尝试解析JSON文件，但它返回_TypeError (键入'_InternalLinkedHashMap<String，dynamic>‘不是类型’String‘的子类型)

Question

我试图解析一个远程json，但是我总是得到这个错误_TypeError (type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String')，我试图尽可能地简化示例，因为我的模型有点复杂，而且JSON有5000多个单词。

这是我的功能：

Future<void> updateCrypto(String symbol) async {

    Uri url = Uri.https(); // url where I get the json

    try {
      final response = await http.get(url);

      final parsedJson = json.decode(response.body) as Map<String, dynamic>;
      final Cryptocurrency updatedCrypto = Cryptocurrency.fromJson(parsedJson);

    } catch (error) {
      throw (error);
    }
  }

我的模特：

class Cryptocurrency with ChangeNotifier {
  Cryptocurrency({
    required this.id,
    required this.symbol,
    required this.name,
    ...
  });

  late final String id;
  late final String symbol;
  late final String name;
  ...

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

Json示例(因为它是一个5000字的json文件)：

{"id":"bitcoin","symbol":"btc","name":"Bitcoin",   }

Answer 1

我喜欢修改实体和用例，如

import 'dart:convert';

class Cryptocurrency with ChangeNotifier {
  final String id;
  final String symbol;
  final String name;
  Cryptocurrency({
    required this.id,
    required this.symbol,
    required this.name,
  });

  Map<String, dynamic> toMap() {
    final result = <String, dynamic>{};

    result.addAll({'id': id});
    result.addAll({'symbol': symbol});
    result.addAll({'name': name});

    return result;
  }

  factory Cryptocurrency.fromMap(Map<String, dynamic> map) {
    return Cryptocurrency(
      id: map['id'] ?? '',
      symbol: map['symbol'] ?? '',
      name: map['name'] ?? '',
    );
  }

  String toJson() => json.encode(toMap());

  factory Cryptocurrency.fromJson(String source) =>
      Cryptocurrency.fromMap(json.decode(source));
}

用例

     final response = await http.get(Uri.parse(url));
     final parsedJson = json.decode(response.body);

     if (response.statusCode == 200) {
      final data = jsonDecode(response.body);
      final Cryptocurrency updatedCrypto = Cryptocurrency.fromJson(data);