.net MVC 下拉多级联动及MVC Html.DropDownList 和DropDownListFor

第一种方式

前台html

    省份：
    
        请选择
    

    市：
    
        请选择
    

jquery

后台代码

/// 

        /// 模拟省份数据
        /// 
        /// 
        public List Provincelist()
        {
            List list = new List();
            list.Add(new Province() { PID = 1, ProvinceName = "广东" });
            list.Add(new Province() { PID = 2, ProvinceName = "北京" });
            list.Add(new Province() { PID = 3, ProvinceName = "上海" });
            list.Add(new Province() { PID = 4, ProvinceName = "河北" });
            list.Add(new Province() { PID = 5, ProvinceName = "贵州" });
            list.Add(new Province() { PID = 6, ProvinceName = "云南" });

            return list;
        }

        /// 

        /// 模拟城市数据
        /// 
        /// 
        public List Citylist()
        {
            List cityList = new List();
            cityList.Add(new City() { CID = 1, PID = 1, CityName = "广州" });
            cityList.Add(new City() { CID = 2, PID = 1, CityName = "深圳" });
            cityList.Add(new City() { CID = 3, PID = 1, CityName = "惠州" });
            cityList.Add(new City() { CID = 4, PID = 1, CityName = "湛江" });
            cityList.Add(new City() { CID = 5, PID = 2, CityName = "北京" });
            cityList.Add(new City() { CID = 6, PID = 3, CityName = "上海" });
            cityList.Add(new City() { CID = 7, PID = 4, CityName = "唐山市" });
            cityList.Add(new City() { CID = 8, PID = 4, CityName = "保定市" });
            cityList.Add(new City() { CID = 9, PID = 4, CityName = "张家口市" });
            return cityList;
        }


        /// 

        /// 获取省份
        /// 
        public JsonResult GetProvincelist()
        {
            var list = Provincelist();
            return Json(list, JsonRequestBehavior.AllowGet);
        }

        /// 

        /// 获取城市
        /// 
        /// 
        /// 
        [WithoutLocalization]
        public JsonResult GetCitylist(int pid)
        {
            var citys = Citylist().Where(m => m.PID == pid).ToList();

            List item = new List();

            foreach (var City in citys)
            {
                item.Add(new SelectListItem { Text = City.CityName, Value = City.CID.ToString() });
            }
            return Json(item, JsonRequestBehavior.AllowGet);
        }

第二种方式

前台html

model需要在该页面首行添加类的引用，@model WebApplicationShare.Controllers.ProvinceViewModel

    省份：
    @Html.DropDownListFor(model => model.PID,ViewBag.ProvinceList as IEnumerable, "＝请选择＝", new { @class = "form-control", id = "Province" })


    市：
    @Html.DropDownListFor(model => model.CID, ViewBag.CityList as IEnumerable, "＝请选择＝", new { @class = "form-control", id = "City" })

jquery代码（和上面的那个几乎一样，区别在于初始化的时候不加载省份，而是加载城市）

$(function () {
        //GetProvince(); //加载省份
        GetCity();
        $("#Province").change(function () {
            GetCity();
        });
    });
    function GetProvince() {
        //        $("#Province").empty();
        $.getJSON(
            "/Home/GetProvincelist",
            function (data) {

                $.each(data, function (i, item) {
                    $("").val(item["PID"]).text(item["ProvinceName"]).appendTo($("#Province"));
                })
            });
        //            GetCity();
    }
    function GetCity() {
        $("#City").empty();
        $.getJSON(
        "/Home/GetCitylist",
        { pid: $("#Province").val() } ,
        function (data) {
            $.each(data, function (i, item) {
                $("").val(item["Value"]).text(item["Text"]).appendTo($("#City"));

            })
        });
    }

 后台代码

public ActionResult Index()
        {
            ViewBag.ProvinceList = Provincelist().Select(m => new SelectListItem()
            {
                Text = m.ProvinceName,
                Value = m.PID.ToString(),
                Selected = (m.PID == 4) //测试，默认让它绑定第四个
            }).ToList();
            ViewBag.CityList = Citylist().Select(m => new SelectListItem()
            {
                Text = m.CityName,
                Value = m.CID.ToString(),
                Selected = (m.CID == 9) //测试发现这个设置了没啥用
            }).ToList();
            return View();
        }
public class ProvinceViewModel
    {
        /// 

        /// 省份ID
        /// 
        public int PID { get; set; }

        /// 

        /// 城市ID
        /// 
        public int CID { get; set; }
    }

参考网址：https://www.cnblogs.com/jys509/p/4554688.html#autoid-0-0-0

不理解原博主说的编辑是什么意思，我自己试了之后只能实现级联，而且还有一些小bug，比如省份如果选择请选择，城市那边获取不到省份的pid导致F12输出中报错

DropDownList用法

后台代码

public SelectList CardTypeSelectList(int? value)
            {
            List dic_dtList = CardTypeService.LoadEntities(c => c.VALID == 1).ToList();
            dic_dtList.Insert(0, new dic_docmenttype { CODE = 0, DVALUE = "请选择" });
            return new SelectList(dic_dtList, "CODE", "DVALUE", value);
        }

    public ActionResult Index()
        {
          
            int CardValue = 0;
            ViewData["RY_cardType"] = CardTypeSelectList(CardValue);
            return View();
        }

前台html

                        * 证件类型
                        

                            @Html.DropDownList("RY_cardType", null, new { @class = "form-control allCardType" })
                        
                    

参考网址：https://blog.csdn.net/pt_sm/article/details/53893899

这个博客写的挺详细的