dart - Flutter - JSON 和时间序列图表
问题描述
我试图在时间序列图表中显示一些数据,我找到了一个示例“ https://google.github.io/charts/flutter/example/time_series_charts/simple.html ”,但数据不是来自互联网的请求。问题是如何将 JSON 数据应用到时间序列数据中。时序数据的代码如下:
final data = [
// How to apply the JSON data in TimeSeriesSales ?
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),
];
有一个完整的简单代码供参考。请随意发表评论。谢谢你。
import 'dart:async';
import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:charts_flutter/flutter.dart' as charts;
import 'package:flutter/material.dart';
/// Sample time series data type.
class TimeSeriesSales {
final DateTime time;
final int sales;
TimeSeriesSales(this.time, this.sales);
}
class ItemDetailsPage extends StatefulWidget {
@override
_ItemDetailsPageState createState() => new _ItemDetailsPageState();
}
class _ItemDetailsPageState extends State<ItemDetailsPage> {
String url =
"https://min-api.cryptocompare.com/data/histoday?fsym=BTC&tsym=USD&limit=1&aggregate=1&allData=true";
List dataJSON;
Future<String> getCoinsTimeSeries() async {
var response = await http
.get(Uri.encodeFull(url), headers: {"Accept": "application/json"});
setState(() {
var extractdata = json.decode(response.body);
dataJSON = extractdata["Data"];
});
}
@override
void initState() {
this.getCoinsTimeSeries();
}
@override
Widget build(BuildContext context) {
final data = [
// How to apply the JSON data in TimeSeriesSales ?
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),
];
var series = [
new charts.Series<TimeSeriesSales, DateTime>(
id: 'Sales',
colorFn: (_, __) => charts.MaterialPalette.blue.shadeDefault,
domainFn: (TimeSeriesSales sales, _) => sales.time,
measureFn: (TimeSeriesSales sales, _) => sales.sales,
data: data,
)
];
var chart = new charts.TimeSeriesChart(
series,
animate: true,
);
var chartWidget = new Padding(
padding: new EdgeInsets.all(32.0),
child: new SizedBox(
height: 200.0,
child: chart,
),
);
return Scaffold(
appBar: new AppBar(title: new Text("Details")),
body: new Center(
child: new Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
new Text(
'You have pushed the button this many times:',
),
chartWidget,
],
),
),
);
}
}
解决方案
首先要做的是重构TimeSeriesSales
,使其在您的应用程序中有意义,例如:
class TimeSeriesPrice {
final DateTime time;
final double price;
TimeSeriesSales(this.time, this.price);
}
接下来,您需要构建data
.
List<TimeSeriesPrice> data = [];
// populate data with a list of dates and prices from the json
for (Map m in dataJSON) {
data.add(TimeSeriesPrice(m['date'], m['price']);
}
var series = ...
你没有给出json格式的例子,所以这是一个猜测。(您可能必须将 json 字符串日期解析为 Dart DateTime。)
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