如何在 Dart\Flutter 中使用我的 JSON 响应

Question

我是 Flutter 的新手，我按照一个小教程从一个简单的 Json 中获取 Json 响应。现在我想从更复杂的 API 中获取我的天气数据。这是我在 Kotlin 中制作的一个项目，效果很好，我只是想看看它在 Flutter 中的情况，但是我在将响应转换为类时遇到了一些问题。 （对不起，如果我的术语不太正确）。

我的json方法是这样的：

  _loadData() async {
    String weatherURL = "https://api.openweathermap.org/data/2.5/onecall?lat=33.441792&lon=-94.037689&exclude=hourly,daily,minutely&appid=myapikey";
    http.Response response = await http.get(weatherURL);
    setState(() {
        final Map<String, dynamic> weathersJSON = json.decode(response.body);
        log(weathersJSON.toString());
        List<dynamic> data = weathersJSON[WeatherData];
        print(data[0]["lat"]);

      for(var weatherJSON in weathersJSON) {
        final weatherData = WeatherData(weatherJSON["lat"], weatherJSON["lon"], weatherJSON["timezone"], weatherJSON["timezone_offset"], weatherJSON["current"]);
        _weatherDatas.add(weatherData);
      }
    });
  }

我的 API 响应类似于：

{"lat":33.44,
 "lon":-94.04,
 "timezone":"America/Chicago",
 "timezone_offset":-18000,
 "current":
    {"dt":1594400068,
    "sunrise":1594379674,
    "sunset":1594430893,
    "temp":303.95,
    "feels_like":306.84,
    "pressure":1018,
    "humidity":62,
    "dew_point":295.83,
    "uvi":11.81,
    "clouds":20,
    "visibility":16093,
    "wind_speed":3.1,
    "wind_deg":260,
    "weather":[
      {"id":801,
      "main":"Clouds",
      "description":"few clouds",
      "icon":"02d"}
      ]
     }
 }

起初我想做一些简单的事情，比如'final weathersJSON = json.decode(response.body);'，但我收到了这个错误

未处理的异常：类型“_InternalLinkedHashMap”不是类型“Iterable”的子类型

所以我根据另一个堆栈问题添加了地图，因为它显然有助于 Json 末尾的天气列表位，并且错误消失了。

但是现在我有点卡住了。我想将所有这些 API 信息添加到一个类中，以便在应用程序的其他地方使用。我制作了一个名为 _weatherDatas 的 WeatherData 类型列表。我正在处理的最新错误是

未处理的异常：NoSuchMethodError：在 null 上调用了方法“[]”。

我非常感谢您的任何建议。

这也是我的数据类：

class WeatherData {
  final double lat;
  final double lon;
  final String timezone;
  final int timezone_offset;
  final Current current;

  WeatherData(this.lat, this.lon, this.timezone, this.timezone_offset, this.current);
}

class Weather {
  final int id;
  final String main;
  final String description;
  final String icon;

  Weather(this.id, this.main, this.description, this.icon);
}

class Current {
  final int dt;
  final int sunrise;
  final int sunset;
  final double temp;
  final double feels_like;
  final int pressure;
  final int humidity;
  final double dew_point;
  final double uvi;
  final int clouds;
  final int visibility;
  final double wind_speed;
  final int wind_deg;
  final List<Weather> weather;

  Current(this.dt, this.sunrise, this.sunset, this.temp, this.feels_like, this.pressure, this.humidity,
      this.dew_point, this.uvi, this.clouds, this.visibility, this.wind_speed, this.wind_deg, this.weather);
}

干杯：D

Answer 1

对于你需要这样做的列表

    class Current {
  final int dt;
  final int sunrise;
  final int sunset;
  final double temp;
  final double feels_like;
  final int pressure;
  final int humidity;
  final double dew_point;
  final double uvi;
  final int clouds;
  final int visibility;
  final double wind_speed;
  final int wind_deg;
  final List<Weather> weather;

  Current(
      this.dt,
      this.sunrise,
      this.sunset,
      this.temp,
      this.feels_like,
      this.pressure,
      this.humidity,
      this.dew_point,
      this.uvi,
      this.clouds,
      this.visibility,
      this.wind_speed,
      this.wind_deg,
      this.weather);

  Current.parseJson(Map<String, dynamic> json) {
    this.dt = json['dt'];
    ...
    //for parsing weather list
    if (json['weather'] != null) {
        var weatherJson = json['weather'] as List<dynamic>;
        weather = weatherJson
            .map((tempJson) => Weather.parseJson(tempJson)) //in weather class you need to write  parseJson
            .toList();
      }
  }
}

Answer 2

在你的模型中

 import 'package:recrearte/model/user.dart';
    class WeatherData {
final double lat;

  final double lon;
  final String timezone;
  final int timezone_offset;
  final Current current;

  WeatherData(
      {this.lat,
      this.lon,
      this.timezone,
      this.timezone_offset,
      this.current,
     });

  factory WeatherData.fromJson(Map<String, dynamic> json) {
    return new WeatherData(
        lat: json["lat"],
        current: json.containsKey('current') ? User.fromJson(json['current']) : null,
        timezone_offset: json["timezone_offset"] ?? 0,
        timezone: json["timezone"] ?? "",
        lon: json["lon"] ?? "",
        );
  }

  Map<String, dynamic> toJson() => {
        "lat": lat ?? "",
        "current": this.current != null ? this.current.toJson() : null,
        "timezone_offset": timezone_offset ?? 0,
        "timezone": timezone ?? "",
        "lon": lon ?? "",
      };
}

服务中

_loadData() async {
    String weatherURL = "https://api.openweathermap.org/data/2.5/onecall?lat=33.441792&lon=-94.037689&exclude=hourly,daily,minutely&appid=myapikey";
    http.Response response = await http.get(weatherURL);
    setState(() {

        var json2 = json.decode(response.body);
        return decode(json2);
    });
  }


  WeatherData decode(dynamic element) {
  return WeatherData.fromJson(element);
}