如何在波动图中添加标签？

Question

我想从Json文件中为X和Y轴添加标签。我不知道如何在文件中的图形中添加标签。这是我的Json文件，

    [
  {
    "saleyear": "2015",
    "saleval": "10",
    "salelabel": "first"
  },
  {
    "saleyear": "2016",
    "saleval": "30",
    "salelabel": "second"
  },
  {
    "saleyear": "2017",
    "saleval": "40",
    "salelabel": "third"
  },
  {
    "saleyear": "2018",
    "saleval": "10",
    "salelabel": "fourth"
  }
]

这是我的代码，可以显示来自Json文件的X和Y轴数据，

import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'dart:convert';

class HomePage extends StatefulWidget {
  final Widget child;

  HomePage({Key key, this.child}) : super(key: key);

  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  List<charts.Series<Sales, String>> seriesBarData;

  _generateData() async {
    final load =
        await DefaultAssetBundle.of(context).loadString("asset/data.json");
    var decoded = json.decode(load);
    List<Sales> sales = [];
    for (var item in decoded) {
      sales.add(Sales.fromJson(item));
    }

    seriesBarData.add(charts.Series(
      data: sales,
      domainFn: (Sales sales, _) => sales.saleyear,
      measureFn: (Sales sales, _) => int.parse(sales.saleval),
      //colorFn: (Sales sales, _) => charts.ColorUtil.fromDartColor(Color(int.parse(sales.salelabel))),
      id: 'Performance',
      //labelAccessorFn: (Sales row,_)=>"${row.saleyear}",
    ));
    setState(() {});
  }

  @override
  void initState() {
    super.initState();
    seriesBarData = List<charts.Series<Sales, String>>();
    _generateData();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.cyan,
        title: Text('flutter charts'),
      ),
      body: Column(
        children: [
          Text(
            'Frame per Second',
            style: TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold),
          ),
          SizedBox(
            height: 10.0,
          ),
          if (seriesBarData.length > 0)
            Expanded(
              child: charts.BarChart(
                seriesBarData,
                animate: true,
                animationDuration: Duration(seconds: 5),
                domainAxis: new charts.OrdinalAxisSpec(
                  viewport: new charts.OrdinalViewport('AePS', 9),
                ),





                behaviors: [
                  new charts.ChartTitle('Time,seconds',

                      // titleStyleSpec: chartsCommon.TextStyleSpec(fontSize: 11),
                      titleOutsideJustification:
                          charts.OutsideJustification.middleDrawArea),
                  new charts.ChartTitle('Number of Frames',
                      behaviorPosition: charts.BehaviorPosition.start,
                      // titleStyleSpec: chartsCommon.TextStyleSpec(fontSize: 11),
                      titleOutsideJustification:
                          charts.OutsideJustification.middleDrawArea),
                  new charts.DatumLegend(),

                ],
              ),
            )
          else
            Container(),
        ],
      ),
    );
  }
}

class Sales {
  String saleyear;
  String saleval;
  String salelabel;

  Sales(this.saleyear, this.saleval, this.salelabel);

  Sales.fromJson(Map<String, dynamic> json) {
    saleyear = json['saleyear'];
    saleval = json['saleval'];
    salelabel = json['salelabel'];
  }
}

但是在这里，我使用行为通过硬编码数据在X和Y轴上显示标签，但是我不知道如何设置它，以便可以直接显示本地json文件或后端的数据。