如何为Windows Vista编写有效的IThumbnailProvider

using System;
using System.Runtime.InteropServices;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;

[Guid("49C975B0-A1C0-420C-8A2F-DFD42F8D1B9E")]
public class MyThumbnailProvider : IThumbnailProvider
{
    public int GetThumbnail(uint cx, out IntPtr phbmp, out WTS_ALPHATYPE pdwAlpha)
    {
        phbmp = IntPtr.Zero;
        pdwAlpha = WTS_ALPHATYPE.WTSAT_UNKNOWN;

        // 生成缩略图
        Bitmap bitmap = new Bitmap(cx, cx);
        Graphics graphics = Graphics.FromImage(bitmap);
        graphics.Clear(Color.White);
        graphics.DrawString("Thumbnail", new Font("Arial", 12), Brushes.Black, 0, 0);

        // 将缩略图转换为HBITMAP
        phbmp = bitmap.GetHbitmap();
        pdwAlpha = WTS_ALPHATYPE.WTSAT_RGB;

        return 0;
    }
}