Flutter, Firebase, and Syncfusion charts

class DateLength {
  final Timestamp mydate;
  final double mylength;
  DateLength(this.mydate,this.mylength);

  DateLength.fromMap(Map<dynamic, dynamic> map)
      : assert(map['date'] != null),
        assert(map['length'] != null),
        mydate = map['date'],
        mylength = map['length'];

  @override
  String toString() => "Record<$mydate:$mylength>";

List<ScatterSeries<DateLength, DateTime>> _seriesDateLength;
List<ScatterSeries<DateLength, DateTime>> mydata;
_generateDateLength(mydata) {
  debugPrint("_generateDateLength");
  _seriesDateLength = mydata;//List<ChartSeries<DateLength, Timestamp>>();
  debugPrint("_generateDateLength2");
}

Widget _buildScatterBody(BuildContext context) {
  //debugPrint("CatchesRecords=" + Firestore.instance.collection('catches').snapshots().length.toString());
  return StreamBuilder<QuerySnapshot>(
    stream: Firestore.instance.collection('catches').snapshots(),
    builder: (context, snapshot) {
      if (!snapshot.hasData) {
        debugPrint("nodata");
        return LinearProgressIndicator();
      } else {
        debugPrint("found records " + snapshot.data.documents.length.toString());
        List<DateLength> task = snapshot.data.documents
            .map((documentSnapshot) => DateLength.fromMap(documentSnapshot.data))
            .toList();
        debugPrint("mapped records");
        debugPrint("task.length.tostring:" + task.length.toString());


        return _buildScatterChart(context, _seriesDateLength);
      }
    },
  );
}

Widget _buildScatterChart(BuildContext context, List<ScatterSeries<DateLength, DateTime>> taskdata) {
  mydata = taskdata;
  _generateDateLength(mydata);
  debugPrint("mydata=" + mydata.toString());
  //debugPrint("_seriesDateLength.length=" + _seriesDateLength.length.toString());
  return Padding(
    padding: EdgeInsets.all(8.0),
    child: Container(
      child: Center(
        child: Column(
          children: <Widget>[

            Text(
              'Sample Data',
              style: TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold),
            ),
            SizedBox(
              height: 10.0,
            ),

            Expanded(
              child:
              SfCartesianChart(
                plotAreaBorderWidth: 0,
                title: ChartTitle(text: 'Firebase DateLength'),
                legend: Legend(isVisible: true),
                primaryXAxis: DateTimeAxis(
                  labelIntersectAction: AxisLabelIntersectAction.multipleRows,
                  majorGridLines: MajorGridLines(width: 0),
                ),
                primaryYAxis: NumericAxis(
                    labelFormat: 'Length (in)',
                    axisLine: AxisLine(width: 0),
                    minorTickLines: MinorTickLines(size: 0)),
                tooltipBehavior: TooltipBehavior(enable: true),
                series: _seriesDateLength, 
              ),
            ),
          ],
        ),
      ),
    ),
  );