public class ViewBag : DynamicObject {

        private readonly  Dictionary<string,dynamic> dic=new  Dictionary<string,dynamic>(); 

        public ViewBag() {

        }

        private Dictionary<string,dynamic> ViewData {

            get {

                return dic;

            }

        }

        public override IEnumerable<string> GetDynamicMemberNames() {

            return ViewData.Keys;

        } 

        public override bool TryGetMember(GetMemberBinder binder, out object result) {

            result = ViewData[binder.Name];

            return true;

        }

        public override bool TrySetMember(SetMemberBinder binder, object value) {

            ViewData[binder.Name] = value;

            return true;

        }

    }

 dynamic viewBag = new ViewBag();

viewBag.Title="xxx";

Console.WriteLine(viewBag.Title);