具有键 'Survey_Group' 的 ViewData 项是 'System.String' 类型，但必须是 'IEnumerable<SelectListItem>' 类型

Question

我已经将数据库中的值绑定到下拉列表。但是当我尝试在视图中提交时，它显示：

The ViewData item that has the key 'Survey_Group' is of type 'System.String' but must be of type 'IEnumerable'.

谁能指导一下？谢谢。

型号：

[MaxLength(100)]
[DisplayName("Owner Groups")]
public string Survey_Group { get; set; }

查看：

@Html.LabelFor(model => model.Survey_Group, "Owner Groups")
@Html.DropDownListFor(model => model.Survey_Group, (SelectList)ViewBag.GroupList)

控制器：

public ActionResult SURV_Main_Create()
{
    ViewBag.CurrentPage = "create";
    var model = new SURV_Main_Model();
    ViewBag.GroupList = new SelectList(db.SURV_Group_Model, "Group_ID", "GroupName");
    return View(model);
}

// POST: /SURV_Main/Create
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult SURV_Main_Create(SURV_Main_Model surv_main_model)
{
    if (ModelState.IsValid)
    {
        var r = new Random();
        int randomno = r.Next(1, 1000000);
        surv_main_model.Survey_Key = "SURV" + DateTime.Now.ToString("yyyyMMddHHmmss") + randomno;
        surv_main_model.Survey_Creator = User.Identity.Name;
        db.SURV_Main_Model.Add(surv_main_model);
        db.SaveChanges();
        return RedirectToAction("SURV_Main_Edit", new { id = surv_main_model.Survey_ID });
    }
    return View(surv_main_model);
}

Answer 1

在您的 POST 方法中，当模型无效时，您 return 视图，但没有为 ViewBag.GroupList 赋值（您在 DropDownListFor() 方法）所以它是空的，因此是例外。

在你需要的POST方法中

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult SURV_Main_Create(SURV_Main_Model surv_main_model)
{
  if (ModelState.IsValid)
  {
    ....
  }
  ViewBag.GroupList = new SelectList(db.SURV_Group_Model, "Group_ID", "GroupName"); // add this
  return View(surv_main_model);
}

具有键 'Survey_Group' 的 ViewData 项是 'System.String' 类型，但必须是 'IEnumerable<SelectListItem>' 类型

The ViewData item that has the key 'Survey_Group' is of type 'System.String' but must be of type 'IEnumerable<SelectListItem>'

c#

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asp.net-mvc-4