public void Start()
        {
            ItemManager manager = new ItemManager();

            WrongInput += new PrintMessage(WrongInputErrorMessage);

            while (true)
            {
                Console.Clear();
                UserMenus.MainMenu();
                var input = Console.ReadKey(true).Key;

                switch (input)
                {
                case ConsoleKey.D1:
                    FilterMethod(manager);
                    break;

                case ConsoleKey.D2:
                    manager.AddNewProduct(this);
                    break;

                case ConsoleKey.D3:
                    Environment.Exit(0);
                    break;

                default: OnWrongInput("Not a valid input.");
                    break;
                }
            }
        }