有很多软件如"WinRar" 能在它的文件列表中显示各类文件相关的图标。
在网上查了一下，发现可以用 SHGetFileInfo、ExtractAssociatedIcon等winapi函数根据文件获取文件在系统中对应的图标。
刚开始用的时候觉得好像它们只能返回存在的文件的图标。 若要用这些函数去根据扩展名获取图标，则需要先创建一个假文件, 获取图标后又删除，太麻烦。
后来重新查了一下，发现用SHGetFileInfo函数可以根据扩展名获取文件图标。
以下为示例代码。
using System;using System.Drawing;using System.Collections;using System.ComponentModel;using System.Data;using System.Runtime.InteropServices;namespace IconHelper
{
/// <summary>
/// Provides static methods to read system icons for both folders and files. /// </summary> /// <example> /// <code>IconReader.GetFileIcon("c:\\general.xls");</code>
/// </example> public class IconReader { /// <summary> /// Options to specify the size of icons to return. /// </summary> public enum IconSize { /// <summary> /// Specify large icon - 32 pixels by 32 pixels. /// </summary> Large = 0, /// <summary> /// Specify small icon - 16 pixels by 16 pixels. /// </summary> Small = 1 } /// <summary> /// Options to specify whether folders should be in the open or closed state. /// </summary> public enum FolderType { /// <summary> /// Specify open folder. /// </summary> Open = 0, /// <summary> /// Specify closed folder. /// </summary> Closed = 1 } /// <summary> /// Returns an icon for a given file - indicated by the name parameter. /// </summary> /// <param name="name">Pathname for file.</param> /// <param name="size">Large or small</param> /// <param name="linkOverlay">Whether to include the link icon</param> /// <returns>System.Drawing.Icon</returns> public static System.Drawing.Icon GetFileIcon(string name, IconSize size, bool linkOverlay) { Shell32.SHFILEINFO shfi = new Shell32.SHFILEINFO(); uint flags = Shell32.SHGFI_ICON | Shell32.SHGFI_USEFILEATTRIBUTES; if (true == linkOverlay) flags += Shell32.SHGFI_LINKOVERLAY; /* Check the size specified for return. */ if (IconSize.Small == size) { flags += Shell32.SHGFI_SMALLICON; } else { flags += Shell32.SHGFI_LARGEICON; } Shell32.SHGetFileInfo(name, Shell32.FILE_ATTRIBUTE_NORMAL, ref shfi, (uint)System.Runtime.InteropServices.Marshal.SizeOf(shfi), flags); // Copy (clone) the returned icon to a new object, thus allowing us to clean-up properly System.Drawing.Icon icon = (System.Drawing.Icon)System.Drawing.Icon.FromHandle(shfi.hIcon).Clone(); User32.DestroyIcon(shfi.hIcon); // Cleanup return icon; } /// <summary> /// Used to access system folder icons. /// </summary> /// <param name="size">Specify large or small icons.</param> /// <param name="folderType">Specify open or closed FolderType.</param> /// <returns>System.Drawing.Icon</returns> public static System.Drawing.Icon GetFolderIcon(IconSize size, FolderType folderType) { // Need to add size check, although errors generated at present! uint flags = Shell32.SHGFI_ICON | Shell32.SHGFI_USEFILEATTRIBUTES; if (FolderType.Open == folderType) { flags += Shell32.SHGFI_OPENICON; } if (IconSize.Small == size) { flags += Shell32.SHGFI_SMALLICON; } else { flags += Shell32.SHGFI_LARGEICON; } // Get the folder icon Shell32.SHFILEINFO shfi = new Shell32.SHFILEINFO(); Shell32.SHGetFileInfo(null, Shell32.FILE_ATTRIBUTE_DIRECTORY, ref shfi, (uint)System.Runtime.InteropServices.Marshal.SizeOf(shfi), flags); System.Drawing.Icon.FromHandle(shfi.hIcon); // Load the icon from an HICON handle // Now clone the icon, so that it can be successfully stored in an ImageList System.Drawing.Icon icon = (System.Drawing.Icon)System.Drawing.Icon.FromHandle(shfi.hIcon).Clone(); User32.DestroyIcon(shfi.hIcon); // Cleanup return icon; } } /// <summary> /// Wraps necessary Shell32.dll structures and functions required to retrieve Icon Handles using SHGetFileInfo. Code /// courtesy of MSDN Cold Rooster Consulting case study. /// </summary> /// // This code has been left largely untouched from that in the CRC example. The main changes have been moving // the icon reading code over to the IconReader type. public class Shell32 { public const int MAX_PATH = 256; [StructLayout(LayoutKind.Sequential)] public struct SHITEMID { public ushort cb; [MarshalAs(UnmanagedType.LPArray)] public byte[] abID; } [StructLayout(LayoutKind.Sequential)] public struct ITEMIDLIST { public SHITEMID mkid; } [StructLayout(LayoutKind.Sequential)] public struct BROWSEINFO { public IntPtr hwndOwner; public IntPtr pidlRoot; public IntPtr pszDisplayName; [MarshalAs(UnmanagedType.LPTStr)] public string lpszTitle; public uint ulFlags; public IntPtr lpfn; public int lParam; public IntPtr iImage; } // Browsing for directory. public const uint BIF_RETURNONLYFSDIRS = 0x0001; public const uint BIF_DONTGOBELOWDOMAIN = 0x0002; public const uint BIF_STATUSTEXT = 0x0004; public const uint BIF_RETURNFSANCESTORS = 0x0008; public const uint BIF_EDITBOX = 0x0010; public const uint BIF_VALIDATE = 0x0020; public const uint BIF_NEWDIALOGSTYLE = 0x0040; public const uint BIF_USENEWUI = (BIF_NEWDIALOGSTYLE | BIF_EDITBOX); public const uint BIF_BROWSEINCLUDEURLS = 0x0080; public const uint BIF_BROWSEFORCOMPUTER = 0x1000; public const uint BIF_BROWSEFORPRINTER = 0x2000; public const uint BIF_BROWSEINCLUDEFILES = 0x4000; public const uint BIF_SHAREABLE = 0x8000; [StructLayout(LayoutKind.Sequential)] public 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; }; public const uint SHGFI_ICON = 0x000000100; // get icon public const uint SHGFI_DISPLAYNAME = 0x000000200; // get display name public const uint SHGFI_TYPENAME = 0x000000400; // get type name public const uint SHGFI_ATTRIBUTES = 0x000000800; // get attributes public const uint SHGFI_ICONLOCATION = 0x000001000; // get icon location public const uint SHGFI_EXETYPE = 0x000002000; // return exe type public const uint SHGFI_SYSICONINDEX = 0x000004000; // get system icon index public const uint SHGFI_LINKOVERLAY = 0x000008000; // put a link overlay on icon public const uint SHGFI_SELECTED = 0x000010000; // show icon in selected state public const uint SHGFI_ATTR_SPECIFIED = 0x000020000; // get only specified attributes public const uint SHGFI_LARGEICON = 0x000000000; // get large icon public const uint SHGFI_SMALLICON = 0x000000001; // get small icon public const uint SHGFI_OPENICON = 0x000000002; // get open icon public const uint SHGFI_SHELLICONSIZE = 0x000000004; // get shell size icon public const uint SHGFI_PIDL = 0x000000008; // pszPath is a pidl public const uint SHGFI_USEFILEATTRIBUTES = 0x000000010; // use passed dwFileAttribute public const uint SHGFI_ADDOVERLAYS = 0x000000020; // apply the appropriate overlays public const uint SHGFI_OVERLAYINDEX = 0x000000040; // Get the index of the overlay public const uint FILE_ATTRIBUTE_DIRECTORY = 0x00000010; public const uint FILE_ATTRIBUTE_NORMAL = 0x00000080; [DllImport("Shell32.dll")] public static extern IntPtr SHGetFileInfo( string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbFileInfo, uint uFlags ); } /// <summary> /// Wraps necessary functions imported from User32.dll. Code courtesy of MSDN Cold Rooster Consulting example. /// </summary> public class User32 { /// <summary> /// Provides access to function required to delete handle. This method is used internally /// and is not required to be called separately. /// </summary> /// <param name="hIcon">Pointer to icon handle.</param> /// <returns>N/A</returns> [DllImport("User32.dll")] public static extern int DestroyIcon(IntPtr hIcon); }
}