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;
}