TempData null after return from Base Controller

Question

TempData is populated in the Base method, but turns to null as soon as the code returns back to the derived controller's method.

Derived Controller Edit Action (Post):

public class ManageItemsController : BaseController
{
        private BaseControllerSingle<Item, ItemViewModel> GetBaseControllerSingle()
        {
            return new BaseControllerSingle<Item, ItemViewModel>(_itemRepository, AreaName, ControllerName);
        }
...

    // POST: /InventoryMgmt/ManageItems/Edit/5
    [HttpPost]
    public ActionResult Edit(ItemViewModel ItemViewModel)
    {
        ItemViewModel = _manageItemsAppServ.SaveOrUpdate(ItemViewModel, CurrentCompanyId);

        return GetBaseControllerSingle().EditPost(
            ItemViewModel, 
            x => x.Id == ItemViewModel.Item.Id && x.CompanyId == CurrentCompanyId
        );
    }

Base Controller Edit Action:

public class BaseControllerSingle<TRepository, TViewModelSingle> : BaseController
        where TRepository : class, IEntity, IAuditStamps, new()
        where TViewModelSingle : class, IEntity, IViewModelSingle<TRepository, TViewModelSingle>, new()
    {
        ...

        public virtual ActionResult EditPost(
        TViewModelSingle viewModel,
        Expression<Func<TRepository, bool>> predicate = null
    )
    {
        if (ModelState.IsValid)
        {
            BaseAppServSingle<TRepository, TViewModelSingle> baseAppServSingle =
                new BaseAppServSingle<TRepository, TViewModelSingle>(_repository);

            ActionConfirmation<int> result = baseAppServSingle.SaveOrUpdate(
                viewModel,
                CurrentUserId,
                predicate
            );

            TempData["message"] = result.Message;

            if (result.WasSuccessful)
            {
                return RedirectToAction("Edit", new { id = result.Value });
            }
        }

        TempData["message"] = "There is invalid data on the form.";
        return View(viewModel);
    }

Answer 1

In the end I solved this by inheriting from the base controller instead of instantiating a new instance. The new instance I was creating must've messed with the TempData