Cascade Drop down list - asp.net-mvc-4

Question

I am trying to create a cascading drop down list, and I am getting an error.
This contains what I am try to do with in my controller class:
public ActionResult Create()
{
ViewBag.Status = new SelectList(db.pjt_Statuses, "pjt_Status_ID", "StatusName");
ViewBag.CategoryID = new SelectList(db.pjt_Categories, "pjt_Category_ID", "CatName");
return View();
}
public ActionResult SubCategory(int id)
{
var SubCategory = from s in db.pjt_SubCategories
where s.CategoryID == id
select s;
return Json(SubCategory.ToList());
}
// POST: /Project/Create
[HttpPost]
public ActionResult Create(pjt_Projects pjt_projects)
{
if (ModelState.IsValid)
{
pjt_projects.CreationDate = DateTime.Now;
db.pjt_Projects.Add(pjt_projects);
db.SaveChanges();
return RedirectToAction("Index");
}
ViewBag.Status = new SelectList(db.pjt_Statuses, "pjt_Status_ID", "StatusName", pjt_projects.Status);
ViewBag.CategoryID = new SelectList(db.pjt_Categories, "pjt_Category_ID", "CatName", pjt_projects.CategoryID);
return View(pjt_projects);
}
View
This shows what I am try to do on the front end. I am getting a error with the bold line in my view code below. The error I am getting is:
There is no ViewData item of type IEnumerable<SelectListItem> that has the key pjt_SubCat_ID.
Code:
<div class="span3 offset1">
#Html.LabelFor(model => model.CategoryID, "Category")
#Html.DropDownList("CategoryID", String.Empty)#*, null, new { #onchange = "FetchSubCategories();" })*#
<br />
#Html.ValidationMessageFor(model => model.CategoryID)
</div>
<div class="span3 offset1">
<label>Sub Category</label>
#Html.DropDownList("pjt_SubCat_ID", String.Empty)
<br />
#Html.ValidationMessageFor(model => model.SubCategoryID)
</div>
Can someone advise me what is going wrong here?

Answer 1

The problem is that the engine is trying to get the SelectList from the viewbag and it cannot find it. I am guessing that you want the Dropdown to display the items you have stored in the viewbag under "pjt_SubCat_ID" but you are not adding that item to the viewbag anywhere in the code that you have listed in your question.
If that is supposed to be the data returned from the SubCategory() method, you will not find that data in the viewbag and you should have a javascript that calls this method on the click event of the original SelectList (category id one) and binds the returned data to the subcategory one.