如何继续在颤振中接收 JSON 数组并解析它？答案

【问题标题】：How to go on about receiving JSON array in flutter and parsing it?如何继续在颤振中接收 JSON 数组并解析它？
【发布时间】：2019-03-05 15:32:58
【问题描述】：

我正在尝试从 Web 服务 URL 获取 JSON 数组并用 JSON 解析它。问题是我正在关注的教程显示接收一个 JSOn obj 并解析它，但我需要知道如何接收 JSON 数组并解析它。下面是我正在处理的代码，我卡住了。

型号

class Fact {
  int id;
  int fact_id;
  String fact;
  String image;
  String reference;

  Fact(this.id, this.fact_id, this.fact, this.image, this.reference);

  Fact.fromJson(Map<String, dynamic> json)
    : id = json['id'],
      fact_id = json['fact_id'],
      fact = json['fact'],
      image = json['image'],
      reference = json['reference'];

    Map<String, dynamic> toJson() =>
    {
      'id' : id,
      'fact_id': fact_id,
      'fact': fact,
      'image': image,
      'reference': reference,
    };
}

我不知道如何为我从网络服务获得的一系列事实编写这个。

事实下载管理器

class FactsManager {
  var constants = Constants();

  fetchFacts() {
    final lastFactId = 0;
    var fetchRequestUrl = constants.fetch_facts_url;

    if (lastFactId == 0) {
      fetchRequestUrl = fetchRequestUrl + "?count=" + constants.firstTimePostCount.toString();
    } else {
      fetchRequestUrl = fetchRequestUrl + "?count=" + constants.firstTimePostCount.toString() + "&last_id=" + lastFactId.toString();
    }
    Future<List<Fact>> fetchPost() async {
      final response = await http.get(fetchRequestUrl);

      if (response.statusCode == 200) {
        return List<Fact>
      }
    }
  }
}

我试图解析的示例数据。

[
    {
        "id": "407",
        "fact": "Monsanto once tried to genetically engineer blue cotton, to produce denim without the use of dyes, reducing the pollution involved in the dyeing process.   ",
        "reference": null,
        "image": "http:\/\/quickfacts.me\/wp-content\/uploads\/2015\/06\/fact492.png",
        "fact_id": "1"
    },
    {
        "id": "560",
        "fact": "You can count from zero to nine hundred ninety-nine without ever having to use the letter \"a\"   ",
        "reference": null,
        "image": "http:\/\/quickfacts.me\/wp-content\/uploads\/2015\/06\/fact04.png",
        "fact_id": "2"
    },
    {
        "id": "564",
        "fact": "In order to keep the project a secret, the British army used the innocuous name \"mobile water carriers\" for a motorized weapons project - which is the reason we call them \"tanks\".   ",
        "reference": null,
        "image": "http:\/\/quickfacts.me\/wp-content\/uploads\/2015\/06\/fact116.png",
        "fact_id": "3"
    },
    {
        "id": "562",
        "fact": "In 2010 the mummified corpse of Sogen Kato, thought to be Tokyo's oldest man, was found in his bedroom by government officials. He had actually died in 1978.   ",
        "reference": null,
        "image": "http:\/\/quickfacts.me\/wp-content\/uploads\/2015\/06\/fact216.png",
        "fact_id": "4"
    },
    {
        "id": "566",
        "fact": "In 1927 the US Supreme Court ruled it constitutional for the government to forcefully sterilize mentally handicapped people   ",
        "reference": null,
        "image": "http:\/\/quickfacts.me\/wp-content\/uploads\/2015\/06\/fact316.png",
        "fact_id": "5"
    }
]

【问题讨论】：

@connexo 好的。我已经编辑了问题并给出了示例数据，那么我该如何解析呢？

标签： json dart flutter

【解决方案1】：

您可以执行以下操作：

String receivedJson = "... Your JSON string ....";
List<dynamic> list = json.decode(receivedJson);
Fact fact = Fact.fromJson(list[0]);

无论如何，您必须在您的 json 字符串和您制作的 Fact 类中考虑以下内容：

在 json 字符串中，id 和 fact_id 是字符串，您将它们视为 int。您要么更改 json 类，要么更改 Fact 类
json 字符串中的某些字符串会产生错误，因为它们有额外的引号，这会使解码器感到困惑。

一个json字符串的作用如下：

String receivedJson = """
[
    {
        "id": 407,
        "fact": "Monsanto once tried to genetically engineer blue cotton, to produce denim without the use of dyes, reducing the pollution involved in the dyeing process.   ",
        "reference": null,
        "image": "http:\/\/quickfacts.me\/wp-content\/uploads\/2015\/06\/fact492.png",
        "fact_id": 1
    }
]
    """;

【讨论】：

【解决方案2】：

使用如下简单数组：

{
  "tags": [
    "dart",
    "flutter",
    "json"
  ]
}

我们可以轻松地将 JSON 解析为 Dart 数组，而无需创建任何类。

import 'dart:convert';

main() {
  String arrayText = '{"tags": ["dart", "flutter", "json"]}';

  var tagsJson = jsonDecode(arrayText)['tags'];
  List<String> tags = tagsJson != null ? List.from(tagsJson) : null;

  print(tags);
}

现在你可以看到打印 Dart Array 的结果了。

[dart, flutter, json]

发件人：Dart/Flutter parse JSON array into List

【讨论】：

【解决方案3】：

轻松

      String arrayText = '[{"name": "dart1","quantity": 12 },{"name": "flutter2","quantity": 25 }]';

      var tagsJson = jsonDecode(arrayText);
      List<dynamic> tags = tagsJson != null ? List.from(tagsJson) : null;

      print(">> " + tags[0]["name"]);
      print(">> " + tags[1]["name"]);
      print(">> " + tags[0]["quantity"].toString());
      print(">> " + tags[1]["quantity"].toString());

输出

2021-04-28 18:55:28.921 22085-22225/com.example.flutter_applicationdemo08 I/flutter: >> dart1
2021-04-28 18:55:28.921 22085-22225/com.example.flutter_applicationdemo08 I/flutter: >> flutter2
2021-04-28 18:55:28.921 22085-22225/com.example.flutter_applicationdemo08 I/flutter: >> 12
2021-04-28 18:55:28.921 22085-22225/com.example.flutter_applicationdemo08 I/flutter: >> 25

【讨论】：