How do you access the Windows ThumbnailCache in WPF?

I'm trying to make use of Window's ThumbnailCache in a WPF application. I'm starting with a path to an image file and hoping to end up with a Media.Imaging.BitmapImage that holds the thumbnail.

I've been piecing things together, but I'm starting to think I'm on the wrong track. This feels like a lot of code to do what ought to be straightforward.

Am I on the wrong track with this?

    public BitmapImage Thumbnail { get; set; }

    private void LoadThumbnail()
    {
        IShellItem shellItem;
        SHCreateItemFromParsingName(FilePath, IntPtr.Zero, typeof(IShellItem).GUID, out shellItem);

        IntPtr hBitmap = IntPtr.Zero;
        ((IShellItemImageFactory)shellItem).GetImage(new SIZE(256, 256), 0x0, out hBitmap);

        try
        {
            BitmapSource bitmapSource = System.Windows.Interop.Imaging.CreateBitmapSourceFromHBitmap(
                hBitmap,
                IntPtr.Zero,
                Int32Rect.Empty,
                BitmapSizeOptions.FromEmptyOptions());

            BitmapImage bitmapImage = new BitmapImage();

            ??? BitmapImage from BitmapSource...

            Thumbnail = bitmapImage;
        }
        finally
        {
            DeleteObject(hBitmap);
        }
    }




    [DllImport("shell32.dll", CharSet = CharSet.Unicode, PreserveSig = false)]
    public static extern void SHCreateItemFromParsingName(
        [In][MarshalAs(UnmanagedType.LPWStr)] string pszPath,
        [In] IntPtr pbc,
        [In][MarshalAs(UnmanagedType.LPStruct)] Guid riid,
        [Out][MarshalAs(UnmanagedType.Inte开发者_如何学Gorface, IidParameterIndex = 2)] out IShellItem ppv);

    [ComImportAttribute()]
    [GuidAttribute("bcc18b79-ba16-442f-80c4-8a59c30c463b")]
    [InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IShellItemImageFactory
    {
        void GetImage(
        [In, MarshalAs(UnmanagedType.Struct)] SIZE size,
        [In] SIIGBF flags,
        [Out] out IntPtr phbm);
    }

    [ComImport]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    [Guid("43826d1e-e718-42ee-bc55-a1e261c37bfe")]
    public interface IShellItem
    {
        void BindToHandler(IntPtr pbc,
            [MarshalAs(UnmanagedType.LPStruct)]Guid bhid,
            [MarshalAs(UnmanagedType.LPStruct)]Guid riid,
            out IntPtr ppv);

        void GetParent(out IShellItem ppsi);

        void GetDisplayName(SIGDN sigdnName, out IntPtr ppszName);

        void GetAttributes(uint sfgaoMask, out uint psfgaoAttribs);

        void Compare(IShellItem psi, uint hint, out int piOrder);
    };

    [StructLayout(LayoutKind.Sequential)]
    public struct SIZE
    {
        public int cx;
        public int cy;

        public SIZE(int cx, int cy)
        {
            this.cx = cx;
            this.cy = cy;
        }
    }

    [Flags]
    public enum SIIGBF
    {
        SIIGBF_RESIZETOFIT = 0x00,
        SIIGBF_BIGGERSIZEOK = 0x01,
        SIIGBF_MEMORYONLY = 0x02,
        SIIGBF_ICONONLY = 0x04,
        SIIGBF_THUMBNAILONLY = 0x08,
        SIIGBF_INCACHEONLY = 0x10,
    }

    public enum SIGDN : uint
    {
        NORMALDISPLAY = 0,
        PARENTRELATIVEPARSING = 0x80018001,
        PARENTRELATIVEFORADDRESSBAR = 0x8001c001,
        DESKTOPABSOLUTEPARSING = 0x80028000,
        PARENTRELATIVEEDITING = 0x80031001,
        DESKTOPABSOLUTEEDITING = 0x8004c000,
        FILESYSPATH = 0x80058000,
        URL = 0x80068000
    }

    [System.Runtime.InteropServices.DllImport("gdi32.dll")]
    public static extern bool DeleteObject(IntPtr hObject);

There is an open source library for reading thumbs.db files available here:

http://www.petedavis.net/drupal//index.php?q=node/2

It includes full sourcecode. Might be easier than trying to do-it-yourself!