A class to load and use file associated icons

using System;
using System.Runtime.InteropServices;
using System.IO;
using System.Drawing;

namespace System.Windows.Forms
{
	public class SystemIconsImageList : IDisposable
	{
		#region Win32 declarations
		private const uint SHGFI_ICON = 0x100;
		private const uint SHGFI_LARGEICON = 0x0;
		private const uint SHGFI_SMALLICON = 0x1;

		[StructLayout(LayoutKind.Sequential)]
		public struct SHFILEINFO
		{
			public IntPtr hIcon;
			public IntPtr iIcon;
			public uint dwAttributes;
			[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
			public string szDisplayName;
			[MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
			public string szTypeName;
		};

		[DllImport("shell32.dll")]
		public static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);
		#endregion

		#region Fields
		private ImageList _smallImageList = new ImageList();
		private ImageList _largeImageList = new ImageList();
		private bool _disposed = false;
		#endregion

		#region Properties
		/// <summary>
		/// Gets System.Windows.Forms.ImageList with small icons in. Assign this property to SmallImageList of ListView, TreeView etc.
		/// </summary>
		public ImageList SmallIconsImageList
		{
			get { return _smallImageList; }
		}

		/// <summary>
		/// Gets System.Windows.Forms.ImageList with large icons in. Assign this property to LargeImageList of ListView, TreeView etc.
		/// </summary>
		public ImageList LargeIconsImageList
		{
			get { return _largeImageList; }
		}

		/// <summary>
		/// Gets number of icons were loaded
		/// </summary>
		public int Count
		{
			get { return _smallImageList.Images.Count; }
		}
		#endregion

		#region Constructor/Destructor
		/// <summary>
		/// Default constructor
		/// </summary>
		public SystemIconsImageList()
			: base()
		{
			_smallImageList.ColorDepth = ColorDepth.Depth32Bit;
			_smallImageList.ImageSize = SystemInformation.SmallIconSize;

			_largeImageList.ColorDepth = ColorDepth.Depth32Bit;
			_largeImageList.ImageSize = SystemInformation.IconSize;
		}

		private void CleanUp(bool disposing)
		{
			if (!this._disposed)
			{
				if (disposing)
				{
					_smallImageList.Dispose();
					_largeImageList.Dispose();
				}
			}
			_disposed = true;
		}

		/// <summary>
		/// Performs resource cleaning
		/// </summary>
		public void Dispose()
		{
			CleanUp(true);
			GC.SuppressFinalize(this);
		}

		~SystemIconsImageList()
		{
			CleanUp(false);
		}
		#endregion

		#region Public Methods
		/// <summary>
		/// Returns index of an icon based on FileName. Note: File should exists!
		/// </summary>
		/// <param name="FileName">Name of an existing File or Directory</param>
		/// <returns>Index of an Icon</returns>
		public int GetIconIndex(string FileName)
		{
			SHFILEINFO shinfo = new SHFILEINFO();

			FileInfo info = new FileInfo(FileName);

			string ext = info.Extension;
			if (String.IsNullOrEmpty(ext))
			{
				if ((info.Attributes & FileAttributes.Directory) != 0)
					ext = "5EEB255733234c4dBECF9A128E896A1E"; // for directories
				else
					ext = "F9EB930C78D2477c80A51945D505E9C4"; // for files without extension
			}
			else
				if (ext.Equals(".exe", StringComparison.InvariantCultureIgnoreCase) ||
					ext.Equals(".lnk", StringComparison.InvariantCultureIgnoreCase))
					ext = info.Name;

			if (_smallImageList.Images.ContainsKey(ext))
			{
				return _smallImageList.Images.IndexOfKey(ext);
			}
			else
			{
				SHGetFileInfo(FileName, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), SHGFI_ICON | SHGFI_SMALLICON);
				Icon smallIcon;
				try
				{
					smallIcon = Icon.FromHandle(shinfo.hIcon);
				}
				catch (ArgumentException ex)
				{
					throw new ArgumentException(String.Format("File \"{0}\" doesn not exist!", FileName), ex);
				}
				_smallImageList.Images.Add(ext, smallIcon);

				SHGetFileInfo(FileName, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), SHGFI_ICON | SHGFI_LARGEICON);
				Icon largeIcon = Icon.FromHandle(shinfo.hIcon);
				_largeImageList.Images.Add(ext, largeIcon);

				return _smallImageList.Images.Count - 1;
			}
		}
		#endregion
	}
}