1.根据文件路径文件或文件夹图标获取 2.根据后缀获取系统图标

using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Drawing;

namespace CommonLibrary
{
    /// <summary>
    /// 根据文件名称获取文件的系统图标
    /// </summary>
    public static class IconUtilsByFilePath
    {
        [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;
        }

        ///<summary>  
        /// 返回系统设置的图标  
        ///</summary>  
        ///<param name="pszPath">文件路径 如果为""  返回文件夹的</param>  
        ///<param name="dwFileAttributes">0</param>  
        ///<param name="psfi">结构体</param>  
        ///<param name="cbSizeFileInfo">结构体大小</param>  
        ///<param name="uFlags">枚举类型</param>  
        ///<returns>-1失败</returns>  
        [DllImport("shell32.dll")]
        public static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref   SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);

        public enum SHGFI
        {
            SHGFI_ICON = 0x100,
            SHGFI_LARGEICON = 0x0,
            SHGFI_USEFILEATTRIBUTES = 0x10
        }


        ///<summary>  
        /// 获取文件图标 zgke@sina.com qq:116149  
        ///</summary>  
        ///<param name="p_Path">文件全路径</param>  
        ///<returns>图标</returns>  
        public static Icon GetFileIcon(string p_Path)
        {
            SHFILEINFO _SHFILEINFO = new SHFILEINFO();
            IntPtr _IconIntPtr = SHGetFileInfo(p_Path, 0, ref _SHFILEINFO, (uint)Marshal.SizeOf(_SHFILEINFO), (uint)(SHGFI.SHGFI_ICON | SHGFI.SHGFI_LARGEICON | SHGFI.SHGFI_USEFILEATTRIBUTES));
            if (_IconIntPtr.Equals(IntPtr.Zero)) return null;
            Icon _Icon = System.Drawing.Icon.FromHandle(_SHFILEINFO.hIcon);
            return _Icon;
        }
        ///<summary>  
        /// 获取文件夹图标  zgke@sina.com qq:116149  
        ///</summary>  
        ///<returns>图标</returns>  
        public static Icon GetDirectoryIcon()
        {
            SHFILEINFO _SHFILEINFO = new SHFILEINFO();
            IntPtr _IconIntPtr = SHGetFileInfo(@"", 0, ref _SHFILEINFO, (uint)Marshal.SizeOf(_SHFILEINFO), (uint)(SHGFI.SHGFI_ICON | SHGFI.SHGFI_LARGEICON));
            if (_IconIntPtr.Equals(IntPtr.Zero))
                return null;
            Icon _Icon = System.Drawing.Icon.FromHandle(_SHFILEINFO.hIcon);
            return _Icon;
        }
    }

    /// <summary>
    /// 根据文件的后缀获取文件的系统图标
    /// </summary>
    public static class IconUtilsByExtension
    {

        ///<summary>

        /// Used to access system folder icons.

        ///</summary>

        ///<param name="largeIcon">Specify large or small icons.</param>

        ///<param name="openFolder">Specify open or closed FolderType.</param>

        ///<returns>The requested Icon.</returns>

        public static Icon GetIconForFolder(Boolean largeIcon, Boolean openFolder)
        {

            SHFILEINFO shellFileInfo = new SHFILEINFO();

            try
            {

                uint flags = SHGFI_ICON | SHGFI_USEFILEATTRIBUTES;

                flags |= openFolder ? SHGFI_OPENICON : 0;

                flags |= largeIcon ? SHGFI_LARGEICON : SHGFI_SMALLICON;



                SHGetFileInfo(null,

                 FILE_ATTRIBUTE_DIRECTORY,

                 ref shellFileInfo,

                 (uint)Marshal.SizeOf(shellFileInfo),

                 flags);



                return (Icon)Icon.FromHandle(shellFileInfo.hIcon).Clone();

            }

            finally
            {

                DestroyIcon(shellFileInfo.hIcon);        // Cleanup

            }

        }



        ///<summary>

        /// Used to access file icons for a given extension.

        ///</summary>

        ///<param name="extension">The file extension to get the icon for.</param>

        ///<param name="largeIcon">Specify large or small icons.</param>

        ///<param name="linkOverlay">Specify link overlay on the icon.</param>


        ///<returns>The requested Icon</returns>

        public static Icon GetIconForFileExtension(String extension, Boolean largeIcon, Boolean linkOverlay)
        {

            if (!extension.StartsWith("."))

                extension = "." + extension;



            SHFILEINFO shellFileInfo = new SHFILEINFO();

            try
            {

                uint flags = SHGFI_ICON | SHGFI_USEFILEATTRIBUTES;

                flags |= linkOverlay ? SHGFI_LINKOVERLAY : 0;

                flags |= largeIcon ? SHGFI_LARGEICON : SHGFI_SMALLICON;



                SHGetFileInfo(extension,

                    FILE_ATTRIBUTE_NORMAL,

                    ref shellFileInfo,

                    (uint)Marshal.SizeOf(shellFileInfo),

                    flags);



                return (Icon)Icon.FromHandle(shellFileInfo.hIcon).Clone();

            }

            finally
            {

                DestroyIcon(shellFileInfo.hIcon);

            }

        }



        #region P/Invoke

        private const int MAX_PATH = 256;



        private const uint SHGFI_ICON = 0x000000100;

        private const uint SHGFI_LINKOVERLAY = 0x000008000;

        private const uint SHGFI_LARGEICON = 0x000000000;

        private const uint SHGFI_SMALLICON = 0x000000001;

        private const uint SHGFI_OPENICON = 0x000000002;

        private const uint SHGFI_USEFILEATTRIBUTES = 0x000000010;



        private const uint FILE_ATTRIBUTE_DIRECTORY = 0x00000010;

        private const uint FILE_ATTRIBUTE_NORMAL = 0x00000080;



        [StructLayout(LayoutKind.Sequential)]

        private struct SHFILEINFO
        {

            public const int NAMESIZE = 80;

            public IntPtr hIcon;

            public int iIcon;

            public uint dwAttributes;

            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = MAX_PATH)]

            public string szDisplayName;

            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = NAMESIZE)]

            public string szTypeName;

        };



        [DllImport("Shell32.dll")]

        private static extern IntPtr SHGetFileInfo(

            string pszPath,

            uint dwFileAttributes,

            ref SHFILEINFO psfi,

            uint cbFileInfo,

            uint uFlags

            );



        [DllImport("User32.dll")]

        private static extern int DestroyIcon(IntPtr hIcon);

        #endregion
    }
}