将 .jpg 图像（base64 字符串表示）嵌入电子邮件正文（System.Net.Mail）

Question

我能够正确地将 jpg 图像转换为 base64String。但我无法使用转换后的图像字符串和 LinkedResource 将其嵌入到电子邮件正文中。该图像在电子邮件正文中显示为“未找到图像”图标。 任何帮助将不胜感激。

我已按照此链接中的示例进行操作：Iterate through an html string to find all img tags and replace the src attribute values

我正在使用 HtmlAgilityPack（nuget 包）通过以下代码定位 img 元素。

private string embedImageInMail(string html)
       {
            HtmlAgilityPack.HtmlDocument doc = new 
HtmlAgilityPack.HtmlDocument();
            doc.LoadHtml(html);
            doc.DocumentNode.Descendants("img").Where(e =>
            {
                string src = e.GetAttributeValue("src", null) ?? "";
                return !string.IsNullOrEmpty(src) && src.StartsWith("data:image");
            })
            .ToList()
            .ForEach(x =>
            {
                string currentSrcValue = x.GetAttributeValue("src", null);
                currentSrcValue = currentSrcValue.Split(',')[1];    //Base64 part of string
                byte[] imageData = Convert.FromBase64String(currentSrcValue);
                string contentId = Guid.NewGuid().ToString();
                using (MemoryStream ms = new MemoryStream(imageData))
                {
                    LinkedResource inline = new LinkedResource(ms, "image/jpeg");
                    inline.ContentId = contentId;
                    inline.TransferEncoding = System.Net.Mime.TransferEncoding.Base64;
                    x.SetAttributeValue("src", "cid:" + inline.ContentId);
                }
            });

        return doc.DocumentNode.OuterHtml; 
    }

传递给函数的 html 参数包含一个 img 标签，其 src 等于图像的 base64 编码。 从此函数返回的内容被分配给电子邮件的 message.body。

Answer 1

通过以下其他帖子中的解决方案解决。如果有其他人尝试做同样的事情并且像我一样遇到麻烦，我将在下面发布代码。

基本上，我必须将 html 中的 LinkedResource（图像）保存到一个列表中，然后遍历该列表并将所有图像添加到 foreach 循环之外的 AlternateView。

 // Embeds image to properly show in Email. Image element to show in html will not work in Email body. 
                        // https://stackoverflow.com/questions/39785600/iterate-through-an-html-string-to-find-all-img-tags-and-replace-the-src-attribut
                        // XmlAgilityPack gets used here to parse html string. 
                        List<LinkedResource> linkedResources = new List<LinkedResource>(); 
                        HtmlAgilityPack.HtmlDocument doc = new HtmlAgilityPack.HtmlDocument();
                        int increment = 0; 
                        doc.LoadHtml(tempMsg);
                        doc.DocumentNode.Descendants("img").Where(z =>
                            {
                                string src = z.GetAttributeValue("src", null) ?? "";
                                return !string.IsNullOrEmpty(src) && src.StartsWith("data:image");
                            })
                            .ToList()
                            .ForEach(x =>
                            {
                                string currentSrcValue = x.GetAttributeValue("src", null);
                                currentSrcValue = currentSrcValue.Split(',')[1];    //Base64 part of string
                                byte[] imageData = Convert.FromBase64String(currentSrcValue);
                                string id = Guid.NewGuid().ToString();
                                increment++;

                                LinkedResource inlineImage = new LinkedResource(new MemoryStream(imageData), System.Net.Mime.MediaTypeNames.Image.Jpeg);
                                inlineImage.ContentType.Name = "img " + increment; 
                                inlineImage.ContentId = id;
                                inlineImage.TransferEncoding = System.Net.Mime.TransferEncoding.Base64;
                                x.SetAttributeValue("src", "cid:" + inlineImage.ContentId);
                                linkedResources.Add(inlineImage);
                            });

                        // Append multiple images from template to email message.
                        // https://stackoverflow.com/questions/7048758/how-to-embed-multiple-images-in-email-body-using-net
                        // Write html to message.body 
                        AlternateView altView = AlternateView.CreateAlternateViewFromString(doc.DocumentNode.OuterHtml, null, "text/html");
                        linkedResources.ForEach(x=>altView.LinkedResources.Add(x));
                        message.AlternateViews.Add(altView);

                        String[] attachments = txtAttachFiles.Text.Split(';');
                        foreach (String filename in attachments)
                        {
                            if (File.Exists(filename))
                            {
                                Attachment attachment = new Attachment(filename);
                                message.Attachments.Add(attachment);
                            }
                        }

                        // loop is set to 1 in the app.config file so technically this for loop is not needed, but will keep this loop just in case. 
                        for (int loop = 0; loop < Convert.ToInt32(ConfigurationManager.AppSettings["loop"]); loop++)
                        {
                            SmtpClient smtp = new SmtpClient();
                            smtp.Host = ConfigurationManager.AppSettings["mailHost"];
                            smtp.Port = Int32.Parse(ConfigurationManager.AppSettings["mailPort"]);
                            smtp.UseDefaultCredentials = Convert.ToBoolean(ConfigurationManager.AppSettings["mailDefaultCredentials"]);
                            smtp.Send(message);
                        }
                    }