ASP.NET MVC Edit当选中dropdownlist中的对应项_ASP.NET

ASP.NET MVC Edit中选中dropdownlist中的对应项
Edit中Province可以对应到model中的对应省份，但是City就不行了，不知道怎么回事，基本一样的代码，不知道问题出哪里，求解。

C# code

    [Table("city")]    public class city    {        [Key]        [ScaffoldColumn(false)]        public string cityID { get; set; }        public string cityname { get; set; }        public string provinceid { get; set; }    }

C# code

    [Table("province")]    public class province    {        [Key]        public string provinceID { get; set; }        public string provinceName { get; set; }        public List<city> citys { get; set; }    }

C# code

    [Table("CompanyInfo")]    public class CompanyInfo    {        [Key]        public int id { get; set; }        [Required(AllowEmptyStrings=false, ErrorMessage="请输入单位名称")]        public string CompanyName { get; set; }        [Required(AllowEmptyStrings=false, ErrorMessage="请选择省份")]        public string ProvinceId { get; set; }        [Required(AllowEmptyStrings = false, ErrorMessage = "请选择城市")]        public string CityId { get; set; }        public List<AccountInfo> AccountInfos { get; set; }        public List<DepartmentId> DepartmentIds { get; set; }    }

C# code

    public class CRMEntities : DbContext    {        public DbSet<View_Company_List> View_Company_Lists { get; set; }        public DbSet<CompanyInfo> CompanyInfos { get; set; }        public DbSet<AccountInfo> AccountInfos { get; set; }        public DbSet<DepartmentId> DepartMentIds { get; set; }        public DbSet<province> provinces { get; set; }        public DbSet<city> citys { get; set; }    }

CompanyController.cs中

C# code

 //        // GET:  /Company/Edit/9        public ActionResult Edit(int id)        {            var companyInfo = CRMDB.CompanyInfos.Find(id);            ViewBag.ProvinceInf = new SelectList(CRMDB.provinces, "provinceID", "provinceName",companyInfo.ProvinceId);            ViewBag.CityInf = new SelectList(CRMDB.citys.Where(x => x.provinceid == companyInfo.ProvinceId), "cityID", "cityname", companyInfo.CityId);            return View(companyInfo);        }        //        // POST: /Company/Edit/        [HttpPost]        public ActionResult Edit(CompanyInfo companyInfo)        {            if (ModelState.IsValid)            {                CRMDB.Entry(companyInfo).State = EntityState.Modified;                CRMDB.SaveChanges();                return RedirectToAction("Index");            }            ViewBag.ProvinceInf = new SelectList(CRMDB.provinces, "provinceID", "provinceName", companyInfo.ProvinceId);            ViewBag.CityInf = new SelectList(CRMDB.citys.Where(x => x.provinceid == companyInfo.ProvinceId), "cityID", "cityname", companyInfo.CityId);            return View(companyInfo);        }

Edit.cshtml中

HTML code

@using (Html.BeginForm()) {    @Html.ValidationSummary(true)    <fieldset>        <legend>修改单位信息</legend>        @Html.HiddenFor(model => model.id)        <div class="editor-label">            @Html.LabelFor(model => model.CompanyName)        </div>        <div class="editor-field">            @Html.EditorFor(model => model.CompanyName)            @Html.ValidationMessageFor(model => model.CompanyName)        </div>        <div class="editor-label">            @Html.LabelFor(model => model.ProvinceId)        </div>        <div class="editor-field">            @Html.DropDownList("provinceID", (IEnumerable<SelectListItem>)ViewBag.ProvinceInf, "--请选择--", new { @style = "Width:100px" })            @Html.ValidationMessageFor(model => model.ProvinceId,"请选择省份")        </div>        <div class="editor-label">            @Html.LabelFor(model => model.CityId)        </div>        <div class="editor-field">            @Html.DropDownList("cityID", (IEnumerable<SelectListItem>)ViewBag.CityInf,"--请选择--", new { @style = "Width:100px" })            @Html.ValidationMessageFor(model => model.CityId,"请选择城市")        </div>        <p>            <input type="submit" value="Save" />        </p>    </fieldset>}