错误：“预期 1 个位置参数，但找到 0 个”颤振飞镖错误

Question

我正在尝试使用一些图表构建一个应用程序，我从this 示例开始，但它没有启动应用程序的第一部分，所以我尝试添加：

void main() {
  runApp(SimpleTimeSeriesChart());
}

但我明白了

需要 1 个位置参数，但找到了 0 个。 尝试添加缺少的参数。

在第二行。我不知道我做错了什么。谁能帮我解释我做错了什么以及解决方案是什么？信息很清楚，但我不知道我需要添加哪个参数。另外，任何人都可以向我指出有关此特定问题的一些文档吗？谢谢！

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

void main() {
  runApp(SimpleTimeSeriesChart());
}

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

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

  /// Creates a [TimeSeriesChart] with sample data and no transition.
  factory SimpleTimeSeriesChart.withSampleData() {
    return new SimpleTimeSeriesChart(
      _createSampleData(),
      // Disable animations for image tests.
      animate: false,
    );
  }


  @override
  Widget build(BuildContext context) {
    return new charts.TimeSeriesChart(
      seriesList,
      animate: animate,
      // Optionally pass in a [DateTimeFactory] used by the chart. The factory
      // should create the same type of [DateTime] as the data provided. If none
      // specified, the default creates local date time.
      dateTimeFactory: const charts.LocalDateTimeFactory(),
    );
  }

  /// Create one series with sample hard coded data.
  static List < charts.Series < TimeSeriesSales, DateTime >> _createSampleData() {
    final data = [
      new TimeSeriesSales(new DateTime(2017, 9, 19), 5),
      new TimeSeriesSales(new DateTime(2017, 9, 26), 25),
      new TimeSeriesSales(new DateTime(2017, 10, 3), 100),
      new TimeSeriesSales(new DateTime(2017, 10, 10), 75),
    ];

    return [
      new charts.Series < TimeSeriesSales, DateTime > (
        id: 'Sales',
        colorFn: (_, __) => charts.MaterialPalette.blue.shadeDefault,
        domainFn: (TimeSeriesSales sales, _) => sales.time,
        measureFn: (TimeSeriesSales sales, _) => sales.sales,
        data: data,
      )
    ];
  }
}

/// Sample time series data type.
class TimeSeriesSales {
  final DateTime time;
  final int sales;

  TimeSeriesSales(this.time, this.sales);
}

Answer 1

您需要传递第一个参数，因为它不是可选的SimpleTimeSeriesChart(this.seriesList

void main() {
  runApp(SimpleTimeSeriesChart([]));
}

你可以阅读更多关于 Dart 参数here