android - Flutter - 无法解析 json 数组

Question

我想通过这种方式从 rest 网络服务中获取城市列表:

Future<List<City>> fetchCities() async {
  final response =
  await http.get('https://my-url/city',
  headers: {HttpHeaders.acceptHeader: "application/json"});

  if (response.statusCode == 200) {
    // If the call to the server was successful, parse the JSON
    return compute(parseCities, response.body);
  } else {
    // If that call was not successful, throw an error.
    throw Exception('Failed to load cities');
  }
}

然后解析:

List<City> parseCities(String responseBody) {
  final parsed = json.decode(responseBody)['data']['children'].cast<Map<String, dynamic>>();

  return parsed.map<City>((json) => City.fromJson(json['data'])).toList();
}

这是 City 类定义:

class City {
  final String id;
  final String name;

  City({this.id, this.name});

  factory City.fromJson(Map<String, dynamic> json) {
    return City(
      id: json['id'],
      name: json['name'],
    );
  }
}

我的示例 responseBody 是:

[{\"id\":\"599\",\"name\":\"Bia\u0142ystok-dev\",\"location\":{\"long\":\"23.15\",\"lat\":\"53.13\"}}]

(现在，我想省略 location 并且只获取 id 和 name)。我的 json.decode 抛出异常:

type 'String' is not a subtype of type 'int' of 'index'

如何解决？有什么想法吗？

Answer 1

您发布的 json 字符串不包含键 data 或 children 因此要解析该 json，您需要将解析方法更改为以下内容:

List<City> parseCities(String responseBody) {
  final parsed = json.decode(responseBody).cast<Map<String, dynamic>>();

  return parsed.map<City>((json) => City.fromJson(json)).toList();
}

尽管我认为使用 List.from 而不是 .cast 是个好习惯

final parsed = List<Map<String, dynamic>>.from(json.decode(responseBody));