public void Add(KeyValuePair <int, XLRow> item)
        {
            if (item.Key > MaxRowUsed)
            {
                MaxRowUsed = item.Key;
            }

            if (Deleted.ContainsKey(item.Key))
            {
                Deleted.Remove(item.Key);
            }

            _dictionary.Add(item.Key, item.Value);
        }