Implementing RenderPartialViewToString in ASP.NET MVC 3

To handle AJAX form requests in my ASP.NET MVC3 controller I needed a way to render a partial view to a string to return a JSON result containing both the (server-side) validation result (as boolean) and a rendered partial view (as string).

To avoid the need of a parent class for each controller that implements this (helper) method I decided to use the following extension methods:

/// <summary>
/// Controller extension class that adds controller methods
/// to render a partial view and return the result as string.
///
/// Based on http://craftycodeblog.com/2010/05/15/asp-net-mvc-render-partial-view-to-string/
/// </summary>
public static class ControllerExtension
{

/// <summary>
/// Renders a (partial) view to string.
/// </summary>
/// <param name="controller">Controller to extend</param>
/// <param name="viewName">(Partial) view to render</param>
/// <returns>Rendered (partial) view as string</returns>
public static string RenderPartialViewToString(this Controller controller, string viewName)
{
return controller.RenderPartialViewToString(viewName, null);
}

/// <summary>
/// Renders a (partial) view to string.
/// </summary>
/// <param name="controller">Controller to extend</param>
/// <param name="viewName">(Partial) view to render</param>
/// <param name="model">Model</param>
/// <returns>Rendered (partial) view as string</returns>
public static string RenderPartialViewToString(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())
{
var 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();
}
}

}