没有“ViewData”类型的“IEnumerable<SelectListItem>”项具有“RouterElect”键

Question

这个问题以前曾被问过类似的问题，但我不知道如何将这些答案应用于我的具体问题：

ViewModel

   public string RouterElect { get; set; }

视图

    if ((!string.IsNullOrWhiteSpace(Model.JudgeCode)) && (Model.userIsAuthorized))
    {
        <div id="ChangeRouterSection" class="live-tile" data-mode="carousel" data-direction="vertical" data-delay="7000">
             @{Html.RenderPartial("_ChangeCurrentRouter");}
        </div>
    }
    else
    {
        <div id="ChangeRouterSection" class="live-tile" data-mode="carousel" data-direction="vertical" data-delay="7000">
            <div class="tile">
                User not authorized. Access denied.
            </div>
        </div>
    }

局部视图

    @model JudicialPortal.ViewModels.PortalIndexView

    <div class="tile">
        Change Current Router
        @Html.DropDownListFor(x => x.RouterElect, Model.JPortalChamberUsersAsItems, new { @id = "changeCurrentRouterInput", @class = "m-wrap", @onchange = "" })
        <button type="button" class="m-btn green-stripe" onclick="changeCurrentRouter();"
        style="color: #444; text-decoration: none;">
        Okay</button>
    </div>

当页面加载时，它将无问题地呈现，如下所示：

从呈现页中平铺

但是，当选择下拉列表中的项，然后单击OKay按钮时，会发生以下错误：

没有具有'RouterElect‘键的'IEnumerable’类型的IEnumerable项。

对于代码行：

@Html.DropDownListFor(x => x.RouterElect, Model.JPortalChamberUsersAsItems, new { @id = "changeCurrentRouterInput", @class = "m-wrap", @onchange = "" })

任何想法都很感激。

更新:有人询问JPortalChamberUsersAsItems后端代码：

    JPortalChamberUsersAsItems = new List<SelectListItem>();

    if (HttpContext.Current.Session["JPortalChamberUsersAsItems"] != null)
    {
        JPortalChamberUsersAsItems = HttpContext.Current.Session["JPortalChamberUsersAsItems"] as List<SelectListItem>;
    }
    else
    {
        for (int i = 0; i < tempArrayOfUsers.Count; i++)
        {
            JPortalChamberUsersAsItems.Add(new SelectListItem { Text = tempArrayOfUsers[i], Value = tempArrayOfUsers[i] });
        }

        foreach (SelectListItem routerUser in JPortalChamberUsersAsItems)
        {
            if (!string.IsNullOrWhiteSpace(routerUser.Text))
            {
                if (routerUser.Text.ToUpper() != "PLEASE SELECT A ROUTER")
                {
                    routerUser.Text = ReplaceUsernameWithFullName(routerUser.Text);
                }
            }
        }

        JPortalChamberUsersAsItems.Insert(0, (new SelectListItem { Text = "Please select a router", Value = "Please select a router" })); //2014-12-15 This code adds the "default" first option - DO NOT REMOVE

        HttpContext.Current.Session.Add("JPortalChamberUsersAsItems", JPortalChamberUsersAsItems);
    }

另一个问题是关于OKay的行动。它调用changeCurrentRouter脚本，该脚本执行ChangeCurrrentRouter操作：

public ActionResult ChangeCurrentRouter(string changeCurrentRouterInput, string JudgeCode, bool userIsAuthorized, PortalIndexView viewmodel)
{
    bool databaseCallOk = false;
    string errorString = "";
    viewmodel.userIsAuthorized = userIsAuthorized;
    viewmodel.JudgeCode = JudgeCode;

    if (!string.IsNullOrWhiteSpace(changeCurrentRouterInput))
    {
        if (changeCurrentRouterInput.ToUpper() != "PLEASE SELECT A ROUTER")
        {
            //database call
            databaseCallOk = viewmodel.changeRouterUser(changeCurrentRouterInput, JudgeCode);
        }
    }

    if (databaseCallOk == false)
    {
        if (string.IsNullOrWhiteSpace(viewmodel.errorCatcher))
        {

            errorString = "An error occurred trying to change the router for your chambers. Please confirm your selection and try again.";
            viewmodel.errorCatcher = errorString;
        }
    }

    viewmodel.justAttemptedRoutingChange = true;

    return PartialView("~/Views/Shared/_ChangeCurrentRouter.cshtml", viewmodel);
}

Answer 1

当您单击OK按钮时，我不确定您在做什么。我假设它向操作方法提交了一个表单，并且您将在某些usecase上再次将已发布的模型返回到视图(可能是在模型验证失败时吗？)。每当您将对象返回到视图时，都需要确保再次加载JPortalChanerUsersAsItems集合属性。因为Http是无状态的，并且它不会在多个请求之间持久化该属性的值。

[HttpPost]
public ActionResult SomeAction(PortalIndexView model)
{
   if(ModelState.IsValid)
   {
       // to do : Save and redirect
   }
   // Reload the collection.
   // I hard coded 2 items here. But you may get it from db and use it
   model.JPortalChamberUsersAsItems = new List<SelectListItem> {
     new SelectListItem { Value="1", Text="Detroit" } ,
     new SelectListItem { Value="2", Text="Ann Arbor" }
   };
   return View(model);

}