Question

Im new to MVC2/3 so keep that in mind. Also, using Ajax or jQuery is NOT an option.

I have a web page where the user must choose an item out of a dropdown list and then hit a “Filter” button. (Clicking this button will simply trigger the default POST action in my controller and return a filtered list of results.

I have everything working except I am running into one issue. When the Filter action is complete and returns control back to my view, the dropdown list contents are lost (ie, null). The results are returned no problem, it’s just that my dropdown list is blank – thus preventing user from selecting another item out of the list.

Am I supposed to re-fill the dropdown list on the Filter action or is there a cleaner way to do this?

Here is a snapshot of my code:

My ViewModel

public class MyViewModel {
        [DisplayName("Store")]
        public IEnumerable<Store> StoreList { get; set; }

        public string SelectedStore { get; set; }
}

My View (Index.cshtml)

@using (Html.BeginForm()) {

    <h2>Search</h2>

    @Html.LabelFor(m => m.StoreList)
    @Html.DropDownListFor(m => m.SelectedStore, new SelectList(Model.StoreList, "StoreCode", "StoreCode"), "Select Store")

    <input type="submit" value="Filter" />
}

My Controller:

public class MyController : Controller
{
        public ActionResult Index() {

            MyViewModel vm = new MyViewModel();
            var storelist = new List<Store>();
            storelist.Add(new Store { StoreCode = "XX" });
            storelist.Add(new Store { StoreCode = "YY" });
            storelist.Add(new Store { StoreCode = "ZZ" });
            vm.StoreList = storelist;

            return View(vm);
        }

        [HttpPost]
        public ActionResult Index(MyViewModel model, string SelectedStore, FormCollection collection) {

            if (ModelState.IsValid) {
                /* this works, model state is valid */

                /* BUT, the contents of model.StoreList is null */
            } 

            return View( model);
        }
}

Answer 1

Yes, you have to repopulate any models (including ViewData) that are passed to the view. Remember, it’s a stateless system, your controller is re-instantiated with every call and starts effectively from scratch.

I would do it thus:

public class MyController : Controller
{
     private List<Store> GetStoreList()
     {
          List<Store> StoreList = new List<Store>();
          // ... Do work to populate store list
          return StoreList;
     }

     public ActionResult Index() {

         MyViewModel vm = new MyViewModel();
         vm.StoreList = GetStoreList();
         return View(vm);
     }

     [HttpPost]
     public ActionResult Index(MyViewModel model, string SelectedStore, FormCollection collection) {

         if (ModelState.IsValid) {
            /* this works, model state is valid */

            /* BUT, the contents of model.StoreList is null */
         } 
         model.StoreList = GetStoreList();
         return View( model);
     }
}