如何在 C# 中的 foreach 循环中构建失败的电子邮件列表

Question

I am trying to check Email validation for list of mails. If any of the emails are invalid, i have to send the list of failed mail validations with false message, I am very new to C#, how can we achieve this? when i am reading books i found it is possible through StringBuilder, but i am unable to find the syntax for this, can any please provide the syntax for this.

    public static string IsSMTPRequestValid(this SmtpGatewayRequest smtpRequest)
            {

                SmtpRequestContent content = smtpRequest.Body as SmtpRequestContent;

                foreach (string email in content.EmailCC)
                {
                    bool valid = IsEmail(email);
/* Here I would like to check in any of the mails are invalid I have to return false, with the list of invalid mails.*/
                }

            }

Thanks a lot in advance.

Answer 1

First you have to create instance of StringBuilder class and then just append all invalid emails to it in new lines. If you want to return all emails in string you have to call .ToString() method.

public static string IsSMTPRequestValid(this SmtpGatewayRequest smtpRequest)
{
    StringBuilder invalidEmails = new StringBuilder();
    SmtpRequestContent content = smtpRequest.Body as SmtpRequestContent;

    content.EmailCC.Where(email => !IsEmail(email))
        .ForEach(n =>
        {
            invalidEmails.AppendLine(n)
        });
    return invalidEmails.ToString();
}

or in easier-to-understand form

public static string IsSMTPRequestValid(this SmtpGatewayRequest smtpRequest)
{
    StringBuilder invalidEmails = new StringBuilder();
    SmtpRequestContent content = smtpRequest.Body as SmtpRequestContent;

    foreach (var email in content.EmailCC)
    {
        if (!IsEmail(email))
        {
            invalidEmails.AppendLine(email);
        }
    }

    return invalidEmails.ToString();
}

Moving away from this solutions i think that the best solution would be to return the entire list of items. For example:

public static List<string> IsSMTPRequestValid(this SmtpGatewayRequest smtpRequest)
{
    List<string> invalidEmails = new List<string>();
    SmtpRequestContent content = smtpRequest.Body as SmtpRequestContent;

    foreach (var email in content.EmailCC)
    {
        if (!IsEmail(email))
        {
            invalidEmails.Add(email);
        }
    }

    return invalidEmails;
}