Set VirtualizingStackPanel properties for dynamically created StackPanel

Hi, for a dynamically created StackPanel how can I set the properties VirtualizingStackPanel.IsVirtualizing and VirtualizingStackPanel.VirtualizationMode ?

The code-behind intellisense doesn't show these properties on the StackPanel though available in xaml UI stackpanel control)

StackPanel sp = new StackPanel();

If I use VirtualizingStackPanel instead of StackPanel, then I don't see the children on expanding this control at runtime

VirtualizingStackPanel vsp = new VirtualizingStackPanel();

Thanks,

-srinivas y.

sri