Handling 404 Error in ASP.NET MVC

In ASP.NET Web Forms, handling 404 errors are easy - which is basically a web.config setting. In ASP.NET MVC, it is a bit more complicated. Why is it more complicated? In comparison, everything is seemingly easier in MVC than WebForm.

It is more complicated mainly because of Routing. In WebForm, most 404 occurs because of non-existent file and each UR: is usually mapped to a particular file (aspx). With MVC, that is not the case. All requests are handled by the Routing table and based on that it will invoke appropriate controller and actions etc. Secondly, our basic default route usually is quite common ({controller}/{action}/{id}) - therefore most URL request will be caught by this route.

So, let's dive in on how can we do proper handling of 404 errors with ASP.NET MVC.

TURN ON CUSTOM ERROR IN WEB.CONFIG

    <customErrors mode="On" defaultRedirect="~/Error/Error">
      <error statusCode="404" redirect="~/Error/Http404" />
    </customErrors>

DECLARE  DETAIL ROUTES MAPPED IN ROUTE TABLE

So instead of just using the default route:

   routes.MapRoute(
      name: "Default",
      url: "{controller}/{action}/{id}",
      defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
   );

Declare all your intended route explicitly and create a "catch-all" to handle non-matching route - which basically a 404. In MVC, a 404 can happen when you try to access a URL where the there is no controller for. This code in the routing table handles that scenario.

   routes.MapRoute(
      name: "Account",
      url: "Account/{action}/{id}",
      defaults: new { controller = "Account", action = "Index", id = UrlParameter.Optional }
   );

   routes.MapRoute(
      name: "Home",
      url: "Home/{action}/{id}",
      defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
   );

   routes.MapRoute(
      name: "Admin",
      url: "Admin/{action}/{id}",
      defaults: new { controller = "Admin", action = "Index", id = UrlParameter.Optional }
   );

   routes.MapRoute(
      name: "404-PageNotFound",
      url: "{*url}",
      defaults: new { controller = "Home", action = "Http404" }
   );

OVERRIDE HANDLEUNKNOWNACTION IN BASECONTROLLER CLASS

Create a Controller base class that every controller in your application inherits from. In that base controller class, override HandleUnknownAction method. Now, another scenario that a 404 may happen is that when the controller exists, but there is no action for it. In this case, the routing table will not be able to trap it easily - but the controller class has a method that handle that.

    [AllowAnonymous]
    public class ErrorController : Controller
    {
        protected override void HandleUnknownAction(string actionName)
        {
            if (this.GetType() != typeof(ErrorController))
            {
                var errorRoute = new RouteData();
                errorRoute.Values.Add("controller", "Error");
                errorRoute.Values.Add("action", "Http404");
                errorRoute.Values.Add("url", HttpContext.Request.Url.OriginalString);
 
                View("Http404").ExecuteResult(this.ControllerContext);
            }
        }
 
        public ActionResult Http404()
        {
            return View();
        }
 
        public ActionResult Error()
        {
            return View();
        }
    }

CREATE CORRESPONDING VIEWS

View for generic error: Error.chtml

@model System.Web.Mvc.HandleErrorInfo
 
@{
    ViewBag.Title = "Error";
}
 
<hgroup class="title">
    <h1 class="error">Error.</h1>
    <br />
    <h2 class="error">An error occurred while processing your request.</h2>
    @if (Request.IsLocal)
    {
        <p>
            @Model.Exception.StackTrace
        </p>
    }
    else
    {
        <h3>@Model.Exception.Message</h3>
    }
</hgroup>

View for 404 error: Http404.chtml

@model System.Web.Mvc.HandleErrorInfo
 
@{
    ViewBag.Title = "404 Error: Page Not Found";
}
<hgroup class="title">
    <h1 class="error">We Couldn't Find Your Page! (404 Error)</h1><br />
    <h2 class="error">Unfortunately, the page you've requested cannot be displayed. </h2><br />
    <h2>It appears that you've lost your way either through an outdated link <br />or a typo on the page you were trying to reach.</h2>    
</hgroup>