Question

Getting an error in my (at this stage) simple c# MVC3 (Razor) application, and I can’t seem to find out what is causing the error below.

[InvalidOperationException: Sequence contains no elements]
   System.Linq.Enumerable.Last(IEnumerable`1 source) +4188046
   RouteDebug.RouteDebuggerHttpModule.OnBeginRequest(Object sender, EventArgs e) +78
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +148
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

this is all I get, no line numbers, no nothing.

I’ve tried putting breakpoints in various locations in the code, including the application_start sectin of Global.asax.cs, but these never get hit, the program just immediately bombs out with the stack trace as soon as i start debugging.

The structure of the application is as follows:

[Application.Core]
+Properties
+Reference
+Controllers
+Helpers
+Models
+AdminAreaRegistration.cs
+Global.asax.cs
[Application.Tests]
[Application.UI]
+Properties
+References
+App_Data
+Areas
    +Admin
        +Views
+Assets (css/js/images)
+Views

I’ve tried a few suggestions already, including adding the Application.Core namespace to the AdminAreaRegistration.cs file, and removing obj/bin and rebuilding.

I just can’t see whats causing the problem.

Update

AdminAreaRegistration.cs

using System.Web.Mvc;

namespace Application.Core
{
    public class AdminAreaRegistration : AreaRegistration
    {
        public override string AreaName
        {
            get
            {
                return "Admin";
            }
        }

        public override void RegisterArea(AreaRegistrationContext context)
        {
            context.MapRoute(
                "Admin_default",
                "Admin/{controller}/{action}/{id}",
                new {controller = "Page", action = "Index", id = UrlParameter.Optional }
            );
        }
    }
}

Global.asax.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Routing;

namespace Application.Core
{
    // Note: For instructions on enabling IIS6 or IIS7 classic mode, 
    // visit http://go.microsoft.com/?LinkId=9394801

    public class MvcApplication : System.Web.HttpApplication
    {
        public static void RegisterGlobalFilters(GlobalFilterCollection filters)
        {
            filters.Add(new HandleErrorAttribute());
        }

        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

            routes.MapRoute(
                "Default", // Route name
                "{controller}/{action}/{id}", // URL with parameters
                new { controller = "Page", action = "Homepage", id = UrlParameter.Optional } // Parameter defaults
            );

        }

        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();

            RegisterGlobalFilters(GlobalFilters.Filters);
            RegisterRoutes(RouteTable.Routes);
        }
    }
}

Answer 1

Glancing at RouteDebugger in reflector, the offending code is:

private static void OnBeginRequest(object sender, EventArgs e)
{
    if (RouteTable.Routes.Last<RouteBase>() != DebugRoute.Singleton)
    {
        RouteTable.Routes.Add(DebugRoute.Singleton);
    }
}

So: it sounds like somehow you have no routes. However, I would also wonder whether this module should actually use LastOrDefault, or basically cope better with this scenario.

Have you ensured that you have the current and up-to-date version of RouteDebugger ?

As for why you have no routes: maybe the pipeline is running in a different order now? First thing to do: remove that module and see if everything else works. If the site works fine minus that module, then ask Phil about it.