为什么我的第二个下拉列表不会加载任何值？

Question

我是编程的初学者，我在过去的3天里陷入困境，所以我希望你的帮助：）

我在同一视图中创建了2个下拉列表，项目类型和项目。

第一个下拉列表（项类型）中的值加载正常，我要做的是当您从该列表中选择一个值以填充具有相关值的第二个下拉列表（Items）时。

此刻一直空着......

我做错了什么？ ：（

这是我的代码：

查看：

@using (Html.BeginForm("Browse", "Bookings", FormMethod.Post, new { id = "TypeItemFormID", data_itemsListAction = @Url.Action("ItemsList") }))
{
<fieldset>
    <legend> Type/Item</legend>
    @Html.DropDownList("department", ViewBag.ItemTypesList as SelectList, "Select a Type", new {id="ItemTypeID"})
    <div id="ItemsDivId">
        <label for="Items">Items </label>
        <select id="ItemsID" name="Items"></select>
    </div>
    <p>
        <input type ="submit" value="Submit" id="SubmitID" />
    </p>
 </fieldset>
}
<script src ="@Url.Content("~/Scripts/typeItems.js")"></script>

控制器：

public class BookingsController : Controller
    {

        private BookingSystemEntities db = new BookingSystemEntities();
        //
        // GET: /Bookings/

        public ActionResult Index()
        {
            ViewBag.Message = "Select your Department";
            var departments = db.Departments.ToList();
            return View(departments);
        }

        public ActionResult Browse(string department, string ID)
        {

            ViewBag.Message = "Browse for Equipment";

           var departments = db.Departments.Include("Items").Single(i => i.DepartmentName == department);

           ViewBag.ItemTypesList = GetItemTypeSelectList(department);

           return View();

        }

        public ActionResult Details(int id)
        {
            var item = db.Items.Find(id);

            return View(item);
        }

        //
        // GET: /Home/DepartmentMenu
        [ChildActionOnly]
        public ActionResult DepartmentMenu()
        {
            var departments = db.Departments.ToList();
            return PartialView(departments);
        }


        public SelectList GetItemTypeSelectList(string department)
        {
            var departments = db.Departments.Include("Items").Single(i => i.DepartmentName == department);
            List<SelectListItem> listItemTypes = new List<SelectListItem>();
            foreach (var item in departments.Items.Select(s => s.ItemType.ItemTypeName).Distinct())
            {
                listItemTypes.Add(new SelectListItem
                {
                    Text = item,
                    Value = item,
                }

                     );
            }

            return new SelectList(listItemTypes.ToArray(),
                                "Text",
                                "Value");

        }

        public ActionResult ItemsList(string ID)
        {
            string Text = ID;
            var items = from s in db.Items
                        where s.ItemType.ItemTypeName == Text
                        select s;

            if (HttpContext.Request.IsAjaxRequest())
                return Json(new SelectList(
                                items.ToArray(),
                                "ItemId",
                                "ItemName")
                           , JsonRequestBehavior.AllowGet);

            return RedirectToAction("Browse");
        } 


    }

Javascript：

$(function () {

    $('#ItemsDivId').hide();
    $('#SubmitID').hide();

    $('#ItemTypeID').change(function () {
        var URL = $('#TypeItemFormID').data('itemsListAction');
        $.getJSON(URL + '/' + $('#ItemTypeID').val(), function (data) {
            var items = '<option>Select a Item</option>';
            $.each(data, function (i, item) {
                items += "<option value='" + item.Value + "'>" + item.Text + "</option>";
                // state.Value cannot contain ' character. We are OK because state.Value = cnt++;
            });
            $('#ItemsID').html(items);
            $('#ItemsDivId').show();

        });
    });

    $('#ItemsID').change(function () {
        $('#SubmitID').show();
    });
});

最后我的模特：

public class Department
    {
        public int DepartmentId { get; set; }

        [DisplayName("Department")]
        public string DepartmentName { get; set; }

        public List<Item> Items { get; set; }

    }

public class ItemType
    {
        public int ItemTypeId { get; set; }

        [DisplayName("Type")]
        public string ItemTypeName { get; set; }

        [DisplayName("Image")]
        public string ItemTypeImage { get; set; }

        public List<Item> Items { get; set; }

    }

 public class Item
    {
        public int ItemId { get; set; }

        [DisplayName("Name")]
        public string ItemName { get; set; }

        [DisplayName("Description")]
        public string ItemDescription { get; set; }

         [DisplayName("Ref Code")]
        public string ItemReferenceCode { get; set; }

        [ForeignKey("ItemType")]
        public int ItemTypeId { get; set; }
        public virtual ItemType ItemType { get; set; }

        [ForeignKey("Department")]
        public int DepartmentId { get; set; }
        public Department Department { get; set; }

        [DisplayName("Computer Location")]
        public string ComputerLocation { get; set; }

        [DisplayName("Author Name")]
        public string AuthorName { get; set; }

        [DisplayName("Published Year")]
        public string PublishedYear { get; set; }

    }