WPF

using (FileStream stream = new FileStream("text.xaml", FileMode.Create, FileAccess.Write))
{
  XmlWriterSettings settings = new XmlWriterSettings();
                settings.Indent = true;
                settings.ConformanceLevel = ConformanceLevel.Auto;
                XmlWriter writer = XmlWriter.Create(stream, settings);
                XamlDesignerSerializationManager manager = new XamlDesignerSerializationManager(writer);
                manager.XamlWriterMode = XamlWriterMode.Expression;
                XamlWriter.Save(Viewport, manager);
            }

ModelVisual3D model = new ModelVisual3D();
model.Content = new GeometryModel3D(MeshPrimitives.Box(10, 10, 10), new DiffuseMaterial(new SolidColorBrush(Colors.Red)));
model.Transform = new TranslateTransform3D(new Vector3D(0, 20, 0));
model.SetValue(FrameworkElement.NameProperty, "SomeBox");

Viewport.Children.Add(model);

public class UDPTabItem : TabItem
{
    public bool           IsActive { get; set; }

    //--------------------------------------------------------------------------------
    //--------------------------------------------------------------------------------
    // Create a custom routed event by first registering a RoutedEventID.  This event
    // uses the bubbling routing strategy
    public static readonly RoutedEvent ActivateEvent = EventManager.RegisterRoutedEvent("Activate",
                                           RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(UDPTabItem));
    // Provide CLR accessors for the events
    public event RoutedEventHandler Activate
    {
        add    { AddHandler(ActivateEvent, value);    }
        remove { RemoveHandler(ActivateEvent, value); }
    }
    // These methods raise the events
    private void RaiseActivateEvent()
    {
        RoutedEventArgs eventArgs = new RoutedEventArgs(UDPTabItem.ActivateEvent);
        RaiseEvent(eventArgs);
    }


    //--------------------------------------------------------------------------------
    //--------------------------------------------------------------------------------
    public static readonly RoutedEvent DeactivateEvent = EventManager.RegisterRoutedEvent("Deactivate",
                              RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(UDPTabItem));
    public event RoutedEventHandler Deactivate
    {
        add    { AddHandler(DeactivateEvent, value);    }
        remove { RemoveHandler(DeactivateEvent, value); }
    }
    private void RaiseDeactivateEvent()
    {
        RoutedEventArgs eventArgs = new RoutedEventArgs(UDPTabItem.DeactivateEvent);
        RaiseEvent(eventArgs);
    }


    //--------------------------------------------------------------------------------
    /// <summary>
    ///
    /// </summary>
    public UDPTabItem()
    {
        this.IsActive = false;
    }

    //--------------------------------------------------------------------------------
    /// <summary>
    ///
    /// </summary>
    /// <param name="activate"></param>
    public void ActivateTab(bool activate)
    {
        IsActive = activate;
        if (this.IsActive)
        {
            RaiseActivateEvent();
        }
        else
        {
            RaiseDeactivateEvent();
        }
    }

    //--------------------------------------------------------------------------------
    /// <summary>
    ///
    /// </summary>
    /// <param name="e"></param>
    protected override void OnSelected(RoutedEventArgs e)
    {
        ActivateTab(true);
        base.OnSelected(e);
    }

    //--------------------------------------------------------------------------------
    /// <summary>
    ///
    /// </summary>
    /// <param name="e"></param>
    protected override void OnUnselected(RoutedEventArgs e)
    {
        ActivateTab(false);
        base.OnUnselected(e);
    }

}