Asp.net mvc 4 下拉列表MVC4错误

我正试图得到一个下拉列表工作，但它不适合我。此应用程序主要是基于节日的应用程序，您可以在活动中添加节日。我遇到的错误是在线的：

@Html.DropDownList("towns", (IEnumerable<SelectListItem>)ViewData["Town"], new{@class = "form-control", @style="width:250px" })

---

我怀疑当您将表单提交到

[HttpPost]

操作时，而不是在呈现表单时，会发生此错误，对吗？这个动作会呈现包含下拉列表的相同视图，对吗？在这个

[HttpPost]

操作中，您忘记了像在HttpGet操作中一样填充

ViewData[“Town”]

值，对吗

因此，继续并以与GET操作相同的方式填充此属性。当您向

[HttpPost]

操作提交表单时，仅将所选值发送给控制器。因此，如果要重新显示同一视图，则需要重新填充集合值，因为此视图呈现一个下拉列表，试图从

ViewData[“Town”]

绑定其值

以下是我对代码的理解：

[HttpPost]
public ActionResult SomeAction(Festival model)
{
    ... bla bla bla

    // don't forget to repopulate the ViewData["Town"] value the same way you did in your GET action
    // if you intend to redisplay the same view, otherwise the dropdown has no way of getting
    // its values
    ViewData["Town"] = ... same stuff as in your GET action

    return View(model);
}

---

尽管如此，我还是强烈建议您使用视图模型，而不是ViewData/ViewBag弱类型的东西。不仅您的代码将变得更加干净，甚至错误消息也将开始有意义。

啊，好的，我明白了，谢谢。在viewmodel中获取它容易吗？我才刚刚开始理解mvc，我试过了，现在我在代码背后的下拉列表中出现了一个错误。第195行：第195行：festival.FestivalTown.Name=fcFestival[“镇]；这有什么问题？

//Get
List<SelectListItem> Towns = new List<SelectListItem>();
Towns.Add(new SelectListItem { Text = "Please select your Town", Value = "SelectTown" });
var towns = (from t in db.Towns select t).ToArray();
for (int i = 0; i < towns.Length; i++)
{
Towns.Add(new SelectListItem
{
Text = towns[i].Name,
Value = towns[i].Name.ToString(),
Selected = (towns[i].ID == 0)
});
}

ViewData["Town"] = Towns;

//Post
festival.FestivalTown.Town = collection["Town"];

    public class Festival
{
    public int FestivalId { get; set; }

    [Required]
    [Display(Name = "Festival Name"), StringLength(100)]
    public string FestivalName { get; set; }

    [Required]
    [Display(Name = "Start Date"), DataType(DataType.Date)]
    public DateTime StartDate { get; set; }

    [Required]
    [Display(Name = "End Date"), DataType(DataType.Date)]
    public DateTime EndDate { get; set; }

    [Required]
    [Display(Name = "County")]
    public virtual County FestivalCounty { get; set; }

    [Display(Name = "Festival Location")]
    public DbGeography Location { get; set; }

    [Required]
    [Display(Name = "Town")]
    public virtual Town FestivalTown { get; set; }

    [Required]
    [Display(Name = "Festival Type")]
    public virtual FestivalType FType { get; set; }

    public UserProfile UserId { get; set; }
}

    public class Town
{
    public int ID { get; set; }
    [Display(Name = "Town")]
    public string Name { get; set; }
}

[HttpPost]
public ActionResult SomeAction(Festival model)
{
    ... bla bla bla

    // don't forget to repopulate the ViewData["Town"] value the same way you did in your GET action
    // if you intend to redisplay the same view, otherwise the dropdown has no way of getting
    // its values
    ViewData["Town"] = ... same stuff as in your GET action

    return View(model);
}