MVC实现多选下拉框

借助Chosen Plugin可以实现多选下拉框。

选择多项：

设置选项数量，比如设置最多允许2个选项：

考虑到多选下拉<select multiple="multiple"...></select>选中项是string数组，Model应该这样设计：

using System.Collections.Generic;
using System.Web.Mvc;

namespace MvcApplication1.Models
{
    public class CarVm
    {
        public string[] SelectedCars { get; set; }
        public IEnumerable<SelectListItem>  AllCars { get; set; }
    }
}

HomeController中：

using System.Collections.Generic;
using System.Linq;
using System.Web.Mvc;
using MvcApplication1.Models;

namespace MvcApplication1.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            CarVm carVm = new CarVm();
            carVm.SelectedCars = new string[]{"1","2"};
            carVm.AllCars = GetAllCars();
            return View(carVm);
        }

        [HttpPost]
        public ActionResult SaveCars(CarVm carVm)
        {
            if (ModelState.IsValid)
            {
                return View(carVm);
            }
            return RedirectToAction("Index", carVm);
        }

        private IEnumerable<SelectListItem> GetAllCars()
        {
            List<SelectListItem> allCars = new List<SelectListItem>();
            allCars.Add(new SelectListItem() {Value = "1",Text = "奔驰"});
            allCars.Add(new SelectListItem() { Value = "2", Text = "宝马" });
            allCars.Add(new SelectListItem() { Value = "3", Text = "奇瑞" });
            allCars.Add(new SelectListItem() { Value = "4", Text = "比亚迪" });
            allCars.Add(new SelectListItem() { Value = "5", Text = "起亚" });
            allCars.Add(new SelectListItem() { Value = "6", Text = "大众" });
            allCars.Add(new SelectListItem() { Value = "7", Text = "斯柯达" });
            allCars.Add(new SelectListItem() { Value = "8", Text = "丰田" });
            allCars.Add(new SelectListItem() { Value = "9", Text = "本田" });

            return allCars.AsEnumerable();
        }
    }
}

Home/Index.cshtml视图中，需要引用Chosen Plugin的css和js文件：

@model MvcApplication1.Models.CarVm

@{
    ViewBag.Title = "Index";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Index</h2>
<link href="~/Content/chosen.css" rel="stylesheet" />

@using (Html.BeginForm("SaveCars", "Home", FormMethod.Post))
{
    @Html.LabelFor(m => m.SelectedCars,"最多选择2个选项") <br/>
    @Html.ListBoxFor(m => m.SelectedCars, Model.AllCars, new {@class="chosen", multiple="multiple", style="width:350px;"}) <br/>
    <input type="submit" value="提交"/>
}

@section scripts
{
    <script src="~/Scripts/chosen.jquery.min.js"></script>
    <script type="text/javascript">
        $(function() {
            $('.chosen').chosen({
                max_selected_options: 2
            });

            $(".chosen-deselect").chosen(
            {
                allow_single_deselect: true
            });

            $(".chosen").chosen().change();
            $(".chosen").trigger('liszt:updated');
        });
    </script>
}