How to update a textarea in the current view on Submit in ASP.net MVC 3?

I have a page that has two drop down lists and based upon the selection of these two lists I would like to populate a textarea with some data on submit button press.

The behavior that I am seeing while debugging开发者_如何学Go is that the page is rendered, I make my selections and press submit. The DataAccess returns the correct results and the View returns, but with an exception "There is no ViewData item of type 'IEnumerable' that has the key 'People'.

I can see that I could re-setup the drop down lists, but it feels like I'm approaching this incorrectly. Is there another approach for doing this sort of action in MVC 3?

 public ActionResult Test()
    {
        //People for dropdownlist 1
        var db = peopleRepository.People;
        var query = db.Select(c => new {c.Id, c.Name});
        ViewBag.People = new SelectList(query.AsEnumerable(), "Id", "Name");

        //Elements for dropdownlist 2
        var list = new Dictionary<string, string> {{"1", "Name"}, {"2", "Address"}, {"3", "Zip"}};
        ViewBag.Elements = new SelectList(list, "Key", "Value");

        return View();
    }

 // This part is what I'm confused about.
[AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Test(string people, string elements)
    {
        if (ModelState.IsValid)
        {
            // Output from persistent storage query
            var da = new DatabaseAccess(people, elements);
            ViewBag.Results = da.Execute();

        }
        return View();
    }

View:

@using (Html.BeginForm("Test", "Home", FormMethod.Post))

{ @Html.DropDownList("People", (SelectList)ViewBag.People, "--Select One--") @Html.DropDownList("Elements", (SelectList)ViewBag.Elements, "--Select One--") @Html.TextArea("Results", (string)ViewBag.Results, 10, 120, "") }

---

Here is how I would quickly construct it :

Model :

   public class People
   {
      public int Id { get; set; }
      public string Name { get; set; }
   }

ViewModel (everything needed by the view):

   public class TestViewModel
   {

      public int SelectedPeopleId { get; set; }

      public string SelectedElementId { get; set; }

      public SelectList People { get; set; }
      public SelectList Elements { get; set; }
      public String Results { get; set; }

   }

Controller (used Index as the default Action, create an init function for the view model that can be adapted)to anything more appropriate :

public class HomeController : Controller
   {

      private static TestViewModel InitTestVM()
      {
         //People for dropdownlist 1
         var db = new List<People>();//peopleRepository.People;
         db.Add(new People { Id = 1, Name = "Name 1" });
         db.Add(new People { Id = 2, Name = "Name 2" });
         var query = db.Select(c => new { c.Id, c.Name });

         //Elements for dropdownlist 2
         var list = new Dictionary<string, string> { { "1", "Name" }, { "2", "Address" }, { "3", "Zip" } };


         TestViewModel testVM = new TestViewModel
         {
            People = new SelectList(query.AsEnumerable(), "Id", "Name"),
            Elements = new SelectList(list, "Key", "Value")
         };
         return testVM;
      }

      public ActionResult Index()
      {
         return View(InitTestVM());
      }

      // This part is what I'm confused about.
      [AcceptVerbs(HttpVerbs.Post)]
      public ActionResult Index(TestViewModel testVM)
      {
         var vm = InitTestVM();
         if (ModelState.IsValid && testVM != null)
         {
            ModelState.Clear();
            // Output from persistent storage query
            //var da = new DatabaseAccess(people, elements);
            vm.Results = "sfdfsdfsdfsdfsdfsdfsdfsdf";//da.Execute();
            vm.SelectedElementId = testVM.SelectedElementId;
            vm.SelectedPeopleId = testVM.SelectedPeopleId;
            return View(vm);
         }
         return View(vm);
      }
   }

And finally the View :

@model ViewModels.TestViewModel

@using (Html.BeginForm("Index", "Home", FormMethod.Post))
{ 
   @Html.DropDownListFor(m => m.SelectedPeopleId, Model.People, "--Select One--") 
   @Html.DropDownListFor(m => m.SelectedElementId, Model.Elements, "--Select One--") 
   @Html.TextAreaFor(m => m.Results, 10, 120, "") 
   <input type="submit" value="Test" />
}