easp.netMVC nullReferenceException返回视图

Question

当我坐下来工作时，这是在工作，只是辞职了。我一生都不能弄清楚。我遇到的错误是：

我可以启动该应用程序，但是一旦我导航到此页面，它就会在尝试显示视图时踢出错误。

这里是我的控制器

 // GET: Form/Create
    public ActionResult Create()
    {
        List<METHOD> methods = new List<METHOD>();
        List<NATION> nations = new List<NATION>();
        List<LANGUAGE> languages = new List<LANGUAGE>();
        List<string> headers = new List<string>();
        List<string> footers = new List<string>();
        List<string> cssFiles = new List<string>();

        using(var context = new Entities(_connectionString))
        {

            // Get a list of methods to choose from incase they want to change the method
            methods = context.METHODs.ToList();

            // Get list of nations to choose from
            nations = context.NATIONs.OrderBy(x => x.NAME).ToList();

            // Get list of languages 
            languages = context.LANGUAGES.OrderBy(x => x.DESCRIPTION).ToList();

            // Get list of headers that are used today (from the DB...not solution)
            headers = context.WEB_CONTACT_DETAILs.Select(x => x.HDR_LINK).Distinct().ToList();
            headers.Sort();
            // Get list of footers that are used today (from the DB...not solution)
            footers = context.WEB_CONTACT_DETAILs.Select(x => x.FTR_LINK).Distinct().ToList();
            footers.Sort();
            // Get list of headers that are used today (from the DB...not solution)
            cssFiles = context.WEB_CONTACT_DETAILs.Select(x => x.CSS_LINK).Distinct().ToList();
            cssFiles.Sort();
        }
        ViewData["methods"] = methods;
        ViewData["nations"] = nations;
        ViewData["languages"] = languages;
        ViewData["headers"] = headers;
        ViewData["footers"] = footers;
        ViewData["cssFiles"] = cssFiles;

        return View();
    }

我已经从dbcontext正确加载了所有内容，并且列表objets正是我在返回视图之前的期望。

在这里是观点

@using Company.ContactFormAdmin.Web;
@using Company.ContactFormAdmin.Web.Models
@model FormViewModel
@{
    ViewBag.Title = "Edit";
    List<METHOD> methods = (List<METHOD>)ViewData["methods"];
    List<NATION> nations = (List<NATION>)ViewData["nations"];
    List<LANGUAGE> languages = (List<LANGUAGE>)ViewData["languages"];
    List<string> headers = (List<string>)ViewData["headers"];
    List<string> footers = (List<string>)ViewData["footers"];
    List<string> cssFiles = (List<string>)ViewData["cssFiles"]; //<--this is     where the exception is getting thrown.
}


<h2>New Contact Form</h2>
<div class="container"> //Truncated to keep it short...

我已经逐步介绍了上面的每个列表对象，并且每个列表对我从控制器传递的数据填充。我还尝试将它们全部设置为null，并且错误仍然被扔在同一位置。我还试图不从控制器中传递任何东西，但它仍然发生。

@{
    ViewBag.Title = "Edit";
    List<METHOD> methods = null;// (List<METHOD>)ViewData["methods"];
    List<NATION> nations = null;// (List<NATION>)ViewData["nations"];
    List<LANGUAGE> languages = null;// (List<LANGUAGE>)ViewData["languages"];
    List<string> headers = null;// (List<string>)ViewData["headers"];
    List<string> footers = null;// (List<string>)ViewData["footers"];
    List<string> cssFiles = null;// (List<string>)ViewData["cssFiles"];
}

我还尝试清洁和重建无济于事。如果我删除了最后一行（“ CSSFILES”），则将错误丢弃在上一行（“页脚”）上。 Full堆栈跟踪

   at ASP._Page_Views_Form_Create_cshtml.Execute() in c:\Projects\ConsumerServices\ContactFormAdmin\ContactFormAdmin_Soln-MVC-EB\ContactFormAdmin.Web\Views\Form\Create.cshtml:line 8
   at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
   at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
   at System.Web.WebPages.StartPage.RunPage()
   at System.Web.WebPages.StartPage.ExecutePageHierarchy()
   at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
   at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
   at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
   at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult)

任何人都知道我如何进一步解决问题或以前处理过？

通过消除过程，我能够解决这个问题。我不知道

为什么突然变成了一个问题，但是实际上，错误是在不同的部分，较低的地方。

I使用传统的HTML

<input>标签，而不是ASP.NET的HTML助手。通过更换此：

<input class="form-control" id="WEB_PAGE_NAME" name="WEB_PAGE_NAME" value="@Model.WEB_PAGE_NAME">

this：

@Html.TextBoxFor(model => model.WEB_PAGE_NAME, new { @class = "form-control" })

Answer 1

看起来像您已经使它起作用了。仅供参考：必须使用ViewData对象才能在视图中使用它。如果是无效的，它将丢失错误。在使用它以查看之前，请检查它是否未null，然后将其如下使用。

不起作用！

 <div>ViewData["cssFiles"]</div>

Works！

@if (ViewData["cssFiles"] != null)
{
    <div>ViewData["cssFiles"]</div>
}

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*强调文本

Answer 2

blockquote

list项目##标题##

Answer 3