如何在flutter (charts_flutter)的饼图上添加图例？

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

class PieChartWithLegend extends StatelessWidget {
  final List<charts.Series> seriesList;
  final bool animate;

  PieChartWithLegend(this.seriesList, {this.animate});

  @override
  Widget build(BuildContext context) {
    return charts.PieChart(
      seriesList,
      animate: animate,
      behaviors: [
        charts.DatumLegend(
          position: charts.BehaviorPosition.end, // 图例位置
          desiredMaxRows: 2, // 图例最大行数
          horizontalFirst: false, // 图例是否水平排列
          cellPadding: EdgeInsets.only(right: 4.0, bottom: 4.0), // 图例内边距
          entryTextStyle: charts.TextStyleSpec(
            color: charts.MaterialPalette.black, // 图例文字颜色
            fontSize: 11, // 图例文字大小
          ),
        ),
      ],
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: Scaffold(
      appBar: AppBar(title: Text('Pie Chart with Legend')),
      body: Center(
        child: PieChartWithLegend(
          _createSampleData(),
          animate: true,
        ),
      ),
    ),
  ));
}

List<charts.Series<LinearSales, String>> _createSampleData() {
  final data = [
    LinearSales('Category 1', 100),
    LinearSales('Category 2', 200),
    LinearSales('Category 3', 300),
    LinearSales('Category 4', 400),
  ];

  return [
    charts.Series<LinearSales, String>(
      id: 'Sales',
      domainFn: (LinearSales sales, _) => sales.category,
      measureFn: (LinearSales sales, _) => sales.sales,
      data: data,
      labelAccessorFn: (LinearSales sales, _) => '${sales.category}: ${sales.sales}',
    )
  ];
}

class LinearSales {
  final String category;
  final int sales;

  LinearSales(this.category, this.sales);
}