How to return a view for HttpNotFound() in ASP.Net MVC 3?

HttpNotFoundResult doesn't render a view. It simply sets the status code to 404 and returns an empty result which is useful for things like AJAX but if you want a custom 404 error page you could throw new HttpException(404, "Not found") which will automatically render the configured view in web.config:

<customErrors mode="RemoteOnly" redirectMode="ResponseRewrite">
   <error statusCode="404" redirect="/Http404.html" />
</customErrors>

This solution combines IResultFilter and IExceptionFilter to catch either thrown HttpException or returned HttpStatusCodeResult from within an action.

public class CustomViewForHttpStatusResultFilter: IResultFilter, IExceptionFilter
{
    string viewName;
    int statusCode;

    public CustomViewForHttpStatusResultFilter(HttpStatusCodeResult prototype, string viewName)
        : this(prototype.StatusCode, viewName) {
    }

    public CustomViewForHttpStatusResultFilter(int statusCode, string viewName) {
        this.viewName = viewName;
        this.statusCode = statusCode;
    }

    public void OnResultExecuted(ResultExecutedContext filterContext) {
        HttpStatusCodeResult httpStatusCodeResult = filterContext.Result as HttpStatusCodeResult;

        if (httpStatusCodeResult != null && httpStatusCodeResult.StatusCode == statusCode) {
            ExecuteCustomViewResult(filterContext.Controller.ControllerContext);

        }
    }

    public void OnResultExecuting(ResultExecutingContext filterContext) {
    }

    public void OnException(ExceptionContext filterContext) {
        HttpException httpException = filterContext.Exception as HttpException;

        if (httpException != null && httpException.GetHttpCode() == statusCode) {
            ExecuteCustomViewResult(filterContext.Controller.ControllerContext);
            // This causes ELMAH not to log exceptions, so commented out
            //filterContext.ExceptionHandled = true;
        }
    }

    void ExecuteCustomViewResult(ControllerContext controllerContext) {
        ViewResult viewResult = new ViewResult();
        viewResult.ViewName = viewName;
        viewResult.ViewData = controllerContext.Controller.ViewData;
        viewResult.TempData = controllerContext.Controller.TempData;
        viewResult.ExecuteResult(controllerContext);
        controllerContext.HttpContext.Response.TrySkipIisCustomErrors = true;            
    }
}

You can register this filter so, specifying either the http status code of the HttpException or the concrete HttpStatusCodeResult for which you want to display the custom view.

GlobalFilters.Filters.Add(new CustomViewForHttpStatusResultFilter(new HttpNotFoundResult(), "Error404"));
// alternate syntax
GlobalFilters.Filters.Add(new CustomViewForHttpStatusResultFilter(404, "Error404"));

It handles exceptions and HttpStatusCodeResult thrown or returned within an action. It won't handle errors that occur before MVC selects a suitable action and controller like this common problems:

• Unknown routes
• Unknown controllers
• Unknown actions

For handling these types of NotFound errors, combine this solution with other solutions to be found in stackoverflow.

Useful info from @Darin Dimitrov that HttpNotFoundResult is actually returning empty result.

After some study. The workaround for MVC 3 here is to derive all HttpNotFoundResult, HttpUnauthorizedResult, HttpStatusCodeResult classes and implement new (overriding it) HttpNotFound() method in BaseController.

It is best practise to use base Controller so you have 'control' over all derived Controllers.

I create new HttpStatusCodeResult class, not to derive from ActionResult but from ViewResult to render the view or any View you want by specifying the ViewName property. I follow the original HttpStatusCodeResult to set the HttpContext.Response.StatusCode and HttpContext.Response.StatusDescription but then base.ExecuteResult(context) will render the suitable view because again I derive from ViewResult. Simple enough is it? Hope this will be implemented in the MVC core.

See my BaseController bellow:

using System.Web;
using System.Web.Mvc;

namespace YourNamespace.Controllers
{
    public class BaseController : Controller
    {
        public BaseController()
        {
            ViewBag.MetaDescription = Settings.metaDescription;
            ViewBag.MetaKeywords = Settings.metaKeywords;
        }

        protected new HttpNotFoundResult HttpNotFound(string statusDescription = null)
        {
            return new HttpNotFoundResult(statusDescription);
        }

        protected HttpUnauthorizedResult HttpUnauthorized(string statusDescription = null)
        {
            return new HttpUnauthorizedResult(statusDescription);
        }

        protected class HttpNotFoundResult : HttpStatusCodeResult
        {
            public HttpNotFoundResult() : this(null) { }

            public HttpNotFoundResult(string statusDescription) : base(404, statusDescription) { }

        }

        protected class HttpUnauthorizedResult : HttpStatusCodeResult
        {
            public HttpUnauthorizedResult(string statusDescription) : base(401, statusDescription) { }
        }

        protected class HttpStatusCodeResult : ViewResult
        {
            public int StatusCode { get; private set; }
            public string StatusDescription { get; private set; }

            public HttpStatusCodeResult(int statusCode) : this(statusCode, null) { }

            public HttpStatusCodeResult(int statusCode, string statusDescription)
            {
                this.StatusCode = statusCode;
                this.StatusDescription = statusDescription;
            }

            public override void ExecuteResult(ControllerContext context)
            {
                if (context == null)
                {
                    throw new ArgumentNullException("context");
                }

                context.HttpContext.Response.StatusCode = this.StatusCode;
                if (this.StatusDescription != null)
                {
                    context.HttpContext.Response.StatusDescription = this.StatusDescription;
                }
                // 1. Uncomment this to use the existing Error.ascx / Error.cshtml to view as an error or
                // 2. Uncomment this and change to any custom view and set the name here or simply
                // 3. (Recommended) Let it commented and the ViewName will be the current controller view action and on your view (or layout view even better) show the @ViewBag.Message to produce an inline message that tell the Not Found or Unauthorized
                //this.ViewName = "Error";
                this.ViewBag.Message = context.HttpContext.Response.StatusDescription;
                base.ExecuteResult(context);
            }
        }
    }
}

To use in your action like this:

public ActionResult Index()
{
    // Some processing
    if (...)
        return HttpNotFound();
    // Other processing
}

And in _Layout.cshtml (like master page)

<div class="content">
    @if (ViewBag.Message != null)
    {
        <div class="inlineMsg"><p>@ViewBag.Message</p></div>
    }
    @RenderBody()
</div>

Additionally you can use a custom view like Error.shtml or create new NotFound.cshtml like I commented in the code and you may define a view model for the status description and other explanations.