ASP.NET M5C实现下拉框多选

我们知道，在ASP.NET MVC中实现多选Select的话，使用Html.ListBoxFor或Html.ListBox方法就可以。在实际应用中，到底该如何设计View Model， 控制器如何接收多选Select的选中项呢？

实现效果如下：

初始状态某些选项被选中。

当按着ctrl键，进行重新选择多项，点击"提交"按钮，把选中项的id拼接。

对于Select中的项，包含显示值，Value值，以及是否选中，抽象成如下的类。

public class City{public int Id { get; set; }public string Name { get; set; }public bool IsSelected { get; set; }}

对于整个多选Select来说，在ASP.NET MVC中，所有的选项被看作SelectListItem类型，选中的项是一个string类型的集合。于是多选Select的View Model设计为：

public class CityVm{public IEnumerable<SelectListItem>Cities { get; set; }public IEnumerable<string> SelectedCities { get; set; }}

在HomeController中，把SelectListItem的集合赋值给CityVm的Cities属性。

public class HomeController : Controller{public ActionResult Index(){var cities = new List<City>{new City(){Id = 1, Name = "青岛", IsSelected = true},new City(){Id = 2, Name = "胶南", IsSelected = false},new City(){Id = 3, Name = "即墨", IsSelected = true},new City(){Id = 4, Name = "黄岛", IsSelected = false},new City(){Id = 5, Name = "济南", IsSelected = false}};var citiesToPass = from c in citiesselect new SelectListItem() {Text = c.Name, Value = c.Id.ToString(),Selected = c.IsSelected};CityVm cityVm = new CityVm();cityVm.Cities = citiesToPass;ViewData["cc"] = citiesToPass.Count();return View(cityVm);}......}

在Home/Index.cshtml中,是一个CityVm的强类型视图，对于选中的项会以IEnumerable<string>集合传递给控制器。

@model MvcApplication1.Models.CityVm@{ViewBag.Title = "Index";Layout = "~/Views/Shared/_Layout.cshtml";}<h2>Index</h2>@using (Html.BeginForm("GetCities", "Home", FormMethod.Post, new {id = "myForm"})){ @Html.ListBoxFor(c => c.SelectedCities, Model.Cities, new {size = ViewData["cc"]})<br/><input type="submit" value="提交"/>}

在HomeController中，再把从视图传递过来的IEnumerable<string>拼接并呈现。

public class HomeController : Controller{......[HttpPost]public ActionResult GetCities(IEnumerable<string> selectedCities){if (selectedCities == null){return Content("没有选中任何选项");}else{StringBuilder sb = new StringBuilder();sb.Append("选中项的Id是：" + string.Join(",", selectedCities));return Content(sb.ToString());}}}