public void SaveCurrentLettersState(ObservableCollection <string> _letters, bool isUser)
        {
            if (_undoRedoService == null)
            {
                return;
            }

            _undoRedoService.SaveCurrentLettersState(_letters, isUser);

            UndoEnabled = _undoRedoService.UndoEnabled;
            RedoEnabled = _undoRedoService.RedoEnabled;
        }