WPF - creranje in postavitev kontrolnikov forma c code behiinde-u

Zanima me zakaj ne moremdodat kontrolnik v nek form, namenjen nastavitvam na naslednji način :

  private void SetOpacity_Click(object sender, RoutedEventArgs e)
        {
            
            Window win = new Window();
            win.Owner = this;
            win.ShowDialog();
            Slider slid = new Slider();
            
            slid.Parent = win;
            

            

        }