Flutter - JSON and Time Series Charts

Question

I am trying to display some data in a time-series chart, I found an example \"https://google.github.io/charts/flutter/example/time_series_charts/simple.html\" but the data i

Answer 1

@Richard Heap, thanks for your prompt reply. According to your advice. I modified the source code as the following.

1. I encountered the NULL pointer of dataJSON. To overcome this problem, applied some exceptional handling.
2. When draw the chart, I encountered that the data(dataJSON) was delayed, I added a dummy list to handle the exception.

Please feel free to comment.

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';

// JSON format
// {"Response":"Success","Type":100,"Aggregated":false,"Data":
// [{"time":1279324800,"close":0.04951,"high":0.04951,"low":0.04951,"open":0.04951,"volumefrom":20,"volumeto":0.9902},

/// Time-series data type.
class TimeSeriesPrice {
  final DateTime time;
  final double price;
  TimeSeriesPrice(this.time, this.price);
}

class ItemDetailsPage extends StatefulWidget {
  @override
  _ItemDetailsPageState createState() => new _ItemDetailsPageState();
}

class _ItemDetailsPageState extends State {
  String url =
      "https://min-api.cryptocompare.com/data/histoday?fsym=BTC&tsym=USD&limit=1&aggregate=1&allData=true";

  List dataJSON;

  Future getCoinsTimeSeries() async {
    var response = await http
        .get(Uri.encodeFull(url), headers: {"Accept": "application/json"});

    if (this.mounted) {
      this.setState(() {
        var extractdata = json.decode(response.body);
        dataJSON = extractdata["Data"];
      });
    }
  }

  @override
  void initState() {
    this.getCoinsTimeSeries();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(title: new Text("Details")),
      body: chartWidget(),
    );
  }

  Widget chartWidget() {
    List tsdata = [];
    if (dataJSON != null) {
      for (Map m in dataJSON) {
        try {
          tsdata.add(new TimeSeriesPrice(
              new DateTime.fromMillisecondsSinceEpoch(m['time'] * 1000, isUtc: true), m['close']+.0));
        } catch (e) {
          print(e.toString());
        }
      }
    } else {
      // Dummy list to prevent dataJSON = NULL
      tsdata.add(new TimeSeriesPrice(new DateTime.now(), 0.0));
    }

    var series = [
      new charts.Series(
        id: 'Price',
        colorFn: (_, __) => charts.MaterialPalette.blue.shadeDefault,
        domainFn: (TimeSeriesPrice coinsPrice, _) => coinsPrice.time,
        measureFn: (TimeSeriesPrice coinsPrice, _) => coinsPrice.price,
        data: tsdata,
      ),
    ];

    var chart = new charts.TimeSeriesChart(
      series,
      animate: true,
    );

    return new Container(
      child: new Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          new Padding(
            padding: new EdgeInsets.all(32.0),
            child: new SizedBox(
              height: 200.0,
              child: chart,
            ),
          ),
        ],
      ),
    );
  }
}