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Posted 13 Mar 2003

C# does Shell, Part 4

, 26 Mar 2003
This article is about the AutoComplete features enabled by windows and how to use them with C#. AutoComplete is the ability to expand strings written in an edit box. The article will develop a class for using this functionality in you applications.
using System;
using System.Runtime.InteropServices;

namespace ShellLib
	public class FilterByExtension : 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.
		public Int32 ShouldShow(
			Object psf,				// A pointer to the folder's IShellFolder interface.
			IntPtr pidlFolder,		// The folder's PIDL.
			IntPtr pidlItem)		// The item's PIDL.
			// check extension, and if not ok return 1 (S_FALSE)
			// get display name of item
			ShellLib.IShellFolder isf = (ShellLib.IShellFolder)psf;

			ShellLib.ShellApi.STRRET ptrDisplayName;
			isf.GetDisplayNameOf(pidlItem,(uint)ShellLib.ShellApi.SHGNO.SHGDN_NORMAL | (uint)ShellLib.ShellApi.SHGNO.SHGDN_FORPARSING,out ptrDisplayName);
			String sDisplay;
			ShellLib.ShellApi.StrRetToBSTR(ref ptrDisplayName,(IntPtr)0,out sDisplay);
			// check if item is file or folder
			IntPtr[] aPidl = new IntPtr[1];
			aPidl[0] = pidlItem;
			uint Attrib;
			Attrib = (uint)ShellLib.ShellApi.SFGAO.SFGAO_FOLDER;

			int temp;
			temp = isf.GetAttributesOf(1,aPidl,ref Attrib);

			// if item is a folder, accept
			if ((Attrib & (uint)ShellLib.ShellApi.SFGAO.SFGAO_FOLDER) == (uint)ShellLib.ShellApi.SFGAO.SFGAO_FOLDER)
				return 0;

			// if item is file, check if it has a valid extension
			for (int i=0 ; i<ValidExtension.Length ; i++)
				if (sDisplay.ToUpper().EndsWith("." + ValidExtension[i].ToUpper()))
					return 0;

			return 1;

		// Allows a client to specify which classes of objects in a Shell folder should be enumerated.
		public Int32 GetEnumFlags( 
			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.
			return 0;

		public string[] ValidExtension;


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About the Author

Arik Poznanski
Software Developer (Senior) Verint
Israel Israel
Arik Poznanski is a senior software developer at Verint. He completed two B.Sc. degrees in Mathematics & Computer Science, summa cum laude, from the Technion in Israel.

Arik has extensive knowledge and experience in many Microsoft technologies, including .NET with C#, WPF, Silverlight, WinForms, Interop, COM/ATL programming, C++ Win32 programming and reverse engineering (assembly, IL).

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