title: XAML designed fails to load as cannot create a custom object
body: <p>I have a XAML form for use in my application, and I have subclassed the Frame class to create my own, and edited the interface to specify my own class for the content (as I need to access properties on the content for data binding).</p>
  
  <p>The problem comes then in the designer that the compiler says it cannot create an instance  of my control - I've tried to do some designer checks on the offending property bit but that didnt work either.</p>
  
  <p>How can I get the control to display? Works fine at runtime...</p>
  
  <p>XAML:</p>
  
  <pre><code>&lt;Grid Grid.Row="1" Grid.Column="1" Grid.ColumnSpan="2"&gt;
   &lt;views:PageFrame Name="Content_MainPage" Frame.NavigationUIVisibility="Hidden"/&gt;                    
  &lt;/Grid&gt;
  </code></pre>
  
  <p>CS:</p>
  
  <pre><code>        public new BaseView Content 
      {
          get
          {
              if (DesignerProperties.GetIsInDesignMode(this))
              {
                  return new BaseView();
              }
              else
              {
                  return (BaseView)base.Content;
              }
          }
          set
          {
              if (DesignerProperties.GetIsInDesignMode(this))
              {
                  base.Content = new BaseView();
                  FrameTitle = "design mode";
              }
              else
              {
                  base.Content = value;
                  FrameTitle = value.Title;
              }
          }
      }
  </code></pre>