不存在具有键“RouterElect”的“IEnumerable<SelectListItem>”类型的 ViewData 项

Question

这个问题之前曾被问过类似的问题，但我不确定如何将这些答案应用于我的具体问题：

视图模型

public string RouterElect { get; set; }

查看

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>

页面加载时渲染没有问题，如下所示：

但是，当选择下拉列表中的项目然后单击“确定”按钮时，会发生以下错误：

不存在具有键“RouterElect”的“IEnumerable”类型的 ViewData 项。

对于代码行：

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

任何想法都值得赞赏。

更新： 有人问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);
    }

还有一个关于 OKay 行动的问题。 它调用changeCurrentRouter脚本，该脚本执行ChangeCurrentRouter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“确定”按钮时，我不确定您在做什么。我假设它向操作方法提交表单，并且您在某些用例中再次将发布的模型返回到视图（可能是在模型验证失败时？）。每当您将对象返回到视图时，您都需要确保再次（重新）加载

JPortalChanerUsersAsItems

集合属性。因为 Http 是无状态的，它不会在多个请求之间保留该属性的值。

[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);

}