C# MVC中绑定数据到dropdownlist的问题

在学习MVC的过程中，在过去的两天里，试图将数据库中的数据绑定到MVC中的dropdownlist时遇到了很大的困难。我目前正在学习nerddinner教程。我一直严格遵循它，但不知何故还是以这个错误告终

具有该键的ViewData项 “晚餐。乡村”是一种 “System.String”，但必须是类型 “IEnumerable”

我知道这有很多代码要看，但如果有人想看一看，我会非常感激

这是我的密码：

ViewModel.cs

 public class DinnerFormViewModel
    {
        private static string[] _countries = new[] {
            "USA",
            "UK",
            "IRL",
            "SA"
        };

        //Properties
        public Dinner Dinner { get; private set; }
        public SelectList Countries { get; private set; }

        //Constructor
        public DinnerFormViewModel(Dinner dinner)
        {
            Dinner = dinner;

            Countries = new SelectList(_countries, dinner.Country);
        }

//
        //GET: /Dinners/Edit/2

        //[Authorize]
        public ActionResult Edit(int id)
        {
            Dinner dinner = dinnerrepository.GetDinner(id);

            //var countries = new[] {
              //  "USA", "Afganistan", "UK", "Ireland"};

            //ViewData["countries"] = new SelectList(countries, dinner.Country);

            return View(new DinnerFormViewModel(dinner));
        }

        //
        //POST: /Dinners/Edit/2

        [HttpPost]
        public ActionResult Edit(int id, FormCollection formvalues)
        {
            //Retrieve Existing Dinner
            Dinner dinner = dinnerrepository.GetDinner(id);

            //Update dinner with form posted values
            //dinner.Title = Request.Form["Title"];
            //dinner.Description = Request.Form["Description"];
            //dinner.EventDate = DateTime.Parse(Request.Form["EventDate"]);
            //dinner.Address = Request.Form["Address"];
            //dinner.Country = Request.Form["Country"];
            //dinner.ContactPhone = Request.Form["ContactPhone"];

            if (TryUpdateModel(dinner))
            {
                //Persist changes back to database
                dinnerrepository.Save();
                //Perform HTTP redirect to details page for the saved dinner
                return RedirectToAction("Details", new { id = dinner.DinnerID });
            }

            //var countries = new[] {
              //  "USA", "Afganistan", "UK", "Ireland"};

            //ViewData["countries"] = new SelectList(countries, dinner.Country);

            return View(new DinnerFormViewModel(dinner));
        }

dinerscontroller.cs

 public class DinnerFormViewModel
    {
        private static string[] _countries = new[] {
            "USA",
            "UK",
            "IRL",
            "SA"
        };

        //Properties
        public Dinner Dinner { get; private set; }
        public SelectList Countries { get; private set; }

        //Constructor
        public DinnerFormViewModel(Dinner dinner)
        {
            Dinner = dinner;

            Countries = new SelectList(_countries, dinner.Country);
        }

//
        //GET: /Dinners/Edit/2

        //[Authorize]
        public ActionResult Edit(int id)
        {
            Dinner dinner = dinnerrepository.GetDinner(id);

            //var countries = new[] {
              //  "USA", "Afganistan", "UK", "Ireland"};

            //ViewData["countries"] = new SelectList(countries, dinner.Country);

            return View(new DinnerFormViewModel(dinner));
        }

        //
        //POST: /Dinners/Edit/2

        [HttpPost]
        public ActionResult Edit(int id, FormCollection formvalues)
        {
            //Retrieve Existing Dinner
            Dinner dinner = dinnerrepository.GetDinner(id);

            //Update dinner with form posted values
            //dinner.Title = Request.Form["Title"];
            //dinner.Description = Request.Form["Description"];
            //dinner.EventDate = DateTime.Parse(Request.Form["EventDate"]);
            //dinner.Address = Request.Form["Address"];
            //dinner.Country = Request.Form["Country"];
            //dinner.ContactPhone = Request.Form["ContactPhone"];

            if (TryUpdateModel(dinner))
            {
                //Persist changes back to database
                dinnerrepository.Save();
                //Perform HTTP redirect to details page for the saved dinner
                return RedirectToAction("Details", new { id = dinner.DinnerID });
            }

            //var countries = new[] {
              //  "USA", "Afganistan", "UK", "Ireland"};

            //ViewData["countries"] = new SelectList(countries, dinner.Country);

            return View(new DinnerFormViewModel(dinner));
        }

下面是视图中给我带来问题的片段-Edit.aspx

<div class="editor-field">
                <%: Html.DropDownListFor(m => m.Dinner.Country, ViewData["countries"] as SelectList)%>
                <%: Html.ValidationMessageFor(m => m.Dinner.Country, "*")%>
            </div>

m、 晚餐。国家，查看数据[“国家”]作为选择列表）%>
m、 晚餐。国家，“*””>

此外，我还注释了一些代码，它们来自于本教程前面的内容，可以忽略。此外，对于任何能够真正理解堆栈跟踪的人来说，这里是：

InvalidOperationException: The ViewData item that has the key 'Dinner.Country' is of type 'System.String' but must be of type 'IEnumerable<SelectListItem>'.]
   System.Web.Mvc.Html.SelectExtensions.GetSelectData(HtmlHelper htmlHelper, String name) +458
   System.Web.Mvc.Html.SelectExtensions.SelectInternal(HtmlHelper htmlHelper, String optionLabel, String name, IEnumerable`1 selectList, Boolean allowMultiple, IDictionary`2 htmlAttributes) +321
   System.Web.Mvc.Html.SelectExtensions.DropDownListHelper(HtmlHelper htmlHelper, String expression, IEnumerable`1 selectList, String optionLabel, IDictionary`2 htmlAttributes) +48
   System.Web.Mvc.Html.SelectExtensions.DropDownListFor(HtmlHelper`1 htmlHelper, Expression`1 expression, IEnumerable`1 selectList, String optionLabel, IDictionary`2 htmlAttributes) +115
   System.Web.Mvc.Html.SelectExtensions.DropDownListFor(HtmlHelper`1 htmlHelper, Expression`1 expression, IEnumerable`1 selectList) +87
   ASP.views_dinners_edit_aspx.__RenderContent2(HtmlTextWriter __w, Control parameterContainer) in c:\Users\TaraW\Documents\Visual Studio 2010\Projects\NerdDinner\NerdDinner\Views\Dinners\Edit.aspx:52
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +109
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   ASP.views_shared_site_master.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in c:\Users\TaraW\Documents\Visual Studio 2010\Projects\NerdDinner\NerdDinner\Views\Shared\Site.Master:26
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +109
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Control.Render(HtmlTextWriter writer) +10
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +208
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +8
   System.Web.UI.Page.Render(HtmlTextWriter writer) +29
   System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer) +56
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +27
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3060

InvalidOperationException:具有键“Dinner.Country”的ViewData项的类型为“System.String”，但必须为“IEnumerable”类型。]
System.Web.Mvc.Html.SelectExtensions.GetSelectData（HtmlHelper HtmlHelper，字符串名）+458
System.Web.Mvc.Html.SelectExtensions.SelectInternal（HtmlHelper HtmlHelper，字符串选项标签，字符串名称，IEnumerable`1选择列表，布尔allowMultiple，IDictionary`2 htmlAttributes）+321
System.Web.Mvc.Html.SelectExtensions.dropdownlessAlper（HtmlHelper HtmlHelper，字符串表达式，IEnumerable`1选择列表，字符串选项标签，IDictionary`2 htmlAttributes）+48
System.Web.Mvc.Html.SelectExtensions.DropDownListFor（HtmlHelper`1 HtmlHelper，Expression`1 Expression，IEnumerable`1 selectList，String optionLabel，IDictionary`2 htmlAttributes）+115
System.Web.Mvc.Html.SelectExtensions.DropDownListFor（HtmlHelper`1 HtmlHelper，Expression`1 Expression，IEnumerable`1 selectList）+87
ASP.views\U dinners\U edit\U aspx.\U RenderContent2（HtmlTextWriter\UW，控制参数容器）在c:\Users\TaraW\Documents\Visual Studio 2010\Projects\NerdDinner\NerdDinner\views\diners\edit.aspx:52中
System.Web.UI.Control.RenderChildrenInternal（HtmlTextWriter编写器，ICollection子对象）+109
System.Web.UI.Control.RenderChildren（HtmlTextWriter）+8
System.Web.UI.Control.Render（HtmlTextWriter）+10
System.Web.UI.Control.RenderControlInternal（HtmlTextWriter编写器、ControlAdapter）+27
System.Web.UI.Control.RenderControl（HtmlTextWriter编写器、控制适配器）+100
System.Web.UI.Control.RenderControl（HtmlTextWriter）+25
ASP.views\u shared\u site\u master.\uuuu Render\uuuu control1（HtmlTextWriter\uuuuw，Control parameterContainer）在c:\Users\TaraW\Documents\Visual Studio 2010\Projects\NerdDinner\NerdDinner\views\shared\site中。master:26
System.Web.UI.Control.RenderChildrenInternal（HtmlTextWriter编写器，ICollection子对象）+109
System.Web.UI.Control.RenderChildren（HtmlTextWriter）+8
System.Web.UI.Control.Render（HtmlTextWriter）+10
System.Web.UI.Control.RenderControlInternal（HtmlTextWriter编写器、ControlAdapter）+27
System.Web.UI.Control.RenderControl（HtmlTextWriter编写器、控制适配器）+100
System.Web.UI.Control.RenderControl（HtmlTextWriter）+25
System.Web.UI.Control.RenderChildrenInternal（HtmlTextWriter编写器，ICollection子对象）+208
System.Web.UI.Control.RenderChildren（HtmlTextWriter）+8
System.Web.UI.Page.Render（HtmlTextWriter）+29
System.Web.Mvc.ViewPage.Render（HtmlTextWriter）+56
System.Web.UI.Control.RenderControlInternal（HtmlTextWriter编写器、ControlAdapter）+27
System.Web.UI.Control.RenderControl（HtmlTextWriter编写器、控制适配器）+100
System.Web.UI.Control.RenderControl（HtmlTextWriter）+25
System.Web.UI.Page.ProcessRequestMain（布尔includeStagesBeforeAsyncPoint，布尔includeStagesAfterAsyncPoint）+3060

更改此选项：

<%: Html.DropDownListFor(m => m.Dinner.Country, ViewData["countries"] as SelectList)%>

m.Dinner.Country，查看数据[“国家”]作为选择列表）%>

致：

m.Dinner.Country，Model.Countries.Items）%%>

首先，您需要定义一个属性，该属性将在视图模型上保存选定的国家/地区id：

public class DinnerFormViewModel
{
    private static string[] _countries = new[] {
        "USA",
        "UK",
        "IRL",
        "SA"
    };

    //Properties
    public Dinner Dinner { get; private set; }

    // will hold the selected country value
    public string SelectedCountry { get; set; }
    public SelectList Countries { get; private set; }

    //Constructor
    public DinnerFormViewModel(Dinner dinner)
    {
        Dinner = dinner;
        Countries = new SelectList(_countries, dinner.Country);
    }
}

然后：

<%: Html.DropDownListFor(m => m.SelectedCountry, Model.Countries) %>

m.SelectedCountry，Model.Countries）%%>

谢谢你的回复，但运气不好。