ASP.NET MVC: Why Range Data Annotation is not working on checkbox in client side?

I finally came with this solution:

public class EnforceTrueAttribute : ValidationAttribute, IClientValidatable
    {
        public override bool IsValid(object value)
        {
            if (value == null) return false;
            if (value.GetType() != typeof(bool)) throw new InvalidOperationException("can only be used on boolean properties.");
            return (bool)value == true;
        }

        public override string FormatErrorMessage(string name)
        {
            return "The " + name + " field must be checked in order to continue.";
        }

        public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
        {
            yield return new ModelClientValidationRule
            {
                ErrorMessage = String.IsNullOrEmpty(ErrorMessage) ? FormatErrorMessage(metadata.DisplayName) : ErrorMessage,
                ValidationType = "enforcetrue"
            };
        }
    }

And in my JS:

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