Returning a rendered HTML partial in a JSON Property in ASP.NET MVC

Here is some code that will work cause I needed to do this today. The original code is described here.

public static string RenderPartialToString(string controlName, object viewData)
{
    var viewContext = new ViewContext();
    var urlHelper = new UrlHelper(viewContext.RequestContext);
    var viewDataDictionary = new ViewDataDictionary(viewData);

    var viewPage = new ViewPage
    {
        ViewData = viewDataDictionary,
        ViewContext = viewContext,
        Url = urlHelper
    };

    var control = viewPage.LoadControl(controlName);
    viewPage.Controls.Add(control);

    var sb = new StringBuilder();
    using (var sw = new StringWriter(sb))
    using (var tw = new HtmlTextWriter(sw))
    {
            viewPage.RenderControl(tw);
    }

    return sb.ToString();
}

You can then use it to do RJS style json results

public virtual ActionResult Index()
{
    var jsonResult = new JsonResult
    {
        Data = new
        {
            main_content = RenderPartialToString("~/Views/contact/MyPartial.ascx", new SomeObject()),
            secondary_content = RenderPartialToString("~/Views/contact/MyPartial.ascx", new SomeObject()),
        }
    };

    return Json(jsonResult, JsonRequestBehavior.AllowGet);
}

And the partial has a strongly typed view model

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<SomeObject>" %>
<h1>My Partial</h1>