找不到文件...。Web应用程序文件夹中已存在任何文件

Question

我有一个Web应用程序，用于向订阅者发送电子邮件。现在我在从Web应用程序文件夹访问图像文件时遇到一些问题。这是我的代码：

string fbody = plainText.Replace("\"", "'");
        if (fbody.Contains("src='cid:"))
        {
            var htmlView = AlternateView.CreateAlternateViewFromString(msg.Body, null, "text/html");
            do
            {
                int src = fbody.IndexOf("src='cid:");
                if (src != -1)
                {
                    fbody = fbody.Remove(0, src + 9);
                    var dot = Regex.Match(fbody, @"\.(jpg|jpeg|gif|png)");
                    if (dot.Success)
                    {
                        int comma = fbody.IndexOf("'");
                        if (comma != -1)
                        {
                            if (!string.IsNullOrEmpty(fbody.Substring(0, comma)))
                            {
                                string imageSource = Path.Combine(HttpRuntime.AppDomainAppPath, "EmailFiles/" + fbody.Substring(0, comma));  // here I got image file 
                                var leftImageLink = (dynamic)null;
                                switch (Path.GetExtension(imageSource).ToLower())
                                {
                                    case ".jpg":
                                        leftImageLink = new LinkedResource(imageSource, "image/jpg") // here error thrown could not access file
                                        {
                                            ContentId = fbody.Substring(0, comma),
                                            TransferEncoding = System.Net.Mime.TransferEncoding.Base64
                                        };
                                        break;
                                    case ".jpeg":
                                        leftImageLink = new LinkedResource(imageSource, "image/jpeg")
                                        {
                                            ContentId = fbody.Substring(0, comma),
                                            TransferEncoding = System.Net.Mime.TransferEncoding.Base64
                                        };
                                        break;
                                    case ".gif":
                                        leftImageLink = new LinkedResource(imageSource, "image/gif")
                                        {
                                            ContentId = fbody.Substring(0, comma),
                                            TransferEncoding = System.Net.Mime.TransferEncoding.Base64
                                        };
                                        break;
                                    case ".png":
                                        leftImageLink = new LinkedResource(imageSource, "image/png")
                                        {
                                            ContentId = fbody.Substring(0, comma),
                                            TransferEncoding = System.Net.Mime.TransferEncoding.Base64
                                        };
                                        break;
                                }
                                htmlView.LinkedResources.Add(leftImageLink);
                            }
                        }
                    }
                }
            }
            while (fbody.Contains("src='cid:"));
            msg.AlternateViews.Add(htmlView);

这里出了什么问题。我在imagesource获得文件，但没有leftImageLink。这里出了什么问题???