Knockout and InitializeViewBag method (MVC)

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Knockout.js

Hi!
Visual studio doesn't understand method InitializeViewBag("Simple list") from example below. Please, help

Model

public class SimpleListModel
{
public string ItemToAdd { get; set; }
public List<string> Items { get; set; }

public void AddItem()
{
Items.Add(ItemToAdd);
ItemToAdd = "";
}
}

Razor

@using PerpetuumSoft.Knockout
@model KnockoutMvcDemo.Models.SimpleListModel
@{
var ko = Html.CreateKnockoutContext();
}
@using (ko.Html.Form("AddItem", "SimpleList", null, new { id = "myform" }))
{
<span>New item:</span>
@ko.Html.TextBox(m => m.ItemToAdd).ValueUpdate(KnockoutValueUpdateKind.AfterKeyDow n) 
<button type="submit" @ko.Bind.Enable(m => m.ItemToAdd.Length > 0)>Add</button>
<p>Your items:</p>
@ko.Html.ListBox(m => m.Items, new { width = 50, size = 7 }) 
} 
<script type="text/javascript"> 
$('#myform').ajaxForm();
</script> 

@ko.Apply(Model)

Controller

public class SimpleListController : BaseController
{
public ActionResult Index()
{
InitializeViewBag("Simple list");
var model = new SimpleListModel { Items = new List<string> { "Alpha", "Beta", "Gamma" } };
return View(model);
}

public ActionResult AddItem(SimpleListModel model)
{
model.AddItem();
return Json(model);
}
}