_TypeError（类型'Null'不是'String'类型的子类型）Flutter-jsonserialisable

Question

我使用 json_serializable 包将数据转换为 JSON 格式作为 Dart 类，但出现错误，这是反序列化的类代码

import 'package:json_annotation/json_annotation.dart';

part 'country.g.dart';

@JsonSerializable()
class Country {
  final String name;
  final List<String> topLevelDomain;
  final String alpha2Code;
  final String alpha3Code;
  final List<String> callingCodes;
  final String capital;
  final List<String> altSpellings;
  final String region;
  final String continent;
  final int population;
  final List<int> latlng;
  final String demonym;
  final int area;
  final double gini;
  final List<String> timezones;
  final List<String> borders;
  final String nativeName;
  final String numericCode;
  final List<Currencies> currencies;
  final List<Languages> languages;
  final Translations translations;
  final List<String> flags;
  final List<RegionalBlocs> regionalBlocs;
  final String cioc;
  final bool independent;

  Country(
      {required this.name,
      required this.topLevelDomain,
      required this.alpha2Code,
      required this.alpha3Code,
      required this.callingCodes,
      required this.capital,
      required this.altSpellings,
      required this.region,
      required this.continent,
      required this.population,
      required this.latlng,
      required this.demonym,
      required this.area,
      required this.gini,
      required this.timezones,
      required this.borders,
      required this.nativeName,
      required this.numericCode,
      required this.currencies,
      required this.languages,
      required this.translations,
      required this.flags,
      required this.regionalBlocs,
      required this.cioc,
      required this.independent});

  factory Country.fromJson(Map<String, dynamic> json) =>
      _$CountryFromJson(json);

  Map<String, dynamic> toJson() => _$CountryToJson(this);
}

@JsonSerializable()
class Currencies {
  final String code;
  final String name;
  final String symbol;

  Currencies({
    required this.code,
    required this.name,
    required this.symbol,
  });

  factory Currencies.fromJson(Map<String, dynamic> json) =>
      _$CurrenciesFromJson(json);

  Map<String, dynamic> toJson() => _$CurrenciesToJson(this);
}

@JsonSerializable()
class Languages {
  final String iso6391;
  final String iso6392;
  final String name;
  final String nativeName;

  Languages({
    required this.iso6391,
    required this.iso6392,
    required this.name,
    required this.nativeName,
  });

  factory Languages.fromJson(Map<String, dynamic> json) =>
      _$LanguagesFromJson(json);

  Map<String, dynamic> toJson() => _$LanguagesToJson(this);
}

@JsonSerializable()
class Translations {
  final String br;
  final String pt;
  final String nl;
  final String hr;
  final String fa;
  final String de;
  final String es;
  final String fr;
  final String ja;
  final String it;
  final String hu;

  Translations(
      {required this.br,
      required this.pt,
      required this.nl,
      required this.hr,
      required this.fa,
      required this.de,
      required this.es,
      required this.fr,
      required this.ja,
      required this.it,
      required this.hu});

  factory Translations.fromJson(Map<String, dynamic> json) =>
      _$TranslationsFromJson(json);

  Map<String, dynamic> toJson() => _$TranslationsToJson(this);
}

@JsonSerializable()
class RegionalBlocs {
  final String acronym;
  final String name;
  final List<String> otherNames;
  final List<String> otherAcronyms;

  RegionalBlocs({
    required this.acronym,
    required this.name,
    required this.otherNames,
    required this.otherAcronyms,
  });

  factory RegionalBlocs.fromJson(Map<String, dynamic> json) =>
      _$RegionalBlocsFromJson(json);

  Map<String, dynamic> toJson() => _$RegionalBlocsToJson(this);
}

这是包生成的文件。

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'country.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Country _$CountryFromJson(Map<String, dynamic> json) => Country(
      name: json['name'] as String,
      topLevelDomain: (json['topLevelDomain'] as List<dynamic>)
          .map((e) => e as String)
          .toList(),
      alpha2Code: json['alpha2Code'] as String,
      alpha3Code: json['alpha3Code'] as String,
      callingCodes: (json['callingCodes'] as List<dynamic>)
          .map((e) => e as String)
          .toList(),
      capital: json['capital'] as String,
      altSpellings: (json['altSpellings'] as List<dynamic>)
          .map((e) => e as String)
          .toList(),
      region: json['region'] as String,

这是引发异常的行

      continent: json['continent'] as String,
//...

      population: json['population'] as int,
      latlng: (json['latlng'] as List<dynamic>).map((e) => e as int).toList(),
      demonym: json['demonym'] as String,
      area: json['area'] as int,
      gini: (json['gini'] as num).toDouble(),
      timezones:
          (json['timezones'] as List<dynamic>).map((e) => e as String).toList(),
      borders:
          (json['borders'] as List<dynamic>).map((e) => e as String).toList(),
      nativeName: json['nativeName'] as String,
      numericCode: json['numericCode'] as String,
      currencies: (json['currencies'] as List<dynamic>)
          .map((e) => Currencies.fromJson(e as Map<String, dynamic>))
          .toList(),
      languages: (json['languages'] as List<dynamic>)
          .map((e) => Languages.fromJson(e as Map<String, dynamic>))
          .toList(),
      translations:
          Translations.fromJson(json['translations'] as Map<String, dynamic>),
      flags: (json['flags'] as List<dynamic>).map((e) => e as String).toList(),
      regionalBlocs: (json['regionalBlocs'] as List<dynamic>)
          .map((e) => RegionalBlocs.fromJson(e as Map<String, dynamic>))
          .toList(),
      cioc: json['cioc'] as String,
      independent: json['independent'] as bool,
    );

Map<String, dynamic> _$CountryToJson(Country instance) => <String, dynamic>{
      'name': instance.name,
      'topLevelDomain': instance.topLevelDomain,
      'alpha2Code': instance.alpha2Code,
      'alpha3Code': instance.alpha3Code,
      'callingCodes': instance.callingCodes,
      'capital': instance.capital,
      'altSpellings': instance.altSpellings,
      'region': instance.region,
      'continent': instance.continent,
      'population': instance.population,
      'latlng': instance.latlng,
      'demonym': instance.demonym,
      'area': instance.area,
      'gini': instance.gini,
      'timezones': instance.timezones,
      'borders': instance.borders,
      'nativeName': instance.nativeName,
      'numericCode': instance.numericCode,
      'currencies': instance.currencies,
      'languages': instance.languages,
      'translations': instance.translations,
      'flags': instance.flags,
      'regionalBlocs': instance.regionalBlocs,
      'cioc': instance.cioc,
      'independent': instance.independent,
    };

Currencies _$CurrenciesFromJson(Map<String, dynamic> json) => Currencies(
      code: json['code'] as String,
      name: json['name'] as String,
      symbol: json['symbol'] as String,
    );

Map<String, dynamic> _$CurrenciesToJson(Currencies instance) =>
    <String, dynamic>{
      'code': instance.code,
      'name': instance.name,
      'symbol': instance.symbol,
    };

Languages _$LanguagesFromJson(Map<String, dynamic> json) => Languages(
      iso6391: json['iso6391'] as String,
      iso6392: json['iso6392'] as String,
      name: json['name'] as String,
      nativeName: json['nativeName'] as String,
    );

Map<String, dynamic> _$LanguagesToJson(Languages instance) => <String, dynamic>{
      'iso6391': instance.iso6391,
      'iso6392': instance.iso6392,
      'name': instance.name,
      'nativeName': instance.nativeName,
    };

Translations _$TranslationsFromJson(Map<String, dynamic> json) => Translations(
      br: json['br'] as String,
      pt: json['pt'] as String,
      nl: json['nl'] as String,
      hr: json['hr'] as String,
      fa: json['fa'] as String,
      de: json['de'] as String,
      es: json['es'] as String,
      fr: json['fr'] as String,
      ja: json['ja'] as String,
      it: json['it'] as String,
      hu: json['hu'] as String,
    );

Map<String, dynamic> _$TranslationsToJson(Translations instance) =>
    <String, dynamic>{
      'br': instance.br,
      'pt': instance.pt,
      'nl': instance.nl,
      'hr': instance.hr,
      'fa': instance.fa,
      'de': instance.de,
      'es': instance.es,
      'fr': instance.fr,
      'ja': instance.ja,
      'it': instance.it,
      'hu': instance.hu,
    };

RegionalBlocs _$RegionalBlocsFromJson(Map<String, dynamic> json) =>
    RegionalBlocs(
      acronym: json['acronym'] as String,
      name: json['name'] as String,
      otherNames: (json['otherNames'] as List<dynamic>)
          .map((e) => e as String)
          .toList(),
      otherAcronyms: (json['otherAcronyms'] as List<dynamic>)
          .map((e) => e as String)
          .toList(),
    );

Map<String, dynamic> _$RegionalBlocsToJson(RegionalBlocs instance) =>
    <String, dynamic>{
      'acronym': instance.acronym,
      'name': instance.name,
      'otherNames': instance.otherNames,
      'otherAcronyms': instance.otherAcronyms,
    };

请帮助我，我开始 Flutter 和 Dart 已经两个月了，这个问题完全阻止了我，提前谢谢你。

Answer 1

将continent: json['continent'] as String更改为

continent: json['continent']??""

如果您希望将其从生成器转换，请将大陆的值更改为 null 并生成。 这应该导致它的类型是动态的