asp.net mvc - 如何实现 IVirtualFileWithModifiedDate， ImageResize

我写了以下 ImageResizer 插件，但是当我更改原始图像时，除非删除imagecache文件夹，否则缓存的图像剂量不会改变。

public class MyImageResizerPlugin : IPlugin, IQuerystringPlugin, IVirtualImageProvider
{
    public bool FileExists(string virtualPath, NameValueCollection queryString)
    {
        string fileController = SmartizUrlHelpers.GetUrlHelperInstance().Action("Get", "File");
        return !string.IsNullOrWhiteSpace(fileController) && (virtualPath.StartsWith(fileController, StringComparison.OrdinalIgnoreCase));
    }
    public IVirtualFile GetFile(string virtualPath, NameValueCollection queryString)
    {
        return new GetImageFromVirtualFile(virtualPath, queryString);
    }
    public IEnumerable<string> GetSupportedQuerystringKeys()
    {
        return new[] { "maxwidth", "maxheight", "img" };
    }
    public IPlugin Install(Config c)
    {
        c.Plugins.add_plugin(this);
        return this;
    }
    public bool Uninstall(Config c)
    {
        c.Plugins.remove_plugin(this);
        return true;
    }
    public class GetImageFromVirtualFile : IVirtualFileWithModifiedDate
    {
        public GetImageFromVirtualFile(string virtualPath, NameValueCollection query)
        {
            uint maxwidth, maxheight;
            uint.TryParse(query["maxwidth"], out maxwidth);
            uint.TryParse(query["maxheight"], out maxheight);
            ResizeSettings resizeSettings = new ResizeSettings();
            if (maxwidth > 0) resizeSettings.MaxWidth = (int)maxwidth;
            if (maxheight > 0) resizeSettings.MaxHeight = (int)maxheight;
            this.ResizeSettings = resizeSettings;
            VirtualPath = virtualPath;
        }
        public string VirtualPath { get; private set; }
        protected ResizeSettings ResizeSettings;
        public Stream Open()
        {
            long id;
            string idString = Regex.Replace(VirtualPath, @"'D", "");
            if (!long.TryParse(idString, out id)) return null;
            Attachment attachment = new SmartService().GetAttachmentById(id);
            if (attachment == null) return null;
            MemoryStream memoryStream = new MemoryStream();
            string absoluteFilePath = UploadedPaths.GetAbsolutePath(attachment.Path);
            if (!File.Exists(absoluteFilePath)) throw new HttpException(404, "404 error");
            using (FileStream file = new FileStream(absoluteFilePath, FileMode.Open, FileAccess.Read))
            {
                byte[] bytes = new byte[file.Length];
                file.Read(bytes, 0, (int)file.Length);
                memoryStream.Write(bytes, 0, (int)file.Length);
            }
            memoryStream.Seek(0, SeekOrigin.Begin);
            return memoryStream;
        }
        public DateTime ModifiedDateUTC { get; private set; }
    }
}

我认为我没有正确实现IVirtualFileWithModifiedDate。 ModifiedDateUTC

你能指导我吗？