HowTo: change color of validation messages in ASP.net MVC

If you need to customize the colors (or do more restyling) of validation messages in ASP.net MVC, the following snippet from a discussion on ASP.net forums should be useful:

Add to Content/Site.css:

/* styles for validation helpers */

.field-validation-error {
    color: #b94a48;
}

.field-validation-valid {
    display: none;
}

input.input-validation-error {
    border: 1px solid #b94a48;
}

select.input-validation-error {
    border: 1px solid #b94a48;
}

input[type="checkbox"].input-validation-error {
    border: 0 none;
}

.validation-summary-errors {
    color: #b94a48;
}

.validation-summary-valid {
    display: none;
}

Other useful replies from there:

@Html.ValidationSummary(true,"",new {@style= "color: red"})

The method for MVC 5 + Bootstrap is:
@Html.ValidationSummary(true, "", new { @class = "text-danger" })

HowTo: include MVC model property Display name in Required validation message

Just came across this validation error display in an MVC app I’ve recently started maintaining. The required input field validation seemed to not be localized, resulting in a mixed English and Greek (from the field’s Display name) message:

Looking at the MVC model I noticed they were using [Required] attributes for the userName and password properties, together with [Display(Name = "…")] for the displayed property title

public class LoginModel
  {
     [Required]
     [Display(Name = "Όνομα Χρήστη")]
     public string userName { get; set; }

     [Required]
     [DataType(DataType.Password)]
     [Display(Name = "Κωδικός")]
     public string password { get; set; }

     //…

That was changed to:

public class LoginModel
  {
     [Required(ErrorMessage = "Το {0} είναι απαραίτητο.")]
     [Display(Name = "Όνομα Χρήστη")]
     public string userName { get; set; }

     [Required(ErrorMessage = "Το {0} είναι απαραίτητο.")]
     [DataType(DataType.Password)]
     [Display(Name = "Κωδικός")]
     public string password { get; set; }

resulting in a fully localized validation error message with the respective property’s Display name auto-inserted in the validation ErrorMessage, thanks to the {0} used in the message string:

Note there’s also the lazy route like in this property:

[Display(Name = "Περίοδος Εγγύησης(Έτη):")]
[Required(ErrorMessage = "Απαραίτητο πεδίο")]
public int warrantyPeriod { get; set; }

where you just say something like “Required field” in the localized error message. This however will work only when you always show the error message next to the input field that fails to pass validation.

If you want to also show a validation summary say at the beginning and/or the end of the page (depending on where your submit button is), you’ll end up with an error summary that may just contain multiple entries of “Required field” text without any indication on what field it was (which would be practically useless that is).

Note that sometimes due to lack of space in a webpage (say if you have lots of input fields in a grid) you can only show say red “*” near input fields that have validation errors and explain them more in the tooltips and in an error summary control.

Even better you can use resource strings to avoid error message string duplication. That approach, though a bit more verbose as implemented in ASP.net means easier centralized maintenance and localization from a per locale/language resource file and less typos or slightly different error messages for the same thing. See example and related screenshots at https://stackoverflow.com/a/22849638

Validating E-mails using Regular Expressions in Java

To sum up the discussion at http://stackoverflow.com/questions/1360113/is-java-regex-thread-safe/, you can reuse (keep in static variables) the compiled Pattern(s) and tell them to give you new Matchers when needed to validate those regex pattens against some string:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Validation helpers
 */ 
public final class Validators {  

  private static final String EMAIL_PATTERN = 
    "^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*
     @[A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*(\\.[A-Za-z]{2,})$";
  
  private static Pattern email_pattern;  

  static {  
    email_pattern = Pattern.compile(EMAIL_PATTERN);
  }

  /**
   * Check if e-mail is valid 
   */   
  public static boolean isValidEmail(String email) {    
    Matcher matcher = email_pattern.matcher(email);
    return matcher.matches(); 
  }

}

(Note: the EMAIL_PATTERN string should be put in a single line)

For the RegEx pattern used, see the article at http://www.mkyong.com/regular-expressions/how-to-validate-email-address-with-regular-expression/ and the user comments (and useful links) posted there.

Update (20120715): previous pattern wasn’t accepting “-” in the domain name