ASP.NET MVC 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 在这里什么也没做！

[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，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

使用基于任务的 ActionResult 而不是回调

[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 result = await processSendingEmail(email);
       return RedirectToAction("ContactResult", "Contact", new { success = result }); 
   }
}

async Task<bool> processSendingEmail(System.Net.Mail.MailMessage email) {            
    await Task.Delay(1000); //email code here...
    return true;
}

Answer 2

不要使用回调。 RedirectToAction 创建一个应由操作 return 编辑的 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 建议你使用 SmtpClient. The 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 }); 
    };
}

SmptClient 已过时 class。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.

link 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，例如 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 方法要么成功，要么抛出异常。一种选择是隐藏异常和 return 一个 true/false 成功标志：

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

尽管如此，这对试图诊断可能出现的问题的用户或管理员来说并不是很有帮助。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 returning 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});
}

分离法

将发送代码重构为单独的方法很容易。 try/catch 块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";
        }
    }
}

而不是 returning RedirectToActionResult，方法 returns 一个结果字符串。如果为空，则操作成功。控制器动作可以这样重写：

[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 
                   }); 
    };
}

ASP.NET MVC 回调后的 RedirectToAction

RedirectToAction after callback in ASP.NET MVC

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