onAdd method

@override void onAdd(int index, T? item)

Implementation

@override
void onAdd(int index, T? item) {
  var state = key.currentState;
  if (state != null) {
    if (item == null) {
      state.insertItem(index);
    } else {
      int _index = addAt(index, item);
      state.insertItem(_index);
    }
    _listLength++;
  }
}