anchor.diff:      _initSelection(TabBarSelection.of(context));
     }
   
  +  void didUpdateConfig(TabBarView oldConfig) {
  +    super.didUpdateConfig(oldConfig);
  +    if (_selection != null && config.children != oldConfig.children)
  +      _updateItemsForSelectedIndex(_selection.index);
  +  }
  +
     void dispose() {
       _selection?.unregisterPerformanceListener(this);
       super.dispose();
  
positive.code:     _selection = selection;
      if (_selection != null) {
        _selection.registerPerformanceListener(this);
        _initItemsAndScrollOffset();
      }
    }
  
  
negative.code:     final int previousSelectedIndex = _selection.previousIndex;
  
      if (selectedIndex < previousSelectedIndex) {
        _updateItemsFromChildren(selectedIndex, previousSelectedIndex);
        _scrollDirection = AnimationDirection.reverse;
      } else {
        _updateItemsFromChildren(previousSelectedIndex, selectedIndex);
        _scrollDirection = AnimationDirection.forward;
      }
  
  