IconExtractor

This is an example how to retrieve an icon for a file class without a file.

Reference: MSDN/HOWTO: Retrieve an Icon for a File Class Without a File

Downloads

  IconExtractor.cs - C# source file
  IconExtractor.zip - C# demo soulution

Explanation

For retrieving an icon for a file class without a file we use a Shell32.dll library.

First of all we should to import a function that will return a handle to the required icon.

[DllImport("Shell32.dll")]
private static extern IntPtr SHGetFileInfo(
    string pszPath,
    uint dwFileAttributes,
    out SHFILEINFO psfi,
    uint cbfileInfo,
    SHGFI uFlags );

where SHFILEINFO is a structure that has the next definition:

[StructLayout(LayoutKind.Sequential)]
private enum SHGFI
{
    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
}

// Get icon for existing file or for file type (by extension like '*.txt')
public static Icon GetIcon( string strPath, bool small, bool selected )
{
    SHFILEINFO shfi = new SHFILEINFO(true);
    
    int cbFileInfo = Marshal.SizeOf(shfi);

    // To do this, select the SHGFI_USEFILEATTRIBUTES flag
    // so that the API assumes that the file exists
    // and it will not try to look for it on disk.
    SHGFI flags = SHGFI.SHGFI_USEFILEATTRIBUTES|SHGFI.SHGFI_ICON;

    if( selected )
        flags |= SHGFI.SHGFI_OPENICON;

    if( small )
        flags |= SHGFI.SHGFI_SMALLICON;

    SHGetFileInfo( strPath,
        256,
        out shfi,
        (uint)cbFileInfo,
        flags );
    
    return Icon.FromHandle( shfi.hIcon );
}

Thanks: Oleg Axenow