designer renders user control as empty content

I have a user control which renders its content at run time, based on the value of a property. So the XAML designer in Visual Studio is not able to show any content of the control when it is placed in a Window. Is there any way I can help the designer, tell it to set a specific property of the control to a value?

thanks,

Here is the user control. And the Window the control is placed in. When the XAML designer shows the window the control displays as empty.

<UserControl x:Class="wpfDemo.Controls.RadioButtonControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:local="clr-namespace:wpfDemo.Controls"
             mc:Ignorable="d"
             d:DesignHeight="300" d:DesignWidth="300"><Grid x:Name="grid1"></Grid></UserControl>


using System.Windows;
using System.Windows.Controls;

namespace wpfDemo.Controls
{
  /// <summary>
  /// Interaction logic for RadioButtonControl.xaml
  /// </summary>
  public partial class RadioButtonControl : UserControl
  {
    public int NumButton
    {
      get { return (int)GetValue(NumButtonProperty); }
      set { SetValue(NumButtonProperty, value); }
    }

    // Using a DependencyProperty as the backing store for NumButton.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty NumButtonProperty =
        DependencyProperty.Register("NumButton", typeof(int), typeof(RadioButtonControl),
          new PropertyMetadata(0, new PropertyChangedCallback(OnNumButtonChanged)));
    private static void OnNumButtonChanged(
      DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
      var numButton = e.NewValue as int?;
      var uc = d as RadioButtonControl;
      if ((uc != null) && (numButton != null))
      {
        uc.CreateButtons(numButton.Value);
      }
    }
    public RadioButtonControl()
    {
      InitializeComponent();
    }

    private void CreateButtons( int NumButton )
    {
      grid1.Children.Clear();

      var wrap1 = new WrapPanel();
      grid1.Children.Add(wrap1);

      for (int ix = 0; ix < NumButton; ++ix)
      {
        var rb = new RadioButton();
        rb.Content = "Button" + ix;
        rb.Name = "Button" + ix;
        wrap1.Children.Add(rb);
      }
    }
  }
}<Window x:Class="wpfDemo.steve5"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:wpfDemo"
        xmlns:uc="clr-namespace:wpfDemo.Controls"
        mc:Ignorable="d"
        Title="steve5" Height="300" Width="300"><StackPanel x:Name="layoutRoot" Orientation="Vertical"><uc:RadioButtonControl x:Name="control1" NumButton="{Binding NumButton}" /></StackPanel></Window>

using System.Windows;

namespace wpfDemo
{
  /// <summary>
  /// Interaction logic for steve5.xaml
  /// </summary>
  public partial class steve5 : Window
  {
    public steve5()
    {
      InitializeComponent();
      this.Loaded += Steve5_Loaded;
    }

    public int NumButton
    { get; set; }

    private void Steve5_Loaded(object sender, RoutedEventArgs e)
    {
      this.layoutRoot.DataContext = this;
      this.NumButton = 4;
    }
  }
}