How to call Async Method within Task.Run? [duplicate]

问题

I need to send mail in Async way. I have figured out to use Razor Generator to generate Html template from razor view. now i need to use SmtpClient.SendMailAsync to send the html as Mail. but i found Razor generator takes quite some time and i do not want to include the template generation part inside my send mail method as the send mail method should not be concerned about getting the Html Template.

I have sample code:

public static void SendEmailAsync<TModel>(TModel model, string templatePath, string subj, string toEmail, string cc = null, string bcc = null)
    {

        string templateFilePath = HostingEnvironment.MapPath(templatePath);
        // Generate the email body from the template file.
        // 'templateFilePath' should contain the absolute path of your template file.
        if (templateFilePath != null)
        {
            Task.Run(() =>
            {
                var emailHtmlBody = Engine.Razor.RunCompile(File.ReadAllText(templateFilePath),
                templateFilePath, model.GetType(), model);
                SendEmailAsync(subj, emailHtmlBody, toEmail, cc, bcc);
            });
        }
        else
        {
            throw new System.Exception("Could not find mail template.");
        }
    }

and the signature for SendMailAsync Is:

static async Task SendEmailAsync(string subj, string message, string toEmail, string cc = null, string bcc = null)
    {
        //Reading sender Email credential from web.config file  
        string fromEmail = ConfigurationManager.AppSettings["FromEmail"].ToString();
        string fromName = ConfigurationManager.AppSettings["FromName"].ToString();

        //creating the object of MailMessage  
        MailMessage mailMessage = new MailMessage();
        mailMessage.From = new MailAddress(fromEmail, fromName); //From Email Id  
        mailMessage.Subject = subj; //Subject of Email  
        mailMessage.Body = message; //body or message of Email  
        mailMessage.IsBodyHtml = true;

        string[] toMuliId = toEmail.Split(',');
        foreach (string toEMailId in toMuliId)
        {
            mailMessage.To.Add(new MailAddress(toEMailId)); //adding multiple TO Email Id  
        }


        if (cc != null)
        {
            string[] ccId = cc.Split(',');

            foreach (string ccEmail in ccId)
            {
                mailMessage.CC.Add(new MailAddress(ccEmail)); //Adding Multiple CC email Id  
            }
        }

        if (bcc != null)
        {
            string[] bccid = bcc.Split(',');

            foreach (string bccEmailId in bccid)
            {
                mailMessage.Bcc.Add(new MailAddress(bccEmailId)); //Adding Multiple BCC email Id  
            }
        }

        SmtpClient smtp = new SmtpClient
        {
            EnableSsl = true,
            Credentials = new NetworkCredential("", "")
        };

        //network and security related credentials  
        await smtp.SendMailAsync(mailMessage); //sending Email  
    }

No exceptions are thrown but i get the error:

System.InvalidOperationException: An asynchronous operation cannot be started at this time. Asynchronous operations may only be started within an asynchronous handler or module or during certain events in the Page lifecycle. If this exception occurred while executing a Page, ensure that the Page is marked <%@ Page Async="true" %>. This exception may also indicate an attempt to call an "async void" method, which is generally unsupported within ASP.NET request processing. Instead, the asynchronous method should return a Task, and the caller should await it.

回答1:

Use this:

await Task.Run(async () =>
{
    await DoAsyncMethodAsync();
});

回答2:

This issue is that you are running the following method every time an email is sent (this generates the initial class which takes time)

Engine.Razor.RunCompile

Ideally, you should be calling the following method and only then, if that throws an error, then calling RunCompile

Engine.Razor.Run

See this article on using a Template Manager with Caching

来源：https://stackoverflow.com/questions/39071826/how-to-call-async-method-within-task-run

标签

asp.net-mvc

asynchronous

async-await

sendmail