anchor.diff:    int rodIndex,
   );
   
  +/// Default callback for [BarTouchTooltipData.getTooltipItem].
   BarTooltipItem defaultBarTooltipItem(
     BarChartGroupData group,
     int groupIndex,
  
positive.code: /// return null if you don't want to show each item
  /// if user touched the chart, we show a tooltip window on the most top [TouchSpot],
  /// here we get the [BarTooltipItem] from the given [TouchedSpot].
  typedef GetBarTooltipItem = BarTooltipItem Function(
    BarChartGroupData group,
    int groupIndex,
  
negative.code:   }
  }
  
  /// It lerps a [BarChartData] to another [BarChartData] (handles animation for updating values)
  class BarChartDataTween extends Tween<BarChartData> {
    BarChartDataTween({BarChartData begin, BarChartData end}) : super(begin: begin, end: end);
  
  