onData method
Remove series IDs from the currently hidden list if those series have been removed from the chart data. The goal is to allow any metric that is removed from a chart, and later re-added to it, to be visible to the user.
Implementation
@override
void onData(List<MutableSeries<D>> seriesList) {
// If a series was removed from the chart, remove it from our current list
// of hidden series.
final seriesIds = seriesList.map((series) => series.id);
_hiddenSeriesList.removeWhere((id) => !seriesIds.contains(id));
}