this is how I go about solving the problem.

  1. Add a vertical layout into each of the QWidget inside the tab. (You need this for the whole application to resize, anyway)
  2. Click on the QWidget (not in the hierarchy!), right click and add a Layout. By this time, the “no entry” icon next to that widget would disappear
  3. If you are dynamically adding widgets to the tab during run-time, you have to add to the vertical layout inside the QWidget of that tab.

If I have more time, I would put up a step by step tutoiral.