ASP.NETMVC验证标注的扩展checkbox必选

public class BooleanRequiredAttribute : ValidationAttribute, IClientValidatable
    {
        public bool Value { get; set; }
        public override bool IsValid(object value) { res = value != null && Value; return res; }

        public IEnumerable GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
        {
            ModelClientValidationRule rule = new ModelClientValidationRule
            {
                ValidationType = "brequired",
                ErrorMessage = FormatErrorMessage(metadata.GetDisplayName())
            };
            rule.ValidationParameters.Add("br", res);
            yield return rule;
        }

        public bool res { get; set; }
    }

//布尔类型必勾选
$.validator.addMethod("brequired", function (value, element, param) {
    return element.checked;
});
$.validator.unobtrusive.adapters.addSingleVal("brequired", "br");

        [BooleanRequired]
        [Display(Name = "必选同意")]
        public bool Agree { get; set; }

"showclause" href="Javascript:void(0);">网站服务条款
                            @Html.CheckBoxFor(m => m.Agree)同意 
                            @Html.ValidationMessageFor(m => m.Agree)