How to handle Booleans/CheckBoxes in ASP.NET MVC 2 with DataAnnotations?

Question

I\'ve got a view model like this:

public class SignUpViewModel
{
    [Required(ErrorMessage = \"Bitte lesen und akzeptieren Sie die AGB.\")]
    [DisplayName         


        

Answer 1

Found a more complete solution here (both server and client side validation):

http://blog.degree.no/2012/03/validation-of-required-checkbox-in-asp-net-mvc/#comments

Answer 2

My Solution is as follows (it's not much different to the answers already submitted, but I believe it's named better):

/// <summary>
/// Validation attribute that demands that a boolean value must be true.
/// </summary>
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
public class MustBeTrueAttribute : ValidationAttribute
{
    public override bool IsValid(object value)
    {
        return value != null && value is bool && (bool)value;
    }
}

Then you can use it like this in your model:

[MustBeTrue(ErrorMessage = "You must accept the terms and conditions")]
[DisplayName("Accept terms and conditions")]
public bool AcceptsTerms { get; set; }

Answer 3

The proper way to do this is to check the type!

[Range(typeof(bool), "true", "true", ErrorMessage = "You must or else!")]
public bool AgreesWithTerms { get; set; }

Answer 4

This might be a "hack" but you can use the built in Range attribute:

[Display(Name = "Accepted Terms Of Service")]
[Range(typeof(bool), "true", "true")]
public bool Terms { get; set; }

The only problem is the "warning" string will say "The FIELDNAME must be between True and true".

Answer 5

It's enough to add [RegularExpression]:

[DisplayName("I accept terms and conditions")]
[RegularExpression("True", ErrorMessage = "You must accept the terms and conditions")]
public bool AgreesWithTerms { get; set; }

Note - "True" must start with capital T

Answer 6

I'm just taking the best of the existing solutions and putting it together into a single answer that allows for both server side and client side validation.

The to apply to model a properties to ensure a bool value must be true:

/// <summary>
/// Validation attribute that demands that a <see cref="bool"/> value must be true.
/// </summary>
/// <remarks>Thank you <c>http://stackoverflow.com/a/22511718</c></remarks>
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
public class MustBeTrueAttribute : ValidationAttribute, IClientValidatable
{
    /// <summary>
    /// Initializes a new instance of the <see cref="MustBeTrueAttribute" /> class.
    /// </summary>
    public MustBeTrueAttribute()
        : base(() => "The field {0} must be checked.")
    {
    }

    /// <summary>
    /// Checks to see if the given object in <paramref name="value"/> is <c>true</c>.
    /// </summary>
    /// <param name="value">The value to check.</param>
    /// <returns><c>true</c> if the object is a <see cref="bool"/> and <c>true</c>; otherwise <c>false</c>.</returns>
    public override bool IsValid(object value)
    {
        return (value as bool?).GetValueOrDefault();
    }

    /// <summary>
    /// Returns client validation rules for <see cref="bool"/> values that must be true.
    /// </summary>
    /// <param name="metadata">The model metadata.</param>
    /// <param name="context">The controller context.</param>
    /// <returns>The client validation rules for this validator.</returns>
    public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
    {
        if (metadata == null)
            throw new ArgumentNullException("metadata");
        if (context == null)
            throw new ArgumentNullException("context");

        yield return new ModelClientValidationRule
            {
                ErrorMessage = FormatErrorMessage(metadata.DisplayName),
                ValidationType = "mustbetrue",
            };
    }
}

The JavaScript to include to make use of unobtrusive validation.

jQuery.validator.addMethod("mustbetrue", function (value, element) {
    return element.checked;
});
jQuery.validator.unobtrusive.adapters.addBool("mustbetrue");