How do I maintain ModelState errors when using RedirectToAction?

Question

I have some code that saves a ticket in our system. If there is an error it does a RedirectToAction. The problem is that I don\'t seem to have my errors in the new action.

Answer 1

What I did to maintain my ModelState no matter where I go with redirects is the following:

1. In your model, add:

   public ModelStateDictionary modelstate { get; set; }
   

2. In your model's constructor, add:

   this.modelstate = new System.Web.Mvc.ModelStateDictionary();
   

3. Sample Post with my model called Models.ContactInformation:

   [HttpPost]
   [ValidateAntiForgeryToken]
   public ActionResult contact(Models.ContactInformation con)
   {
     if (string.IsNullOrEmpty(con.SelectedAgencySelectorType))
     {
       ModelState.AddModelError("", "You did not select an agency type.");
     }
   
     con.modelstate = ModelState;
     TempData["contact"] = con;
     if (!ModelState.IsValid) return RedirectToAction("contactinformation", "reports");
   
       //do stuff
   
       return RedirectToAction("contactinformation", "reports");
   }
   

4. So now your tempdata has your model and modelstate as is.

5. The following is my view that is agnostic to the state of anything, unless it has something. Here's the code:

   [HttpGet]
   public ActionResult contactinformation()
   {
       //try cast to model
       var m = new Models.ContactInformation();
       if (TempData["contact"] is Models.ContactInformation) m = (Models.ContactInformation)TempData["contact"];
   
       //restore modelstate if needed
       if (!m.modelstate.IsValid)
       {
           foreach (ModelState item in m.modelstate.Values)
           {
               foreach (ModelError err in item.Errors)
               {
                   ModelState.AddModelError("", err.ErrorMessage.ToString());
               }
           }
       }
   
       return View(m);
   }