dart - Flutter - JSON 和时间序列图表

Question

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。一个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),
    ];

有完整的简单代码供引用。请随意发表评论。谢谢。

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,
          ],
        ),
      ),
    );
  }
}

Answer 1

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，您需要构建数据。

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。)