setData method
Implementation
@override
void setData(int index, ChartSegment segment) {
  super.setData(index, segment);
  final num bottom = xAxis!.crossesAt ?? max(yAxis!.visibleRange!.minimum, 0);
  segment as StepAreaSegment<T, D>
    ..series = this
    .._xValues = xValues
    .._yValues = yValues
    .._bottom = bottom;
}