How to create custom validation attribute for MVC

Question

I'd like to create a custom validation attribute for MVC2 for an email address that doesn't inherit from RegularExpressionAttribute but that can be used in client validation. Can anyone point me in the right direction?

I tried something as simple as this:

[AttributeUsage( AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false )]
public class EmailAddressAttribute : RegularExpressionAttribute
{
    public EmailAddressAttribute( )
        : base( Validation.EmailAddressRegex ) { }
}

but it doesn't seem to work for the client. However, if I use RegularExpression(Validation.EmailAddressRegex)] it seems to work fine.

Answer 1

Have you tried using Data Annotations?

This is my Annotations project using System.ComponentModel.DataAnnotations;

public class IsEmailAddressAttribute : ValidationAttribute
{
  public override bool IsValid(object value)
  {
    //do some checking on 'value' here
    return true;
  }
}

This is in my Models project

namespace Models
{
    public class ContactFormViewModel : ValidationAttributes
    {
        [Required(ErrorMessage = "Please provide a short message")]
        public string Message { get; set; }
    }
}

This is my controller

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult ContactUs(ContactFormViewModel formViewModel)
{
  if (ModelState.IsValid)
  {
    RedirectToAction("ContactSuccess");
  }

  return View(formViewModel);
}

You'll need to google DataAnnotations as you need to grab the project and compile it. I'd do it but I need to get outta here for a long w/end.

Hope this helps.

EDIT

Found this as a quick google.

Answer 2

I would suggest you checking Phil Haacks excellent post about validation.