[ASP .NET MVC] Maintain ModelState errors using ActionFilterAttributes when applying Post-Redirect-Get pattern.

HomeController.cs

using System;
using System.Diagnostics;
using System.IO;
using System.Web;
using System.Web.Mvc;

using DemoApp.Models;
using Infrastructure.WebMvc;

namespace DemoApp.Controllers
{
  public class HomeController : Controller{
    
    [HttpGet]
    [RestoreModelStateFromTempData]
    public ActionResult Index(){
      ViewBag.SubmitResponse = TempData["SubmitResponse"];
      return View();
    }
    
    [HttpPost]
    [SetTempDataModelState]
    public ActionResult Submit(NewUser newUser, HttpPostedFileBase imageFileUpload){
      if (!ModelState.IsValid){
        return RedirectToAction("index"");
      }
      
      try{
        // Do process against the model (e.g. Store the model into database)
        
        ModelState.Clear();
      }
      catch(Exception exception){
        Trace.TraceError("Error message:'{0}'. Stack trace: '{1}'", exception.Message, exception.StackTrace);
        ModelState.AddModelError(string.Empty, string.Format("Creating a new user is Failed. Reason: '{0}'", exception.Message));
      }
      
      return RedirectToAction("Index");
    }
  }
}

RestoreModelStateFromTempDataAttribute.cs

using System.Web.Mvc;

namespace Infrastructure.WebMvc
{
    public class RestoreModelStateFromTempDataAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            base.OnActionExecuted(filterContext);
            if (filterContext.Controller.TempData.ContainsKey("ModelState"))
            {
                filterContext.Controller.ViewData.ModelState.Merge(filterContext.Controller.TempData["ModelState"] as ModelStateDictionary);
            }
        }
    }
}

SetTempDataModel.cs

using System.Web.Mvc;

namespace Infrastructure.WebMvc
{
    public class SetTempDataModelStateAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            base.OnActionExecuted(filterContext);
            filterContext.Controller.TempData["ModelState"] = filterContext.Controller.ViewData.ModelState;
        }
    }
}