ASP.NET MVC NullReferenceException when returning view

Question

This was working and just up and quit one day when I sat down to work on it. I can't for the life of me figure it out. The error I'm getting is:

I can launch the application but as soon as I navigate to this page it kicks up the error while trying to display the view.

Here's my controller

 // 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();
    }

I've stepped through everything and all the data loads correctly from the DbContext and the list objets are exactly how I would expect right before I return the view.

Here's the view

@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...

I've stepped through each of the List objects above and each populates with the data I'm passing from the controller. I've also tried setting them all to null and the error still gets thrown in the same place. I also tried not passing anything back from the controller and it still happens.

@{
    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"];
}

I've also tried cleaning and rebuilding to no avail. If I remove the last line ("cssFiles") the error is thrown on the preceding line ("footers").

Full Stack Trace

   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)

Anyone know how I can troubleshoot this further or have dealt with this before?

@JamieRees - Those lists are populating dropdowns. The ID for each is what I need to know when I create a Form record. This is sitting on top of a 14 year old Oracle database and the tables don't have primary keys so mapping the VM to the Form model and just about any transaction with the database is painfully manual. I don't remember the exact reason for going this route now but it stemmed from that. I'm not opposed to revisiting if there's a good reason. This just ended up being cleaner. — Elliott, Jul 30 '15 at 16:43
That's very odd. The only logical cause of a `NullReferenceException` at that point in your code is if `ViewData` itself was null. If the value was null, you'd get a different exception, namely `InvalidCastException`, from trying to cast `null` to `List`. — Chris Pratt, Jul 30 '15 at 16:58
There's a *lot* of code here that is unlikely to be relevant to the issue. when debugging, exceptions in VS don't always stop where the actual error is (often the line after). Start by removing irrelevant code until you no longer get the error, then put that error line back and remove other code. This will give you the minimum code that's needed to demonstrate the error. Read this: http://stackoverflow.com/help/mcve — freedomn-m, Jul 30 '15 at 17:12
Looks similar to this question (the problem might be somewhere else): http://stackoverflow.com/q/13254539/1863970 — DavidC, Jul 30 '15 at 17:12
This probably won't may any difference to the error, but try removing the .sort (eg) `cssFiles.Sort();` - unless you've written your own Sort overload, sort on a ToList() will return `IOrderedEnumerable` - but you're not using the return value, so it probably is just getting ignored. Should be `cssFiles = cssFiles.Sort().ToList()`. — freedomn-m, Jul 30 '15 at 17:14

score 0 · Answer 1 · answered Jul 30 '15 at 19:18

By process of elimination I was able to resolve this. I don't know why it all of a sudden became an issue but the error was in fact in a different part of the view, lower down.

I was using traditional Html <input> tags and not ASP.NET's Html helper. By replacing this:

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

with this:

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

I was able to get the error to go away. I do not know why the traditional tags worked for a while then stopped however.

ASP.NET MVC NullReferenceException when returning view

1 Answers1