列表的自定义ValidationAttribute不会停止提交表单

Question

我尝试对列表进行客户端验证。我希望列表中至少有一个项目。

我使用此处找到的解决方案： ViewModel validation for a List

正在调用ValidationAttribute，当列表为空或为null时它返回false，但表单仍在提交。

型号：

public class ProductsViewModel
{
    UniformRepository repo;

    public ProductsViewModel()
    {
        repo = new UniformRepository();

        Products = new List<Product>();
        ProductToEdit = new Product();
        Divisions = repo.GetAllDivisions();
    }

    public List<Product> Products { get; set; }
    public Product ProductToEdit { get; set; }
    public Division SelectedDivision { get; set; }
    public List<SelectListItem> DropDownVendors { get; set; }

    public List<Division> Divisions { get; set; }

    [EnsureOneElement(ErrorMessage = "At least one vendor is required")]
    public List<string> Vendors { get; set; }
}

有问题的观点的一部分：

 <div class="row top-buffer">
        <div class="col-md-3 col-md-offset-1">
            @Html.LabelFor(model => model.Vendors, new { @class = "GridLabel" })
        </div>
        <div class="col-md-3">
            @(Html.Kendo().MultiSelectFor(model => model.Vendors)
                .BindTo(Model.DropDownVendors)
                .HtmlAttributes(new { @class = "form-control" }))
            @Html.ValidationMessageFor(model => model.Vendors, "", new { @class = "text-danger" })
        </div>
    </div>

ValidationAttribute

    public class EnsureOneElementAttribute : ValidationAttribute
    {
        public override bool IsValid(object value)
        {
            var list = value as IList;
            if (list != null)
            {
                return list.Count > 0;
            }
            return false;
        }
    }

感谢任何想法。