Getting the associated icon for a file in C#

Sometimes it’s useful to display an icon for a file in an application and probably the best icon to display is whatever the operating system uses. The Windows API provides the SHGetFileInfo function for this purpose, so here’s a little wrapper around it. All the methods take a file name parameter, but the file doesn’t need to actually exist.

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace TestIcons
{
  public static class ImageUtilities
  {
    [StructLayout(LayoutKind.Sequential)]
    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;
    };

    static class Win32
    {
      internal const uint SHGFI_ICON = 0x100;
      internal const uint SHGFI_LARGEICON = 0x0; // 'Large icon
      internal const uint SHGFI_SMALLICON = 0x1; // 'Small icon
      internal const uint SHGFI_USEFILEATTRIBUTES = 0x10;
      internal const uint SHGFI_LINKOVERLAY = 0x8000;

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

      [DllImport("User32.dll")]
      public static extern int DestroyIcon(IntPtr hIcon);
    }

    public static Icon GetSmallIcon(string fileName)
    {
      return GetIcon(fileName, Win32.SHGFI_SMALLICON);
    }

    public static Icon GetSmallOverlayIcon(string fileName)
    {
      return GetIcon(fileName, Win32.SHGFI_SMALLICON | Win32.SHGFI_LINKOVERLAY);
    }

    public static Icon GetLargeIcon(string fileName)
    {
      return GetIcon(fileName, Win32.SHGFI_LARGEICON);
    }

    private static Icon GetIcon(string fileName, uint flags)
    {
      SHFILEINFO shinfo = new SHFILEINFO();
      IntPtr hImgSmall = Win32.SHGetFileInfo(fileName, 0, ref shinfo, (uint)Marshal.SizeOf(shinfo),
        Win32.SHGFI_ICON | Win32.SHGFI_USEFILEATTRIBUTES | flags);

      if (hImgSmall == IntPtr.Zero)
        return null;

      Icon icon = (Icon)Icon.FromHandle(shinfo.hIcon).Clone();
      Win32.DestroyIcon(shinfo.hIcon);
      return icon;
    }
  }
}