public virtual void Insert(int index, string key, T item)
{
if (_keys.Contains(key))
{
throw new Exception("Key already exist");
}
_keys.Insert(index, key);
_items.Insert(index, item);
if (ItemAdd != null)
{
ItemAdd(this, new KeyedCollectionAddEventArgs(_items[index], index, _keys[index]));
}
if (CollectionChanged != null)
{
CollectionChanged(this, new EventArgs());
}
}