public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();

Canvas c = new Canvas();
AddChild(c);

Rectangle r = new Rectangle();
c.Children.Add(r);

FrameworkElement e = r.Parent as FrameworkElement;
while (e != null && !(e is Window))
{
e = e.Parent as FrameworkElement;
}
}
}