how to render partial views to strings within controllers when using razor view engine with mvc4 
With webView (Aspx) i used :
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();
            }
        }
I tried that solution with razor , but it can't resolve the view, Error Message : 
The View can't be null => ViewResult.View
 
    