Extensions methods to create a top level menu based on areaname convention

gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Text;
using System.Reflection;

namespace TopMenuBasedOnAreas.HtmlHelpers
{
    public static class TopMenuExtensions
    {
        private static IEnumerable<string> _areaNames;

        public static MvcHtmlString RenderTopMenuItems(this HtmlHelper helper)
        {
            var areaNames = GetAreaNames();
            var currentArea = helper.ViewContext.RouteData.DataTokens["area"] as string;

            var html = new StringBuilder();
            foreach (var areaName in areaNames)
            {
                var urlHelper = new UrlHelper(helper.ViewContext.RequestContext);
                var url = urlHelper.Action(string.Empty, string.Empty, new { area = areaName });
                // var url = urlHelper.RouteUrl(areaName + "_default");

                html.AppendLine(areaName.Equals(currentArea, StringComparison.OrdinalIgnoreCase) ? "<li class='active'>" : "<li>");
                html.AppendLine(string.Format("<a href='{0}'>{1}</a>", url, areaName));
                html.AppendLine("</li>");
            }

            return new MvcHtmlString(html.ToString());
        }

        private static IEnumerable<string> GetAreaNames()
        {
            if (_areaNames == null)
            {
                _areaNames = Assembly
                    .GetExecutingAssembly()
                    .GetTypes()
                    .Where(t => t.IsClass && typeof(AreaRegistration).IsAssignableFrom(t))
                    .Select(a => (AreaRegistration)Activator.CreateInstance(a))
                    .Select(r => r.AreaName);
            }

            return _areaNames;
        }
    }
}