我們知道，在ASP.NET MVC中實(shí)現(xiàn)多選Select的話，使用Html.ListBoxFor或Html.ListBox方法就可以。在實(shí)際應(yīng)用中，到底該如何設(shè)計(jì)View Model， 控制器如何接收多選Select的選中項(xiàng)呢？

實(shí)現(xiàn)效果如下：

初始狀態(tài)某些選項(xiàng)被選中。

當(dāng)按著ctrl鍵，進(jìn)行重新選擇多項(xiàng)，點(diǎn)擊"提交"按鈕，把選中項(xiàng)的id拼接。

對(duì)于Select中的項(xiàng)，包含顯示值，Value值，以及是否選中，抽象成如下的類。

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

對(duì)于整個(gè)多選Select來(lái)說(shuō)，在ASP.NET MVC中，所有的選項(xiàng)被看作SelectListItem類型，選中的項(xiàng)是一個(gè)string類型的集合。于是多選Select的View Model設(shè)計(jì)為：

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

在HomeController中，把SelectListItem的集合賦值給CityVm的Cities屬性。

    public class HomeController : Controller    {public ActionResult Index(){    var cities = new List<City>    {new City(){Id = 1, Name = "青島", IsSelected = true},new City(){Id = 2, Name = "膠南", IsSelected = false},new City(){Id = 3, Name = "即墨", IsSelected = true},new City(){Id = 4, Name = "黃島", IsSelected = false},new City(){Id = 5, Name = "濟(jì)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,是一個(gè)CityVm的強(qiáng)類型視圖，對(duì)于選中的項(xiàng)會(huì)以IEnumerable<string>集合傳遞給控制器。

@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，再把從視圖傳遞過(guò)來(lái)的IEnumerable<string>拼接并呈現(xiàn)。

    public class HomeController : Controller    {......[HttpPost]public ActionResult GetCities(IEnumerable<string> selectedCities){    if (selectedCities == null)    {return Content("沒(méi)有選中任何選項(xiàng)");    }    else    {StringBuilder sb = new StringBuilder();sb.Append("選中項(xiàng)的Id是：" + string.Join(",", selectedCities));return Content(sb.ToString());    }}    }

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