public ActionResult AddDistrict(District model)
 {
     var cities = db.Cities.OrderBy(c => c.CityName).ToList();
     ViewBag.Cities = cities;
     if (ModelState.IsValid)
     {
         var district = new District();
         district.DistrictName = model.DistrictName;
         district.CityID = model.CityID;
         db.Districts.Add(district);
         db.SaveChanges();
         return Redirect("/Admin/Foundation/District");
     }
     else
     {
         ModelState.AddModelError("", "区县信息失败");
     }
     return View();
 }
        public ActionResult DistrictEdit(District model)
        {
            var district = db.Districts.Find(model.ID);
            List<SelectListItem> cityList = new List<SelectListItem>();
            var cities = db.Cities.ToList();
            foreach (var city in cities)
            {
                cityList.Add(new SelectListItem { Text = city.CityName, Value = city.ID.ToString(), Selected = (city.ID == district.CityID ? true : false) });
            }
            ViewBag.CityList = cityList;
            ViewBag.District = district;

            if (ModelState.IsValid)
            {
                district.DistrictName = model.DistrictName;
                district.CityID = model.CityID;
                db.SaveChanges();
                return Redirect("/Admin/Foundation/District");
            }
            else
            {
                ModelState.AddModelError("", "区县信息失败");
            }
            return View();
        }