title: Qt Layout on QMainWindow
body: <p>I designed a <code>QMainWindow</code> with <code>QtCreator's</code> designer. It consists of the default central widget (a <code>QWidget</code>) which contains a <code>QVBoxLayout</code> with all the other widgets in it. Now everything I want, is that the <code>QVBoxLayout</code> automatically occupies the whole central widgets rectangle space.</p>
  
  <p>How can I do this? I didn't find any usable property neither in the central widgets properties nor the <code>QVBoxLayout's</code> ones.</p>