title: Callback when dependency property recieves xaml change
body: <p>When I set the value of <code>IsClosed</code> during runtime, <code>OnIsClosedChanged()</code> is called fine. 
  However, the Designer sets the value of the property but does not call the <code>OnIsClosedChanged()</code>. <br></p>
  
  <pre><code>public static DependencyProperty IsClosedProperty = DependencyProperty.Register("IsClosed", typeof(bool), typeof(GroupBox), new FrameworkPropertyMetadata(false, FrameworkPropertyMetadataOptions.AffectsRender));
  
  public bool IsClosed {
      get {
          return (bool)this.GetValue(IsClosedProperty);
      }
      set {
          if ((bool)this.GetValue(IsClosedProperty) == value)
              return;
  
          this.SetValue(IsClosedProperty, value);
          OnIsClosedChanged();
      }
  }
  
  
  
  private void OnIsClosedChanged() {
      _rowDefContent.Height = new GridLength((IsClosed ? 0 : 1), GridUnitType.Star);
  }
  </code></pre>
  
  <p>Obviously <code>IsClosed</code> is not modified by the Designer and only <code>IsClosedProperty</code> receives the xaml change. <br>
  My question is: How can I run <code>IsClosed</code> after the value has been modified in the Designer. Or at least add some logic to the non-runtime changes. </p>