flutter - 'List'类型不是 'List'类型的子类型

Question

我是Flutter的初学者。我想创建将数据显示为list，piechart和barchart的TabBarView。当我开始编码时，一切都很好。为了查看它是否正常工作，我在选项卡上附加了不同的颜色。首先，我添加了工作正常的数据列表。但是，当我尝试添加PieChart时，在Title出现此错误。我该怎么办 ？

import 'package:flutter/material.dart';
import 'package:tezversion1/models/Car.dart';
import 'package:charts_flutter/flutter.dart' as charts;

class ComplainPage extends StatefulWidget {
  YearList year;
  ComplainPage(this.year);
  @override
  State<StatefulWidget> createState() => _ComplainPageState(year);
}

class _ComplainPageState extends State {
  YearList year;
  _ComplainPageState(this.year);

  List<charts.Series<Complain, String>> _seriesPieData;

  _generateData() {
    var pieData = [];

    for (var i = 0; i < year.errorList.length; i += 2) {
      pieData.add(new Complain(year.errorList.keys.elementAt(i),
          year.errorList.values.elementAt(i)));

      _seriesPieData.add(
        charts.Series(
          data: pieData,
          domainFn: (Complain complain, _) => complain.complain,
          measureFn: (Complain complain, _) => complain.complainCount,
          id: 'Pie Chart of Complain Counts',
          labelAccessorFn: (Complain row, _) => '${row.complainCount}',
        ),
      );
    }
  }

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

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: 3,
      child: Scaffold(
        appBar: AppBar(
          backgroundColor: Color(0xFF151026),
          title: Text('Complains of year ${year.year}'),
          bottom: TabBar(
            tabs: <Widget>[
              Tab(
                text: 'Data',
              ),
              Tab(
                text: 'Pie Chart',
              ),
              Tab(
                text: 'Bar Chart',
              ),
            ],
          ),
        ),
        body: TabBarView(children: <Widget>[
          Card(
              color: Colors.white,
              elevation: 2.0,
              child: ListView.builder(
                  itemCount: year.errorList.length,
                  itemBuilder: (context, index) {
                    Map<String, double> errorList = year.errorList;
                    return Column(
                      children: <Widget>[
                        new ListTile(
                          title: Text(
                              capitalizer(errorList.keys.elementAt(index))),
                          subtitle: Text(decider(
                              errorList.keys.elementAt(index),
                              errorList.values.elementAt(index).toString())),
                        ),
                        new Divider(
                          color: Colors.black,
                          height: 5,
                          thickness: 1,
                          indent: 5,
                          endIndent: 5,
                        ),
                      ],
                    );
                  })),
          Container(
            child: Center(
              child: Column(
                children: <Widget>[
                  Text(
                    'Pie Chart of Complain Counts for This Car',
                    style:
                        TextStyle(fontSize: 24.0, fontWeight: FontWeight.bold),
                  ),
                  SizedBox(
                    height: 10.0,
                  ),
                  Expanded(
                      child: charts.PieChart(_seriesPieData,
                          animate: true,
                          animationDuration: Duration(seconds: 5),
                          behaviors: [
                            new charts.DatumLegend(
                              outsideJustification:
                                  charts.OutsideJustification.endDrawArea,
                              horizontalFirst: false,
                              desiredMaxRows: 2,
                              cellPadding:
                                  new EdgeInsets.only(right: 4.0, bottom: 4.0),
                              entryTextStyle: charts.TextStyleSpec(
                                  color: charts
                                      .MaterialPalette.purple.shadeDefault,
                                  fontFamily: 'Georgia',
                                  fontSize: 11),
                            )
                          ],
                          defaultRenderer: new charts.ArcRendererConfig(
                              arcWidth: 100,
                              arcRendererDecorators: [
                                new charts.ArcLabelDecorator(
                                    labelPosition:
                                        charts.ArcLabelPosition.inside)
                              ]))),
                ],
              ),
            ),
          ),
          Container(
            color: Colors.purple,
          )
        ]),
      ),
    );
  }

  String capitalizer(String value) {
    String capitalizedString = value[0].toUpperCase() + value.substring(1);
    return capitalizedString;
  }

  String decider(String name, String value) {
    if (name.startsWith("Average")) {
      return "Average Milage : " + value + " miles";
    } else {
      return "Complain Count : " + value;
    }
  }
}

class Complain {
  String complain;
  double complainCount;

  Complain(this.complain, this.complainCount);
}

Answer 1

我认为你需要改变

var pieData = [];

至

List<Complain> pieData = [];

因为您创建的是 _seriesPieData，它是char.Series的列表，其中 Complain的列表为数据，但是 pieData是动态的，如错误中所述。

如果它不起作用，请提供stacktrace以及触发此错误的行。