public void RemoveListener(FormDataEventHandler handler)
 {
     if (handlers.ContainsKey(handler.Id))
     {
         handlers.Remove(handler.Id);
     }
 }
        public void AddListener(FormDataEventHandler handler)
        {
            if (handler == null)
            {
                throw new ArgumentNullException(nameof(handler));
            }

            handlers.Add(handler.Id, handler);
        }