ciao!

ho creato una finestra in qt con dentro un oggetto QMdiSubWindow.
la finestra la avvio massimizzata:
codice:
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    this->showMaximized();
}
e fin qui tutto ok.
a questo punto ho impostato la proprietà sizePolicy su Expanding sia al centralWidget, che al QMdiSubWindow.
però queste non si allungano e allargano, ma rimangono alla dimensione iniziale che ho impostato (mi pare di capire che una dimensione iniziale ce l'hanno sempre).
provo a postare anche il file ui:
codice:
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>900</width>
    <height>900</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Cimoda Admin</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <property name="sizePolicy">
    <sizepolicy hsizetype="Expanding" vsizetype="Expanding">
     <horstretch>1</horstretch>
     <verstretch>1</verstretch>
    </sizepolicy>
   </property>
   <widget class="QMdiArea" name="mdiArea">
    <property name="geometry">
     <rect>
      <x>0</x>
      <y>0</y>
      <width>901</width>
      <height>881</height>
     </rect>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>900</width>
     <height>20</height>
    </rect>
   </property>
   <widget class="QMenu" name="menuFile">
    <property name="title">
     <string>File</string>
    </property>
    <addaction name="actionClienti"/>
    <addaction name="actionAgenti"/>
    <addaction name="actionChiudi"/>
   </widget>
   <addaction name="menuFile"/>
  </widget>
  <action name="actionClienti">
   <property name="text">
    <string>Clienti</string>
   </property>
  </action>
  <action name="actionAgenti">
   <property name="text">
    <string>Agenti</string>
   </property>
  </action>
  <action name="actionChiudi">
   <property name="text">
    <string>Chiudi</string>
   </property>
   <property name="shortcut">
    <string>Ctrl+Q</string>
   </property>
  </action>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections>
  <connection>
   <sender>actionChiudi</sender>
   <signal>triggered()</signal>
   <receiver>MainWindow</receiver>
   <slot>close()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>-1</x>
     <y>-1</y>
    </hint>
    <hint type="destinationlabel">
     <x>449</x>
     <y>449</y>
    </hint>
   </hints>
  </connection>
 </connections>
</ui>
come faccio a fare in modo che il tutto si allarghialla stessa dimensione della finestra??