根据文件扩展名获取系统图标

       /// <summary>
       /// 根据文件后缀名获取系统图标。
       /// </summary>
       /// <param name="extension"></param>
       /// <returns></returns>
        public static ImageSource GetIconByExtension(string extension)
        {
            Icon smallIcon = null;
            Icon bigIcon = null;
            string describle = "";
            GetExtsIconAndDescription(extension, out bigIcon, out smallIcon, out describle);
            if (bigIcon != null)
            {
                Bitmap bitmap = bigIcon.ToBitmap();
                IntPtr hBitmap = bitmap.GetHbitmap();
                ImageSource imageSource =
                     System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
                          hBitmap, IntPtr.Zero, Int32Rect.Empty,
                          BitmapSizeOptions.FromEmptyOptions());
                return imageSource;
            }
  /// <summary> 
        /// 通过扩展名得到图标和描述 
        /// </summary> 
        /// <param name="ext">扩展名</param> 
        /// <param name="LargeIcon">得到大图标</param> 
        /// <param name="smallIcon">得到小图标</param> 
        public static void GetExtsIconAndDescription(string ext, out Icon largeIcon, out Icon smallIcon, out string description)
        {
            largeIcon = smallIcon = null;
            description = "";
            var extsubkey = Registry.ClassesRoot.OpenSubKey(ext); //从注册表中读取扩展名相应的子键 
            if (extsubkey != null)
            {
                var extdefaultvalue = (string)extsubkey.GetValue(null); //取出扩展名对应的文件类型名称 

                //未取到值，返回预设图标 
                if (extdefaultvalue == null)
                {
                    GetDefaultIcon(out largeIcon, out smallIcon);
                    return;
                }

                var typesubkey = Registry.ClassesRoot.OpenSubKey(extdefaultvalue); //从注册表中读取文件类型名称的相应子键 
                if (typesubkey != null)
                {
                    description = (string)typesubkey.GetValue(null); //得到类型描述字符串 
                    var defaulticonsubkey = typesubkey.OpenSubKey("DefaultIcon"); //取默认图标子键 
                    if (defaulticonsubkey != null)
                    {
                        //得到图标来源字符串 
                        var defaulticon = (string)defaulticonsubkey.GetValue(null); //取出默认图标来源字符串 
                        var iconstringArray = defaulticon.Split(',');
                        int nIconIndex = 0;
                        if (iconstringArray.Length > 1) int.TryParse(iconstringArray[1], out nIconIndex);
                        //得到图标 
                        System.IntPtr phiconLarge = new IntPtr();
                        System.IntPtr phiconSmall = new IntPtr();
                        ExtractIconExW(iconstringArray[0].Trim('"'), nIconIndex, ref phiconLarge, ref phiconSmall, 1);
                        if (phiconLarge.ToInt32() > 0) largeIcon = Icon.FromHandle(phiconLarge);
                        if (phiconSmall.ToInt32() > 0) smallIcon = Icon.FromHandle(phiconSmall);
                    }
                }
            }
        }
        /// <summary> 
        /// 获取缺省图标 
        /// </summary> 
        /// <param name="largeIcon"></param> 
        /// <param name="smallIcon"></param> 
        public static void GetDefaultIcon(out Icon largeIcon, out Icon smallIcon)
        {
            largeIcon = smallIcon = null;
            System.IntPtr phiconLarge = new IntPtr();
            System.IntPtr phiconSmall = new IntPtr();
            ExtractIconExW(Path.Combine(Environment.SystemDirectory, "shell32.dll"), 0, ref phiconLarge, ref phiconSmall, 1);
            if (phiconLarge.ToInt32() > 0) largeIcon = Icon.FromHandle(phiconLarge);
            if (phiconSmall.ToInt32() > 0) smallIcon = Icon.FromHandle(phiconSmall);
        }
        /// Return Type: UINT->unsigned int 
        ///lpszFile: LPCWSTR->WCHAR* 
        ///nIconIndex: int 
        ///phiconLarge: HICON* 
        ///phiconSmall: HICON* 
        ///nIcons: UINT->unsigned int 
        [DllImportAttribute("shell32.dll", EntryPoint = "ExtractIconExW", CallingConvention = System.Runtime.InteropServices.CallingConvention.StdCall)]
        public static extern uint ExtractIconExW([System.Runtime.InteropServices.InAttribute()] [System.Runtime.InteropServices.MarshalAsAttribute(UnmanagedType.LPWStr)] string lpszFile, int nIconIndex, ref IntPtr phiconLarge, ref IntPtr phiconSmall, uint nIcons);

        public static void CreateFileIcon(string fileType, out Icon large, out Icon small)
        {
            string des;

            if (fileType.Trim() == "") //预设图标
            {
                GetDefaultIcon(out large, out small);
            }
            else if (fileType.ToUpper() == ".EXE") //应用程序图标单独获取
            {
                IntPtr l = IntPtr.Zero;
                IntPtr s = IntPtr.Zero;

                ExtractIconExW(Path.Combine(Environment.SystemDirectory, "shell32.dll"), 2, ref l, ref s, 1);

                large = Icon.FromHandle(l);
                small = Icon.FromHandle(s);
            }
            else //其它类型的图标
            {
                GetExtsIconAndDescription(fileType, out large, out small, out des);
            }

            if ((large == null) || (small == null)) //无法获取图标,预设图标
                GetDefaultIcon(out large, out small);
        }
        public static byte[] ImageToByte(Image image)
        {
            MemoryStream ms = new MemoryStream();
            image.Save(ms, ImageFormat.Bmp);
            byte[] bs = ms.ToArray();
            ms.Close();
            return bs;
        }

        public static Image ByteToImage(byte[] bs)
        {
            MemoryStream ms = new MemoryStream(bs);
            Bitmap bmp = new Bitmap(ms);
            ms.Close();
            return bmp;
        }
        [StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
        public struct HICON__
        {
            public int unused;
        }
            return null;
        }