c# - ASP.NET MVC 中回调后的 RedirectToAction

Question

我想在完成一些任务(发送电子邮件)后重定向到操作，但我不知道如何正确地做到这一点。

这是我的代码，但是 RedirectToAction 在这里没有做任何事情!

[HttpPost]
public ActionResult SendEmail(EmailContentViewModel emailDetails)
{
    using (MailMessage email = new MailMessage(emailDetails.from, emailDetails.to))
    {
        email.Subject = emailDetails.subject;
        email.Body = emailDetails.body;
        email.Priority = emailDetails.MailPriority;

        processSendingEmail(email, (result) =>
        {
            RedirectToAction("ContactResult", "Contact", new { success = result }); //It's not redirecting to the ContactResult page!
        });
    }

    return null;
}

---

private void processSendingEmail(MailMessage email, Action<bool> callback= null)
    {
        using (SmtpClient smtpClient = new SmtpClient(_smtpHostName, _smtpPort))
        {
            bool sentSuccessfully = false;

            try
            {
               //.............//
            }
            catch(Exception e)
            {
               //.............//
            }

            callback?.Invoke(sentSuccessfully);
        }
    }

---

基于 Panagiotis Kanavos's response ，这是一个工作代码:

    [HttpPost]
    public async Task<ActionResult> SendEmail(EmailContentViewModel emailDetails)
    {
        using (MailMessage email = new MailMessage(emailDetails.from, emailDetails.to))
        {
            email.Subject = emailDetails.subject;
            email.Body = emailDetails.body;
            email.Priority = emailDetails.MailPriority;

            var sentSuccessfully= await processSendingEmail(email);

            return RedirectToAction("ContactResult", "Contact", new { success = sentSuccessfully});
        }
    }


    private async Task<bool> processSendingEmail(MailMessage email)
    {
        var client = new MailKit.Net.Smtp.SmtpClient();
        //Configure the client here ...
        try
        {
            var msg = (MimeKit.MimeMessage)email;
            await client.SendAsync(msg);
            return true;
        }
        catch (Exception ex)
        {
            Debug.Fail(ex.Message);
            string errorMessage = "";
            switch (ex)
            {
                case SmtpFailedRecipientException f:
                    errorMessage = $"Failed to send to {f.FailedRecipient}";
                    break;
                case SmtpException s:
                    errorMessage = "Protocol error";
                    break;
                default:
                    errorMessage = "Unexpected error";
                    break;
            }

            //Do anything you want with the error message

            return false;
        }
    }

Answer 1

不要使用回调。 RedirectToAction 创建一个应由操作返回的 ActionResult，它不会强制重定向。

异步执行某些操作的正确方法是使用 async/await。即使您的电子邮件库没有基于任务的异步方法，您也可以使用 TaskCompletionSource 使其适应基于任务的模型。这将是相当不寻常的，因为大多数库已经从旧的异步模型(如回调、事件和 APM)转移到任务。

MailMessage 表明您正在使用 SmtpClient . SendMailAsync方法是基于任务的，这意味着你可以写

await client.SendMailAsync(email);

例如:

[HttpPost]
public async Task<ActionResult> SendEmail(EmailContentViewModel emailDetails)
{
    SmptClient client = ... //Configure the client here
    using (MailMessage email = new MailMessage(emailDetails.from, emailDetails.to))
    {
        email.Subject = emailDetails.subject;
        email.Body = emailDetails.body;
        email.Priority = emailDetails.MailPriority;

        await client.SendMailAsync(email);
        return RedirectToAction("ContactResult", "Contact", new { success = true }); 
    };
}

不过，SmptClient 是一个过时的类。它的文档页面警告说:

We don't recommend that you use the SmtpClient class for new development. For more information, see SmtpClient shouldn't be used on GitHub.

该链接解释说:

SmtpClient doesn't support many modern protocols. It is compat-only. It's great for one off emails from tools, but doesn't scale to modern requirements of the protocol.

建议使用较新的库，如 MailKit

MailKit 允许将 MailMessage 显式转换为 MimeMessage，这使得将现有代码转换为 MailKit 变得容易:

[HttpPost]
public async Task<ActionResult> SendEmail(EmailContentViewModel emailDetails)
{
    var client = new MailKit.Net.Smtp.SmptClient();
    /Configure the client here ...
    using (MailMessage email = new MailMessage(emailDetails.from, emailDetails.to))
    {
        email.Subject = emailDetails.subject;
        email.Body = emailDetails.body;
        email.Priority = emailDetails.MailPriority;

        var msg=(MailKit)email;
        await client.SendAsync(msg);
        return RedirectToAction("ContactResult", "Contact", new { success = true }); 
    };
}

错误处理

MailKit 和旧的 SmptClient 的 Send 方法都成功或抛出。一种选择是隐藏异常并返回真/假成功标志:

try
{
    await client.SendAsync(msg);
    return RedirectToAction("ContactResult", "Contact", new { success = true});
}
catch
{
    return RedirectToAction("ContactResult", "Contact", new { success = false});
}

但这对尝试诊断可能问题的用户或管理员来说不是很有帮助。这些方法的文档解释了可能发生的异常类型，例如:ArgumentNullException 表示空消息、InvalidOperationException、SmtpFailedRecipientException 等等。

至少，代码可以在返回失败之前记录异常:

catch(Exception ex)
{
    _log.Error(ex);
    return RedirectToAction("ContactResult", "Contact", new { success = false});
}

一个更好的主意是处理特定的异常并可能警告用户:

catch(SmtpFailedRecipientException ex)
{
    _log.Error(ex);
    return RedirectToAction("ContactResult", "Contact", new { success = false,message=$"Couldn't send the message to {ex.FailedRecipient}"});
}
catch(SmtpException ex)
{
    _log.Error(ex);
    return RedirectToAction("ContactResult", "Contact", new { success = false,message="Failed to send the message"});
}
catch(Exception ex)
{
    _log.Error(ex);
    return RedirectToAction("ContactResult", "Contact", new { success = false,message="An unexpected error occured"});
}

C# 7 中的模式匹配使这更容易:

catch(Exception ex)
{
    _log.Error(ex);
    string message="";
    switch (ex)
    {
        case SmtpFailedRecipientException f:
            message=$"Failed to send to {f.FailedRecipient}"; 
            break;
        case SmptException s :
            message="Protocol error";
            break;
        default:
            message="Unexpected error";
            break;
    }
    return RedirectToAction("ContactResult", "Contact", new { success = false,message=message});
}

分离方法

将发送代码重构为单独的方法很容易。 try/catch block 和客户端声明可以提取到单独的方法中:

async Task<string> MySendMethod(MailMessage email)
{
    var client = new MailKit.Net.Smtp.SmptClient();
    //Configure the client here ...
    try
    {
        var msg=(MailKit)email;
        await client.SendAsync(msg);
        return "";
    }
    catch(Exception ex)
    {
        _log.Error(ex);
        switch (ex)
        {
            case SmtpFailedRecipientException f:
                return $"Failed to send to {f.FailedRecipient}"; 
            case SmptException s :
                return "Protocol error";
            default:
                return "Unexpected error";
        }
    }
}

该方法不返回 RedirectToActionResult，而是返回结果字符串。如果为空，则操作成功。 Controller Action 可以这样重写:

[HttpPost]
public async Task<ActionResult> SendEmail(EmailContentViewModel emailDetails)
{
    using (MailMessage email = new MailMessage(emailDetails.from, emailDetails.to))
    {
        email.Subject = emailDetails.subject;
        email.Body = emailDetails.body;
        email.Priority = emailDetails.MailPriority;

        var message=await MySendMethod(email);
        return RedirectToAction("ContactResult", "Contact", 
                   new { success = String.IsNullOrWhitespace(result),
                         message=message 
                   }); 
    };
}