将 JSON 解析为 Dart 中的列表

Posted 2023-02-23

【中文标题】将 JSON 解析为 Dart 中的列表

【英文标题】：Parse JSON to List in Dart

【发布时间】：2021-03-22 23:42:29

【问题描述】：

我正在尝试从天气 API 解析一些复杂的 JSON，并将其显示在列表视图中。我使用 quickType 为我生成模型，但似乎无法将数据解析为列表。我相当确定错误的主要部分是我在解析服务文件中的数据时的逻辑，因为来自 API 的数据具有复杂的结构，我不知道如何解析。由于 API 数据，它分为 2 个地图或列表？小时和元。因此有一个额外的课程。请帮帮我。

这是服务/解析文件：

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

class Service 
  static const lat = '-33.7506';
  static const lng = '18.4401';
  static const params =
      'swellDirection,windSpeed,windDirection,wavePeriod,waveHeight,airTemperature';

  static Future<List<Hour>> getConditions() async 
    try 
      final response = await http.get(
          Uri.encodeFull(
              'https://api.stormglass.io/v2/weather/point?lat=$lat&lng=$lng&params=$params&start=2020-12-11&end=2020-12-12'),
          headers: 
            HttpHeaders.authorizationHeader:
                'exampleapi'
          );

      if (200 == response.statusCode) 
        final conditions = conditionsFromJson(response.body);
        print(response.body);
        return conditions.hours;
      
     catch (e) 
      print('Not working');
      return List<Hour>();
    
  

这是我的主文件：

    import 'package:flutter/material.dart';
import 'package:moreapi_practise/weather_model.dart';
import 'Service.dart';

void main() 
  runApp(MyApp());


class MyApp extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'My API Practice'),
    );
  


class MyHomePage extends StatefulWidget 
  MyHomePage(Key key, this.title) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();


class _MyHomePageState extends State<MyHomePage> 
  List<Hour> _conditions;
  bool _loading;

  @override
  void initState() 
    super.initState();
    _loading = true;
    Service.getConditions().then((conditions) 
      _conditions = conditions;
      _loading = false;
    );
  

  @override
  Widget build(BuildContext context) 
    return Scaffold(
      appBar: AppBar(
        title: Text(_loading ? 'Loading...' : 'Conditions'),
      ),
      body: Container(child: ListView.builder(itemBuilder: (context, index) 
        Hour condition = _conditions[index];
        return ListTile(
          title: Text('$condition.airTemperature'),
        );
      )),
    );
  

然后是我的模型：

   // To parse this JSON data, do
//
//     final conditions = conditionsFromJson(jsonString);

import 'dart:convert';

Conditions conditionsFromJson(String str) => Conditions.fromJson(json.decode(str));

String conditionsToJson(Conditions data) => json.encode(data.toJson());

class Conditions 
    Conditions(
        this.hours,
        this.meta,
    );

    List<Hour> hours;
    Meta meta;

    factory Conditions.fromJson(Map<String, dynamic> json) => Conditions(
        hours: List<Hour>.from(json["hours"].map((x) => Hour.fromJson(x))),
        meta: Meta.fromJson(json["meta"]),
    );

    Map<String, dynamic> toJson() => 
        "hours": List<dynamic>.from(hours.map((x) => x.toJson())),
        "meta": meta.toJson(),
    ;


class Hour 
    Hour(
        this.airTemperature,
        this.swellDirection,
        this.time,
        this.waveHeight,
        this.wavePeriod,
        this.windDirection,
        this.windSpeed,
    );

    AirTemperature airTemperature;
    SwellDirection swellDirection;
    DateTime time;
    SwellDirection waveHeight;
    SwellDirection wavePeriod;
    SwellDirection windDirection;
    SwellDirection windSpeed;

    factory Hour.fromJson(Map<String, dynamic> json) => Hour(
        airTemperature: AirTemperature.fromJson(json["airTemperature"]),
        swellDirection: SwellDirection.fromJson(json["swellDirection"]),
        time: DateTime.parse(json["time"]),
        waveHeight: SwellDirection.fromJson(json["waveHeight"]),
        wavePeriod: SwellDirection.fromJson(json["wavePeriod"]),
        windDirection: SwellDirection.fromJson(json["windDirection"]),
        windSpeed: SwellDirection.fromJson(json["windSpeed"]),
    );

    Map<String, dynamic> toJson() => 
        "airTemperature": airTemperature.toJson(),
        "swellDirection": swellDirection.toJson(),
        "time": time.toIso8601String(),
        "waveHeight": waveHeight.toJson(),
        "wavePeriod": wavePeriod.toJson(),
        "windDirection": windDirection.toJson(),
        "windSpeed": windSpeed.toJson(),
    ;


class AirTemperature 
    AirTemperature(
        this.noaa,
        this.sg,
    );

    double noaa;
    double sg;

    factory AirTemperature.fromJson(Map<String, dynamic> json) => AirTemperature(
        noaa: json["noaa"].toDouble(),
        sg: json["sg"].toDouble(),
    );

    Map<String, dynamic> toJson() => 
        "noaa": noaa,
        "sg": sg,
    ;


class SwellDirection 
    SwellDirection(
        this.icon,
        this.meteo,
        this.noaa,
        this.sg,
    );

    double icon;
    double meteo;
    double noaa;
    double sg;

    factory SwellDirection.fromJson(Map<String, dynamic> json) => SwellDirection(
        icon: json["icon"].toDouble(),
        meteo: json["meteo"] == null ? null : json["meteo"].toDouble(),
        noaa: json["noaa"].toDouble(),
        sg: json["sg"].toDouble(),
    );

    Map<String, dynamic> toJson() => 
        "icon": icon,
        "meteo": meteo == null ? null : meteo,
        "noaa": noaa,
        "sg": sg,
    ;


class Meta 
    Meta(
        this.cost,
        this.dailyQuota,
        this.end,
        this.lat,
        this.lng,
        this.params,
        this.requestCount,
        this.start,
    );

    int cost;
    int dailyQuota;
    String end;
    double lat;
    double lng;
    List<String> params;
    int requestCount;
    String start;

    factory Meta.fromJson(Map<String, dynamic> json) => Meta(
        cost: json["cost"],
        dailyQuota: json["dailyQuota"],
        end: json["end"],
        lat: json["lat"].toDouble(),
        lng: json["lng"].toDouble(),
        params: List<String>.from(json["params"].map((x) => x)),
        requestCount: json["requestCount"],
        start: json["start"],
    );

    Map<String, dynamic> toJson() => 
        "cost": cost,
        "dailyQuota": dailyQuota,
        "end": end,
        "lat": lat,
        "lng": lng,
        "params": List<dynamic>.from(params.map((x) => x)),
        "requestCount": requestCount,
        "start": start,
    ;

【参考方案1】：

请检查您的 main.dart 的工作代码。问题是您在 initState 中调用 Service.getConditions。 Service.getConditions 是一个未来，在将数据加载到 ListView 之前，您没有等待 Future 完成。下面的代码将向您展示如何等待 Future 完成然后加载数据的一种方法。在 ListView 中，您显示的是 condition.airTemperature，所以我在那里做了一些更改，现在显示的是 condition.airTemperature.noaa& condition.airTemperature.sg。

import 'package:flutter/material.dart';
import 'package:moreapi_practise/weather_model.dart';
import 'Service.dart';


void main() 
  runApp(MyApp());


class MyApp extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'My API Practice'),
    );
  


class MyHomePage extends StatefulWidget 
  const MyHomePage(Key key, this.title) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();


class _MyHomePageState extends State<MyHomePage> 
  List<Hour> _conditions;
  bool _loading;
  Future myFuture;

  Future _getService() async 
    await Service.getConditions().then((conditions) 
      setState(() 
        _conditions = conditions;
        _loading = false;
      );
    );
  

  @override
  void initState() 
    super.initState();
    _loading = true;
    myFuture = _getService();
  

  @override
  Widget build(BuildContext context) 
    return Scaffold(
      appBar: AppBar(
        title: Text(_loading ? 'Loading...' : 'Conditions'),
      ),
      body: _loading
          ? const Center(
              child: CircularProgressIndicator(),
            )
          : Container(
              child: ListView.builder(
                itemCount: _conditions.length,
                itemBuilder: (context, index) 
                  final Hour condition = _conditions[index];
                  return ListTile(
                    title: Text(
                        '$condition.airTemperature.noaa $condition.airTemperature.sg'),
                  );
                ,
              ),
            ),
    );
  

【讨论】：

哇，这很好用，谢谢，我完全看错了方向，对 dart 和 JSON 来说都是新手，再次感谢！

当我看到一个涉及未来的初学者问题时，我首先检查的是他们是否在等待未来的回归。如果您认为它解决了您的问题，也请支持答案。谢谢。

我下次会知道，而且我的声誉分数太低，无法公开显示：(

【参考方案2】：

试试json['hours’] as List<dynamic>。然后您可以将其传递给解析方法并遍历元素。

List<Hour> hours = parseHourList(json['hours'] as List<dynamic>);

// ...

List<Hour> parseHourList(List<dynamic> jsonList) 
  final List<Hour> list = [];
  for(dynamic element in jsonList) 
    final Hour hour = Hour.fromJson(element as Map<String, dynamic>);
    list.add(hour);
  
  return list;