"How to series" about MVC, jQuery, JSON, paging, mapRoute

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

namespace AddressBook_mvc3_jQuery.Helpers
{
    public static class RenderLib
    {
        public static string RenderPartialView(this Controller controller, string viewName, object model)
        {
            if (string.IsNullOrEmpty(viewName))
                viewName = controller.ControllerContext.RouteData.GetRequiredString("action");

            controller.ViewData.Model = model;
            using (var sw = new StringWriter())
            {
                ViewEngineResult viewResult = ViewEngines.Engines.FindPartialView(controller.ControllerContext, viewName);
                var viewContext = new ViewContext(controller.ControllerContext, viewResult.View, controller.ViewData, controller.TempData, sw);
                viewResult.View.Render(viewContext, sw);

                return sw.GetStringBuilder().ToString();
            }
        }

    }
}