How do I get common file type icons in C#?

Question

As seen in This SO question on getting icons for common file types, it's quite possible for a windows program to get the icons for a registered file type using the C++ Shell API. These icons may or may not exist on disk - for example, we wanted to make our own custom file browser and want to display the system-associated icon with the file.

Is there a native C# way to get the icons for various file types (and if so, how) or must it be done through PInvoke with shell API?

And as a follow up, if there is a native .NET way of doing it, is there a cross-platform way of doing it?

Answer 1

One of my old open source project include an Icon class that does exactly that, feel free to rip it, seeing the age I put this file in the public domain anyway it's just PInvoke for most part.

To get an icon you use for example :

Icon zipIcon = BlackFox.Win32.Icons.IconFromExtension(".zip", SystemIconSize.Small);

Full sample :

using System;
using System.Windows.Forms;
using BlackFox.Win32;
using System.Drawing;

class Program
{
    static void Main(string[] args)
    {
        PictureBox pict = new PictureBox();
        pict.Image = Icons.IconFromExtension(".zip", Icons.SystemIconSize.Large).ToBitmap();
        pict.Dock = DockStyle.Fill;
        pict.SizeMode = PictureBoxSizeMode.CenterImage;

        Form form = new Form();
        form.Controls.Add(pict);

        Application.Run(form);        
    }
}

The library :

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using Microsoft.Win32;
using System.Reflection;
using System.Collections.Generic;

namespace BlackFox.Win32
{
    public static class Icons
    {
        #region Custom exceptions class

        public class IconNotFoundException : Exception
        {
            public IconNotFoundException(string fileName, int index)
                : base(string.Format("Icon with Id = {0} wasn't found in file {1}", index, fileName))
            {
            }
        }

        public class UnableToExtractIconsException : Exception
        {
            public UnableToExtractIconsException(string fileName, int firstIconIndex, int iconCount)
                : base(string.Format("Tryed to extract {2} icons starting from the one with id {1} from the \"{0}\" file but failed", fileName, firstIconIndex, iconCount))
            {
            }
        }

        #endregion

        #region DllImports

        /// <summary>
        /// Contains information about a file object. 
        /// </summary>
        struct SHFILEINFO
        {
            /// <summary>
            /// Handle to the icon that represents the file. You are responsible for
            /// destroying this handle with DestroyIcon when you no longer need it. 
            /// </summary>
            public IntPtr hIcon;

            /// <summary>
            /// Index of the icon image within the system image list.
            /// </summary>
            public IntPtr iIcon;

            /// <summary>
            /// Array of values that indicates the attributes of the file object.
            /// For information about these values, see the IShellFolder::GetAttributesOf
            /// method.
            /// </summary>
            public uint dwAttributes;

            /// <summary>
            /// String that contains the name of the file as it appears in the Microsoft
            /// Windows Shell, or the path and file name of the file that contains the
            /// icon representing the file.
            /// </summary>
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public string szDisplayName;

            /// <summary>
            /// String that describes the type of file.
            /// </summary>
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]
            public string szTypeName;
        };

        [Flags]
        enum FileInfoFlags : int
        {
            /// <summary>
            /// Retrieve the handle to the icon that represents the file and the index 
            /// of the icon within the system image list. The handle is copied to the 
            /// hIcon member of the structure specified by psfi, and the index is copied 
            /// to the iIcon member.
            /// </summary>
            SHGFI_ICON = 0x000000100,
            /// <summary>
            /// Indicates that the function should not attempt to access the file 
            /// specified by pszPath. Rather, it should act as if the file specified by 
            /// pszPath exists with the file attributes passed in dwFileAttributes.
            /// </summary>
            SHGFI_USEFILEATTRIBUTES = 0x000000010
        }

        /// <summary>
        ///     Creates an array of handles to large or small icons extracted from
        ///     the specified executable file, dynamic-link library (DLL), or icon
        ///     file. 
        /// </summary>
        /// <param name="lpszFile">
        ///     Name of an executable file, DLL, or icon file from which icons will
        ///     be extracted.
        /// </param>
        /// <param name="nIconIndex">
        ///     <para>
        ///         Specifies the zero-based index of the first icon to extract. For
        ///         example, if this value is zero, the function extracts the first
        ///         icon in the specified file.
        ///     </para>
        ///     <para>
        ///         If this value is �1 and <paramref name="phiconLarge"/> and
        ///         <paramref name="phiconSmall"/> are both NULL, the function returns
        ///         the total number of icons in the specified file. If the file is an
        ///         executable file or DLL, the return value is the number of
        ///         RT_GROUP_ICON resources. If the file is an .ico file, the return
        ///         value is 1. 
        ///     </para>
        ///     <para>
        ///         Windows 95/98/Me, Windows NT 4.0 and later: If this value is a 
        ///         negative number and either <paramref name="phiconLarge"/> or 
        ///         <paramref name="phiconSmall"/> is not NULL, the function begins by
        ///         extracting the icon whose resource identifier is equal to the
        ///         absolute value of <paramref name="nIconIndex"/>. For example, use -3
        ///         to extract the icon whose resource identifier is 3. 
        ///     </para>
        /// </param>
        /// <param name="phIconLarge">
        ///     An array of icon handles that receives handles to the large icons
        ///     extracted from the file. If this parameter is NULL, no large icons
        ///     are extracted from the file.
        /// </param>
        /// <param name="phIconSmall">
        ///     An array of icon handles that receives handles to the small icons
        ///     extracted from the file. If this parameter is NULL, no small icons
        ///     are extracted from the file. 
        /// </param>
        /// <param name="nIcons">
        ///     Specifies the number of icons to extract from the file. 
        /// </param>
        /// <returns>
        ///     If the <paramref name="nIconIndex"/> parameter is -1, the
        ///     <paramref name="phIconLarge"/> parameter is NULL, and the
        ///     <paramref name="phiconSmall"/> parameter is NULL, then the return
        ///     value is the number of icons contained in the specified file.
        ///     Otherwise, the return value is the number of icons successfully
        ///     extracted from the file. 
        /// </returns>
        [DllImport("Shell32", CharSet = CharSet.Auto)]
        extern static int ExtractIconEx(
            [MarshalAs(UnmanagedType.LPTStr)] 
            string lpszFile,
            int nIconIndex,
            IntPtr[] phIconLarge,
            IntPtr[] phIconSmall,
            int nIcons);

        [DllImport("Shell32", CharSet = CharSet.Auto)]
        extern static IntPtr SHGetFileInfo(
            string pszPath,
            int dwFileAttributes,
            out SHFILEINFO psfi,
            int cbFileInfo,
            FileInfoFlags uFlags);

        #endregion

        /// <summary>
        /// Two constants extracted from the FileInfoFlags, the only that are
        /// meaningfull for the user of this class.
        /// </summary>
        public enum SystemIconSize : int
        {
            Large = 0x000000000,
            Small = 0x000000001
        }

        /// <summary>
        /// Get the number of icons in the specified file.
        /// </summary>
        /// <param name="fileName">Full path of the file to look for.</param>
        /// <returns></returns>
        static int GetIconsCountInFile(string fileName)
        {
            return ExtractIconEx(fileName, -1, null, null, 0);
        }

        #region ExtractIcon-like functions

        public static void ExtractEx(string fileName, List<Icon> largeIcons,
            List<Icon> smallIcons, int firstIconIndex, int iconCount)
        {
            /*
             * Memory allocations
             */

            IntPtr[] smallIconsPtrs = null;
            IntPtr[] largeIconsPtrs = null;

            if (smallIcons != null)
            {
                smallIconsPtrs = new IntPtr[iconCount];
            }
            if (largeIcons != null)
            {
                largeIconsPtrs = new IntPtr[iconCount];
            }

            /*
             * Call to native Win32 API
             */

            int apiResult = ExtractIconEx(fileName, firstIconIndex, largeIconsPtrs, smallIconsPtrs, iconCount);
            if (apiResult != iconCount)
            {
                throw new UnableToExtractIconsException(fileName, firstIconIndex, iconCount);
            }

            /*
             * Fill lists
             */

            if (smallIcons != null)
            {
                smallIcons.Clear();
                foreach (IntPtr actualIconPtr in smallIconsPtrs)
                {
                    smallIcons.Add(Icon.FromHandle(actualIconPtr));
                }
            }
            if (largeIcons != null)
            {
                largeIcons.Clear();
                foreach (IntPtr actualIconPtr in largeIconsPtrs)
                {
                    largeIcons.Add(Icon.FromHandle(actualIconPtr));
                }
            }
        }

        public static List<Icon> ExtractEx(string fileName, SystemIconSize size,
            int firstIconIndex, int iconCount)
        {
            List<Icon> iconList = new List<Icon>();

            switch (size)
            {
                case SystemIconSize.Large:
                    ExtractEx(fileName, iconList, null, firstIconIndex, iconCount);
                    break;

                case SystemIconSize.Small:
                    ExtractEx(fileName, null, iconList, firstIconIndex, iconCount);
                    break;

                default:
                    throw new ArgumentOutOfRangeException("size");
            }

            return iconList;
        }

        public static void Extract(string fileName, List<Icon> largeIcons, List<Icon> smallIcons)
        {
            int iconCount = GetIconsCountInFile(fileName);
            ExtractEx(fileName, largeIcons, smallIcons, 0, iconCount);
        }

        public static List<Icon> Extract(string fileName, SystemIconSize size)
        {
            int iconCount = GetIconsCountInFile(fileName);
            return ExtractEx(fileName, size, 0, iconCount);
        }

        public static Icon ExtractOne(string fileName, int index, SystemIconSize size)
        {
            try
            {
                List<Icon> iconList = ExtractEx(fileName, size, index, 1);
                return iconList[0];            
            }
            catch (UnableToExtractIconsException)
            {
                throw new IconNotFoundException(fileName, index);
            }
        }

        public static void ExtractOne(string fileName, int index,
            out Icon largeIcon, out Icon smallIcon)
        {
            List<Icon> smallIconList = new List<Icon>();
            List<Icon> largeIconList = new List<Icon>();
            try
            {
                ExtractEx(fileName, largeIconList, smallIconList, index, 1);
                largeIcon = largeIconList[0];
                smallIcon = smallIconList[0];
            }
            catch (UnableToExtractIconsException)
            {
                throw new IconNotFoundException(fileName, index);
            }
        }

        #endregion

        //this will look throw the registry 
        //to find if the Extension have an icon.
        public static Icon IconFromExtension(string extension,
                                                SystemIconSize size)
        {
            // Add the '.' to the extension if needed
            if (extension[0] != '.') extension = '.' + extension;

            //opens the registry for the wanted key.
            RegistryKey Root = Registry.ClassesRoot;
            RegistryKey ExtensionKey = Root.OpenSubKey(extension);
            ExtensionKey.GetValueNames();
            RegistryKey ApplicationKey =
                Root.OpenSubKey(ExtensionKey.GetValue("").ToString());

            //gets the name of the file that have the icon.
            string IconLocation =
                ApplicationKey.OpenSubKey("DefaultIcon").GetValue("").ToString();
            string[] IconPath = IconLocation.Split(',');

            if (IconPath[1] == null) IconPath[1] = "0";
            IntPtr[] Large = new IntPtr[1], Small = new IntPtr[1];

            //extracts the icon from the file.
            ExtractIconEx(IconPath[0],
                Convert.ToInt16(IconPath[1]), Large, Small, 1);
            return size == SystemIconSize.Large ?
                Icon.FromHandle(Large[0]) : Icon.FromHandle(Small[0]);
        }

        public static Icon IconFromExtensionShell(string extension, SystemIconSize size)
        {
            //add '.' if nessesry
            if (extension[0] != '.') extension = '.' + extension;

            //temp struct for getting file shell info
            SHFILEINFO fileInfo = new SHFILEINFO();

            SHGetFileInfo(
                extension,
                0,
                out fileInfo,
                Marshal.SizeOf(fileInfo),
                FileInfoFlags.SHGFI_ICON | FileInfoFlags.SHGFI_USEFILEATTRIBUTES | (FileInfoFlags)size);

            return Icon.FromHandle(fileInfo.hIcon);
        }

        public static Icon IconFromResource(string resourceName)
        {
            Assembly assembly = Assembly.GetCallingAssembly();

            return new Icon(assembly.GetManifestResourceStream(resourceName));
        }

        /// <summary>
        /// Parse strings in registry who contains the name of the icon and
        /// the index of the icon an return both parts.
        /// </summary>
        /// <param name="regString">The full string in the form "path,index" as found in registry.</param>
        /// <param name="fileName">The "path" part of the string.</param>
        /// <param name="index">The "index" part of the string.</param>
        public static void ExtractInformationsFromRegistryString(
            string regString, out string fileName, out int index)
        {
            if (regString == null)
            {
                throw new ArgumentNullException("regString");
            }
            if (regString.Length == 0)
            {
                throw new ArgumentException("The string should not be empty.", "regString");
            }

            index = 0;
            string[] strArr = regString.Replace("\"", "").Split(',');
            fileName = strArr[0].Trim();
            if (strArr.Length > 1)
            {
                int.TryParse(strArr[1].Trim(), out index);
            }
        }

        public static Icon ExtractFromRegistryString(string regString, SystemIconSize size)
        {
            string fileName;
            int index;
            ExtractInformationsFromRegistryString(regString, out fileName, out index);
            return ExtractOne(fileName, index, size);
        }
    }
}

Answer 2

Take a look at: http://mvolo.com/display-pretty-file-icons-in-your-aspnet-applications-with-iconhandler/

It's not the cleanest solution but it works. Otherwise, try to get your hands on a library of Icons that's based on mime type or file extension.