Live Fast, Code Hard, Die Young

Recently I wanted to show shell icons in a custom control on a Windows form. The custom control only supported bitmaps so I needed to convert the icons into bitmaps. This is quite easy in .NET since there is a nice Bitmap.FromHIcon() method. The problem is that when you use this method the icon transparency is lost, at least when you use it to extract shell icons (using the SHGetFileInfo API).
 
I tried to search for a solution but wasn’t able to locate any so I decided to fiddle around a bit on my own. Here is the way I came up with that works.
 

SHFILEINFO fi;

SHGetFileInfo(filename, 0, out fi, Marshal.SizeOf(typeof(SHFILEINFO)), FileInfoFlags.SHGFI_ICON | FileInfoFlags.SHGFI_SMALLICON);

using (Icon icon = Icon.FromHandle(fi.hIcon)) {

    Bitmap bm = new Bitmap(icon.Size.Width, icon.Size.Height);

    using (Graphics g = Graphics.FromImage(bm))

        g.DrawIcon(icon, 0, 0);

    return bm;

}

 

In other words, the solution is to draw the icon on an existing bitmap. The draw method will consider the transparency information when drawing which is what we want.
 
Here is the full class for retrieving a shell file icon as a bitmap:
 

public class FileInfoHelper {

 

    struct SHFILEINFO {

        public IntPtr hIcon;

        public int iIcon;

        public int dwAttributes;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]

        public string szDisplayName;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 80)]

        public string szTypeName;

    }

 

    [Flags]

    enum FileInfoFlags : int {

        SHGFI_ICON = 0x000000100,    // get icon

        SHGFI_DISPLAYNAME = 0x000000200,    // get display name

        SHGFI_TYPENAME = 0x000000400,    // get type name

        SHGFI_ATTRIBUTES = 0x000000800,    // get attributes

        SHGFI_ICONLOCATION = 0x000001000,    // get icon location

        SHGFI_EXETYPE = 0x000002000,    // return exe type

        SHGFI_SYSICONINDEX = 0x000004000,    // get system icon index

        SHGFI_LINKOVERLAY = 0x000008000,    // put a link overlay on icon

        SHGFI_SELECTED = 0x000010000,    // show icon in selected state

        SHGFI_ATTR_SPECIFIED = 0x000020000,    // get only specified attributes

        SHGFI_LARGEICON = 0x000000000,    // get large icon

        SHGFI_SMALLICON = 0x000000001,    // get small icon

        SHGFI_OPENICON = 0x000000002,    // get open icon

        SHGFI_SHELLICONSIZE = 0x000000004,    // get shell size icon

        SHGFI_PIDL = 0x000000008,    // pszPath is a pidl

        SHGFI_USEFILEATTRIBUTES = 0x000000010,    // use passed dwFileAttribute

        SHGFI_ADDOVERLAYS = 0x000000020,    // apply the appropriate overlays

        SHGFI_OVERLAYINDEX = 0x000000040,    // Get the index of the overlay in

        // the upper 8 bits of the iIcon

    }

 

    [DllImport("shell32.dll", CharSet = CharSet.Auto)]

    static extern Int64 SHGetFileInfo(string pszPath, int dwFileAttributes, out SHFILEINFO psfi, int cbFileInfo, FileInfoFlags uFlags);

 

    /// <summary>

    /// Creates a new bitmap with the small icon for a file.

    /// </summary>

    /// <param name="filename"></param>

    /// <returns></returns>

    public static Bitmap GetFileIconAsBitmap(string filename) {

        SHFILEINFO fi;

        SHGetFileInfo(filename, 0, out fi, Marshal.SizeOf(typeof(SHFILEINFO)), FileInfoFlags.SHGFI_ICON | FileInfoFlags.SHGFI_SMALLICON);

        using (Icon icon = Icon.FromHandle(fi.hIcon)) {

            Bitmap bm = new Bitmap(icon.Size.Width, icon.Size.Height);

            using (Graphics g = Graphics.FromImage(bm))

                g.DrawIcon(icon, 0, 0);

            return bm;

        }

    }

}

 

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