我还是 Flutter 的新手，我一直在尝试在条形图中显示来自 http 请求的一些数据。我找不到任何例子。我希望你们中的一些人可以提供帮助:)

我想用这个 Chart来自在线画廊。我刚刚为我的应用更改了类的名称:

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

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

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

  factory SimpleSeriesLegend.withSampleData() {
    return new SimpleSeriesLegend(
      _createSampleData(),
      // Disable animations for image tests.
      animate: false,
    );
  }

  @override
  Widget build(BuildContext context) {
    return new charts.BarChart(
      seriesList,
      animate: animate,
      barGroupingType: charts.BarGroupingType.grouped,
      // Add the series legend behavior to the chart to turn on series legends.
      // By default the legend will display above the chart.
      behaviors: [new charts.SeriesLegend()],
    );
  }

  /// Create series list with multiple series
  static List<charts.Series<LiveWerkzeuge, String>> _createSampleData() {
    final tool1Data = [
      new LiveWerkzeuge ('WSP1', 5),
      new LiveWerkzeuge ('WSP2', 25),
      new LiveWerkzeuge ('WSP3', 80),
      new LiveWerkzeuge ('WSP4', 75),
      new LiveWerkzeuge ('WSP5', 65),
      new LiveWerkzeuge ('WSP6', 55),
      new LiveWerkzeuge ('WSP7', 70),
      new LiveWerkzeuge ('WSP8', 90),
    ];
    
    return [
      new charts.Series<LiveWerkzeuge, String>(
        id: 'WZG1',
        domainFn: (LiveWerkzeuge wear, _) => wear.wsp,
        measureFn: (LiveWerkzeuge wear, _) => wear.belastung,
        data: tool1Data,
      ),
    ];
  }

}
/// Sample ordinal data type.
class LiveWerkzeuge {
  final String wsp;
  final int belastung;

  LiveWerkzeuge(this.wsp, this.belastung);
}

这是我发现的一个简单代码，用于访问和显示 ListView 中的数据并自动更新。我只是想学习如何做到这一点，它对我有用:

import 'dart:async';
import 'dart:convert';

import 'package:flutter/material.dart';

import 'package:http/http.dart' as http;

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String url = 'http://localhost/werkzeug/public/api/data_tool1';
  List data;
  Timer timer;

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

    setState(() {
      var extractdata = JSON.decode(response.body);
      data = extractdata;
    });
  }

  @override
  void initState() {
    super.initState();
    timer = new Timer.periodic(new Duration(seconds: 2), (Timer timer) async {
      this.makeRequest();
    });
  }

  @override
  void dispose() {
    super.dispose();
    timer.cancel();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        appBar: new AppBar(
          title: new Text('Tool Data'),
        ),
        body: new ListView.builder(
            itemCount: data == null ? 0 : data.length,
            itemBuilder: (BuildContext context, int i) {
              return new ListTile(
                title: new Text('Tool 1 Temperature is : ''${data[i]["temp1"]}' ' and tool 2 is: ''${data[i]["temp2"]}'),
              );
            }
        )
    );
  }
}

现在我想把这两者结合起来。

数据是这样的:

[{"timestamp":"2018-06-29 14:39:18","rpm":0,"rpm_filter":0,"accel":0,"temp1":104,"temp2": 746，“temp3”:134，“temp4”:77，“temp5”:0，“temp6”:0，“temp7”:0，“temp8”:0，“DMS1”:0，“DMS2”:0， “DMS3”:0，“DMS4”:0，“batt”:0，“shock”:0，“shock_accel”:0，“shock_degxy”:0，“shock_degxz”:0，“error”:0，“connection_id” ":0,"Wear1":0,"Wear2":0,"Wear3":0,"Wear4":0,"Wear5":0,"Wear6":0,"Wear7":0,"Wear8": 0,"standzeit1":0,"standzeit2":0,"standzeit3":0,"standzeit4":0,"standzeit5":0,"standzeit6":0,"standzeit7":0,"standzeit8":0} ]

新异常(exception):

I/flutter ( 7654): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 7654): The following RangeError was thrown building MyHomePage(dirty, state: _MyHomePageState#9477b): I/flutter ( 7654): RangeError (index): Invalid value: Only valid value is 0: 1 I/flutter ( 7654): I/flutter ( 7654): When the exception was thrown, this was the stack: I/flutter ( 7654): #0 List.[] (dart:core/runtime/libgrowable_array.dart:141:60) I/flutter ( 7654): #1 _MyHomePageState.createSeries (file:///Users/Eti/AndroidStudioProjects/test_json_app/lib/main.dart:71:35) I/flutter ( 7654): #2 _MyHomePageState.createChart (file:///Users/Eti/AndroidStudioProjects/test_json_app/lib/main.dart:89:7) I/flutter ( 7654): #3 _MyHomePageState.build (file:///Users/Eti/AndroidStudioProjects/test_json_app/lib/main.dart:57:58) I/flutter ( 7654): #4 StatefulElement.build (package:flutter/src/widgets/framework.dart:3743:27) I/flutter ( 7654): #5 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3655:15) I/flutter ( 7654): #6 Element.rebuild (package:flutter/src/widgets/framework.dart:3508:5) I/flutter ( 7654): #7 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2255:33) I/flutter ( 7654): #8 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:626:20) I/flutter ( 7654): #9 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:208:5) I/flutter ( 7654): #10 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15) I/flutter ( 7654): #11 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9) I/flutter ( 7654): #12 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5) I/flutter ( 7654): #13 _invoke (dart:ui/hooks.dart:120:13) I/flutter ( 7654): #14 _drawFrame (dart:ui/hooks.dart:109:3) I/flutter ( 7654): ════════════════════════════════════════════════════════════════════════════════════════════════════ I/flutter ( 7654): Another exception was thrown: RangeError (index): Invalid value: Only valid value is 0: 1 I/flutter ( 7654): Another exception was thrown: RangeError (index): Invalid value: Only valid value is 0: 1

最佳答案

我想你想要的是:

import 'dart:async';
import 'dart:convert';

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

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List data;
  Timer timer;

  makeRequest() async {
    var response = await http.get(
      'http://localhost/werkzeug/public/api/data_tool1',
      headers: {'Accept': 'application/json'},
    );

    setState(() {
      data = json.decode(response.body);
    });
  }

  @override
  void initState() {
    super.initState();
    timer = new Timer.periodic(new Duration(seconds: 2), (t) => makeRequest());
  }

  @override
  void dispose() {
    timer.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Tool Data'),
      ),
      body: data == null ? CircularProgressIndicator() : createChart(),
    );
  }

  charts.Series<LiveWerkzeuge, String> createSeries(String id, int i) {
    return charts.Series<LiveWerkzeuge, String>(
      id: id,
      domainFn: (LiveWerkzeuge wear, _) => wear.wsp,
      measureFn: (LiveWerkzeuge wear, _) => wear.belastung,
      // data is a List<LiveWerkzeuge> - extract the information from data
      // could use i as index - there isn't enough information in the question
      // map from 'data' to the series
      // this is a guess
      data: [
        LiveWerkzeuge('WSP1', data[i]['temp1']),
        LiveWerkzeuge('WSP2', data[i]['temp2']),
        LiveWerkzeuge('WSP3', data[i]['temp3']),
        LiveWerkzeuge('WSP4', data[i]['temp4']),
        LiveWerkzeuge('WSP5', data[i]['temp5']),
        LiveWerkzeuge('WSP6', data[i]['temp6']),
        LiveWerkzeuge('WSP7', data[i]['temp7']),
        LiveWerkzeuge('WSP8', data[i]['temp8']),
      ],
    );
  }

  Widget createChart() {
    // data is a List of Maps
    // each map contains at least temp1 (tool 1) and temp2 (tool 2)
    // what are the groupings?

    List<charts.Series<LiveWerkzeuge, String>> seriesList = [];

    for (int i = 0; i < data.length; i++) {
      String id = 'WZG${i + 1}';
      seriesList.add(createSeries(id, i));
    }

    return new charts.BarChart(
      seriesList,
      barGroupingType: charts.BarGroupingType.grouped,
    );
  }
}

class LiveWerkzeuge {
  final String wsp;
  final int belastung;

  LiveWerkzeuge(this.wsp, this.belastung);
}

关于json - 如何在flutter图表中显示json数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/51349936/