MVC: Custom attribute not populating in view - asp.net-mvc

Question

I am writing a custom attribute to validate that a first and last name does not exceed a certain amount of characters, but the error message is not displaying like it does for out-of-the-box annotations.
Here is my implementation.
public class User
{
[Required(ErrorMessage = "Last Name is required.")]
[RegularExpression(#"^[a-zA-Z'\s]{1,50}$", ErrorMessage = "Please enter a valid last name.")]
[FullNameMaxLength("FirstName")]
public string LastName { get; set; }
}
public class FullNameMaxLengthAttribute : ValidationAttribute
{
private string _firstName;
public FullNameMaxLengthAttribute(string firstName)
{
_firstName = firstName;
}
protected override ValidationResult IsValid(object lastName, ValidationContext validationContext)
{
clsUserRegistration userRegistrationContext = (clsUserRegistration)validationContext.ObjectInstance;
if (lastName != null)
{
string strValue = lastName.ToString();
PropertyInfo propInfo = validationContext.ObjectType.GetProperty(_firstName);
if (propInfo == null)
return new ValidationResult(String.Format("Property {0} is undefined.", _firstName));
var fieldValue = propInfo.GetValue(validationContext.ObjectInstance, null).ToString();
if (strValue.Length + fieldValue.Length > 53)
{
return new ValidationResult("First and last names are too long!");
}
return ValidationResult.Success;
}
return null;
}
}
In my view, I have a ValidationMessageFor, and it works fine with non-custom attributes. When I step through my model, it returns the ValidationMessage, but I cannot see that error message. Any thoughts?

Answer 1

The above is just the "back-end" validation. This for example does still work when user's browser has JavaScript turned off - the page will post back regardless of errors but then show the form again with validation messages on it.
For "front-end" validation, you need something along these lines:
public class FullNameMaxLengthAttribute : ValidationAttribute, IClientValidatable
{
// Your Properties and IsValid method here
public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
{
var rule = new ModelClientValidationRule
{
ErrorMessage = String.IsNullOrEmpty(ErrorMessage) ? FormatErrorMessage(metadata.DisplayName) : ErrorMessage,
ValidationType = "fullnamemaxlength"
};
rule.ValidationParameters["firstname"] = FirstName;
rule.ValidationParameters["maxlength"] = 53;
yield return rule;
}
}
And then in JavaScript that is added to the page:
if (jQuery.validator) {
jQuery.validator.addMethod("fullnamemaxlength", function(value, element, param) {
var name = param.firstname;
var max = param.maxlength;
return name.length > max;
});
jQuery.validator.unobtrusive.adapters.add("fullnamemaxlength", ["firstname", "maxlength"], function (options) {
options.rules.fullnamemaxlength = {};
options.rules.fullnamemaxlength.firstname = options.params.firstname;
options.rules.fullnamemaxlength.maxlength = options.params.maximum;
options.messages.fullnamemaxlength = options.message;
}
);
}
Note this sits OUTSIDE of document.ready() { };
Something similar here: client-side validation in custom validation attribute - asp.net mvc 4