Code

void OnObjectBringToFront(object sender, RoutedEventArgs e)
{
	if (diagram.ActiveItem != null)
	{
		var cmd = new BringToFrontCmd(diagram.ActiveItem);
		diagram.ExecuteCommand(cmd);
	}
}

class BringToFrontCmd : Command
{
	public BringToFrontCmd(DiagramItem item) : base("Bring to front")
	{
		this.item = item;
		zIndex = item.ZIndex;
	}

	protected override void Execute(bool undoEnabled)
	{
		item.ZTop(true);
	}

	protected override void Undo()
	{
		item.ZIndex = zIndex;
	}

	protected override void Redo()
	{
		item.ZTop(true);
	}

	DiagramItem item;
	int zIndex;
}