C# does Shell, Part 4

using System;
using System.Runtime.InteropServices;

namespace ShellLib
{
	[ComImport]
	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
	[Guid("C0A651F5-B48B-11d2-B5ED-006097C686F6")]
	public interface IFolderFilterSite
	{
		// Exposed by a host to allow clients to pass the host their IUnknown interface pointers.
		[PreserveSig]
		Int32 SetFilter(
			[MarshalAs(UnmanagedType.Interface)]Object punk);		// A pointer to the client's IUnknown interface. To notify the host to terminate 
		// filtering and stop calling your IFolderFilter interface, set this parameter to NULL. 
	}
    
}