@ html.DropDownList对于选定值未发布到发布操作

Question

public class RegionUpdateDbViewModel
    {
        [Required]
        public string RegionName { get; set; }        
        public int RegionLevel { get; set; }
        public Guid ParentRegionId { get; set; }        
        public bool IsDeleted { get; set; } = false;
        //public List<Guid> CountryIDList { get; set; }
        public List<CountryViewModel> CountryIDList { get; set; }
        public Guid? UserModifiedById { get; set; }
        public Guid? UserDeletedById { get; set; }
        public DateTime? ModifiedOn { get; set; }
        public DateTime? DeletedOn { get; set; }
        [Required]
        public Guid Id { get; set; }
    }

RegionUpdateDbViewModel是区域更新的模型。在Edit.cshtm中，我有一个用于国家列表的下拉列表。

@Html.DropDownListFor(Model => Model.CountryIDList, (SelectList)(ViewBag.selectedCountryList), "Please select", new { @class = "form-control", multiple = "multiple" })

发布时，我还没有从dropswnlist中选择特定的国家。 以下是我的帖子操作。

[HttpPost]
        public IActionResult Edit(RegionUpdateDbViewModel region)
        {
            try
            {
                var contollerName = this.ControllerContext.RouteData.Values["controller"].ToString();
                HttpResponseMessage response = _serviceRepository.PutResponse(contollerName, region);
                response.EnsureSuccessStatusCode();
            }
            catch (Exception ex)
            {
            }
            return RedirectToAction("Index");
        }