通过API在xamarin.ios中发送带有附件的电子邮件

Question

我需要在xamarin.ios中的“按钮单击”上发送带有附件的电子邮件。但是UIImage.FromFile（filename）返回null。图像是从api加载并内部存储的。

以下是代码：

   partial void SendMailBtn_TouchUpInside(UIButton sender)
        {


            var img = SelectedBook.image;

            if (MFMailComposeViewController.CanSendMail)
            {

                if (MFMailComposeViewController.CanSendMail)
                {
                    mailController = new MFMailComposeViewController();
                    mailController.SetToRecipients(to);
                    mailController.SetSubject(subject);
                    mailController.SetMessageBody(body, false);

                    var documentsDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
                    if (!string.IsNullOrEmpty(img))
                    {
                        string jpg = img + ".jpg";
                        string filename = System.IO.Path.Combine(documentsDirectory, img);
                        UIImage images = UIImage.FromFile(filename);
                        NSData imagedata = images.AsJPEG();
                        mailController.AddAttachmentData(imagedata, "image/jpeg", jpg);
                    }


                    mailController.Finished += (object s, MFComposeResultEventArgs args) => {

                        Console.WriteLine("result: " + args.Result.ToString()); // sent or cancelled

                        BeginInvokeOnMainThread(() => {
                            args.Controller.DismissViewController(true, null);
                        });
                    };
                }

                this.PresentViewController(mailController, true, null);
            }
            else
            {
                new UIAlertView("Mail not supported", "Can't send mail from this device", null, "OK");
            }
        }