Cascading Dropdown using Stored Procedure in asp.net mvc

  public class ItemController : Controller
{

    DB_ITEMEntities db = new DB_ITEMEntities();       

    public ActionResult Index()
    {
        ViewBag.catVG =new SelectList( db.SP_BIND_CATEGORY(),"CATID","CATNAME");
                   
        return View();
    }

    public JsonResult GetSubcat(int catid)
    {
       var subcat = db.SP_BIND_SUBCAT_BY_CAT(catid);
        return Json(new SelectList(subcat, "SUBCATID", "SUBCATNAME"));
       
    }
}

    Category
    @Html.DropDownList("ddlCat", ViewBag.catVG as SelectList,new { style = "width:100px" })

        SubCategory
       @Html.DropDownList("ddlSubCat", new SelectList(string.Empty, "Value", "Text"), "Please select a Sub Category", new { style = "width:100px" })