C#中读取“已注册的文件类型”的图标及读取指定文件图标的方法

程序代码
using System;
using System.IO;
using System.Drawing;
using Microsoft.Win32;
using System.Runtime.InteropServices;

namespace GetIconDemo
{
/// <summary>
/// 提供从操作系统读取图标的方法
/// </summary>
public class GetSystemIcon
{
/// <summary>
/// 依据文件名读取图标，若指定文件不存在，则返回空值。
/// </summary>
/// <param name="fileName"></param>
/// <returns></returns>
public static Icon GetIconByFileName(string fileName)
{
if (fileName == null || fileName.Equals(string.Empty)) return null;
if (!File.Exists(fileName)) return null;

SHFILEINFO shinfo = new SHFILEINFO();
//Use this to get the small Icon
Win32.SHGetFileInfo(fileName, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo), Win32.SHGFI_ICON | Win32.SHGFI_SMALLICON);
//The icon is returned in the hIcon member of the shinfo struct
System.Drawing.Icon myIcon = System.Drawing.Icon.FromHandle(shinfo.hIcon);
return myIcon;
}

/// <summary>
/// 给出文件扩展名（.*），返回相应图标
/// 若不以"."开头则返回文件夹的图标。
/// </summary>
/// <param name="fileType"></param>
/// <param name="isLarge"></param>
/// <returns></returns>
public static Icon GetIconByFileType(string fileType, bool isLarge)
{
if (fileType == null || fileType.Equals(string.Empty)) return null;

RegistryKey regVersion = null;
string regFileType = null;
string regIconString = null;
string systemDirectory = Environment.SystemDirectory + "//";

if (fileType[0] == '.')
{
//读系统注册表中文件类型信息
regVersion = Registry.ClassesRoot.OpenSubKey(fileType, true);
if (regVersion != null)
{
regFileType = regVersion.GetValue("") as string;
regVersion.Close();
regVersion = Registry.ClassesRoot.OpenSubKey(regFileType + @"/DefaultIcon", true);
if (regVersion != null)
{
regIconString = regVersion.GetValue("") as string;
regVersion.Close();
}
}
if (regIconString == null)
{
//没有读取到文件类型注册信息，指定为未知文件类型的图标
regIconString = systemDirectory + "shell32.dll,0";
}
}
else
{
//直接指定为文件夹图标
regIconString = systemDirectory + "shell32.dll,3";
}
string[] fileIcon = regIconString.Split(new char[] { ',' });
if (fileIcon.Length != 2)
{
//系统注册表中注册的标图不能直接提取，则返回可执行文件的通用图标
fileIcon = new string[] { systemDirectory + "shell32.dll", "2" };
}
Icon resultIcon = null;
try
{
//调用API方法读取图标
int[] phiconLarge = new int[1];
int[] phiconSmall = new int[1];
uint count = Win32.ExtractIconEx(fileIcon[0], Int32.Parse(fileIcon[1]), phiconLarge, phiconSmall, 1);
IntPtr IconHnd = new IntPtr(isLarge ? phiconLarge[0] : phiconSmall[0]);
resultIcon = Icon.FromHandle(IconHnd);
}
catch { }
return resultIcon;
}
}

[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>
/// 定义调用的API方法
/// </summary>
class Win32
{
public const uint SHGFI_ICON = 0x100;
public const uint SHGFI_LARGEICON = 0x0; // 'Large icon
public const uint SHGFI_SMALLICON = 0x1; // 'Small icon

[DllImport("shell32.dll")]
public static extern IntPtr SHGetFileInfo(string pszPath, uint dwFileAttributes, ref SHFILEINFO psfi, uint cbSizeFileInfo, uint uFlags);
[DllImport("shell32.dll")]
public static extern uint ExtractIconEx(string lpszFile, int nIconIndex, int[] phiconLarge, int[] phiconSmall, uint nIcons);

}
}