C# does Shell, Part 4

using System;
using System.Runtime.InteropServices;

namespace ShellLib
{
	[ComImport]
	[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
	[Guid("9CC22886-DC8E-11d2-B1D0-00C04F8EEB3E")]
	public interface IFolderFilter
	{
		// Allows a client to specify which individual items should be enumerated.
		// Note: The host calls this method for each item in the folder. Return S_OK, to have the item enumerated. 
		// Return S_FALSE to prevent the item from being enumerated.
		[PreserveSig] 
		Int32 ShouldShow(
			[MarshalAs(UnmanagedType.Interface)]Object psf,				// A pointer to the folder's IShellFolder interface.
			IntPtr pidlFolder,		// The folder's PIDL.
			IntPtr pidlItem);		// The item's PIDL.

		// Allows a client to specify which classes of objects in a Shell folder should be enumerated.
		[PreserveSig] 
		Int32 GetEnumFlags( 
			[MarshalAs(UnmanagedType.Interface)]Object psf,				// A pointer to the folder's IShellFolder interface.
			IntPtr pidlFolder,		// The folder's PIDL.
			IntPtr phwnd,			// A pointer to the host's window handle.
			out UInt32 pgrfFlags);	// One or more SHCONTF values that specify which classes of objects to enumerate.
		
	};

}