There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key 'CategoryID - asp.net-mvc

Question

I have found a lot of similar threads on this problem. But whatever I do, it never works for me.
The ONLY thing I want to achieve right now, is to fill a dropdown list with database values in a partial view, that's within a partial view. That is all, and this is driving me absolutely nuts. A user should be able to chose a category name in the dropdown list.
Here's my Controller Class:
public class AttributeController : Controller
{
private readonly IRepository<ClassLibrary.Entities.Attribute> _aRepository;
private readonly IRepository<Category> _cRepository;
public AttributeController() : this(new Repository<ClassLibrary.Entities.Attribute>(), new Repository<Category>())
{
}
public AttributeController(IRepository<ClassLibrary.Entities.Attribute> repo, IRepository<Category> repository)
{
_aRepository = repo;
_cRepository = repository;
}
//
// GET: /Attribute/
public ActionResult Index()
{
var attributes = _aRepository.GetAll();
var attributeViewModels = new List<AttributeViewModel>();
foreach (ClassLibrary.Entities.Attribute attribute in attributes)
{
var viewModel = new AttributeViewModel();
viewModel.Id = attribute.Id;
viewModel.AttributeName = attribute.Name;
attributeViewModels.Add(viewModel);
}
return View(attributeViewModels);
}
//
// GET: /Attribute/Details/5
public ActionResult Details(int id)
{
return View();
}
//
// GET: /Attribute/Create
public ActionResult Create()
{
ViewData["CategoryID"] = new SelectList(_cRepository.GetAll().ToList(), "Category_id", "Category");
IEnumerable<SelectListItem> items = _cRepository.GetAll().Select(c => new SelectListItem
{
Value = c.Id.ToString(),
Text = c.Name
});
ViewData["CategoryID"] = items;
return View();
}
//
// POST: /Attribute/Create
[HttpPost]
public ActionResult Create(FormCollection collection)
{
try
{
// TODO: Add insert logic here
return RedirectToAction("Index");
}
catch
{
return View();
}
}
And here's the index View:
#model IEnumerable<GUI.Models.AttributeViewModel>
#{
ViewBag.Title = "Attributes";
}
<div>
#Html.Partial("~/Views/Attribute/Create.cshtml", new GUI.Models.AttributeViewModel())
</div>
<h2>All existing Attributes</h2>
<table class="table">
<tr>
<th>
#Html.DisplayNameFor(model => model.AttributeName)
</th>
<th></th>
</tr>
#if(Model != null)
{
foreach (var item in Model) {
<tr>
<td>
#Html.DisplayFor(modelItem => item.AttributeName)
</td>
<td>
#Html.ActionLink("Edit", "Edit", new { id=item.Id }) |
#Html.ActionLink("Details", "Details", new { id=item.Id }) |
#Html.ActionLink("Delete", "Delete", new { id=item.Id })
</td>
</tr>
}
}
</table>
Here's the partial View Within the index view:
#model GUI.Models.AttributeViewModel
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
<div class="form-horizontal">
<h4>Create an attribute for this Category</h4>
<hr />
#Html.ValidationSummary(true)
<div class="form-group">
#Html.Partial("~/Views/Attribute/CategoryPartial.cshtml", new GUI.Models.CategoryViewModel())
<div class="form-group">
#Html.LabelFor(model => model.AttributeName, new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.EditorFor(model => model.AttributeName)
#Html.ValidationMessageFor(model => model.AttributeName)
</div>
</div>
</div>
</div>
}
#section Scripts {
#Scripts.Render("~/bundles/jqueryval")
}
And finally CategoryPartialView within the partial view that will contain the DropDown List where the user should be able to select a category Name.
#model GUI.Models.CategoryViewModel
#using GUI.Controllers
#using System.Collections.Generic
#{
//var categories = (IEnumerable<GUI.Models.CategoryViewModel>)ViewData["categories"];
}
#using (Html.BeginForm())
{
#Html.AntiForgeryToken()
<hr />
#Html.ValidationSummary(true)
<div class="form-group">
#Html.LabelFor(model => model.Name, new { #class = "control-label col-md-2" })
<div class="col-md-10">
#Html.DropDownList("CategoryID", (IEnumerable<SelectListItem>)ViewData["CategoryID"])
</div>
</div>
}
The exception ALWAYS occurs when I'm debugging the application and it points to the #Html.DropDownList part. Claiming that "There is no ViewData item of type 'IEnumerable' that has the key 'CategoryID".
#Html.DropDownList("CategoryID", (IEnumerable<SelectListItem>)ViewData["CategoryID"]
I'm sorry for posting so many code blocks. But I would really like to solve this.I've beaten my head against the wall for hours with frustration, and any help would be greatly appreciated.

Answer 1

When you use #Html.Partial("~/Views/Attribute/CategoryPartial.cshtml", new GUI.Models.CategoryViewModel()) you are directly instantiating the partial view. The controller does not get called and is not responsible for generating the HTML markup string. Additionally, you are passing an empty view model (new GUI.Models.CategoryViewModel()). Since the controller does not get called, it does not get the data for the drop down list and, obviously, does not save it in your ViewData.
Use the #Html.Action helper instead:
<div class="form-group">
#Html.Action("Create", "Attribute")
<div class="form-group">
Change the Create action like this:
//
// GET: /Attribute/Create
public ActionResult Create()
{
ViewData["CategoryID"] = new SelectList(_cRepository.GetAll().ToList(), "Category_id", "Category");
IEnumerable<SelectListItem> items = _cRepository.GetAll().Select(c => new SelectListItem
{
Value = c.Id.ToString(),
Text = c.Name
});
ViewData["CategoryID"] = items;
return PartialView("CategoryPartial", new GUI.Models.CategoryViewModel());
}
Note: I don't know your entire structure, but I might be best to use this approach and to return a Lis<SelectListItem> model.

Answer 2

when calling:
#Html.Partial("~/Views/Attribute/Create.cshtml", new GUI.Models.AttributeViewModel())
you call the view directly with out passing throw the controller so the model you have there is an empty model!
try pass throw the controller to create you'r model and send it back as a view:
#Html.RenderPartial("YOUR CONTROLLER",model);