How fetch data from Internet in this example? - dart

Question

This is one official example of simple BarChart for Flutter app - https://google.github.io/charts/flutter/example/bar_charts/simple
I wood like fetch data from Internet for this chart. Here is the data - http://skazkimal.ru/hr-metrics/headcount.json
My code is not work, because method _createSampleData is async:
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:hr_metrics/FetchChartData.dart';
import 'package:http/http.dart' as http;
class SalaryView extends StatelessWidget{
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('FFFFFFFFF'),
),
body: Padding(
padding: const EdgeInsets.all(10.0),
child: new SalaryChart.withSampleData(),
),
);
}
}
class SalaryChart extends StatelessWidget{
final List<charts.Series> seriesList;
final bool animate;
SalaryChart(this.seriesList, {this.animate});
/// Creates a [BarChart] with sample data and no transition.
factory SalaryChart.withSampleData() {
return new SalaryChart(
_createSampleData(),
// Disable animations for image tests.
animate: true,
);
}
#override
Widget build(BuildContext context) {
// This is just a simple bar chart with optional property
// [defaultInteractions] set to true to include the default
// interactions/behaviors when building the chart.
// This includes bar highlighting.
//
// Note: defaultInteractions defaults to true.
//
// [defaultInteractions] can be set to false to avoid the default
// interactions.
return new charts.BarChart(
seriesList,
animate: animate,
defaultInteractions: true,
barRendererDecorator: new charts.BarLabelDecorator<String>(),
vertical: false,
);
}
/// Create one series with sample hard coded data.
static Future<List<charts.Series<ChartData, String>>> _createSampleData() async {
final data = await fetchData(http.Client());
return [
new charts.Series<ChartData, String>(
id: 'Numbers',
domainFn: (ChartData series, _) => series.period,
measureFn: (ChartData series, _) => series.count,
data: data,
labelAccessorFn: (ChartData series, _) => '${series.count.toString()}'
)
];
}
}
/// Sample ordinal data type.
class OrdinalSalary {
final String year;
final int salary;
OrdinalSalary(this.year, this.salary);
}

Answer 1

You cannot use an async method in a constructor like that. Instead, you should create an async method like so:
static Future<SalaryChart> withSampleData() => _createSampleData().then((data) => SalaryChart(data, animate: true));
Which you would use elsewhere:
SalaryChart myChart = await SalaryChart.withSampleData();