The argument type 'Id?' can't be assigned to the parameter type 'Id'

Question

Don't know how to resolve it. The two lines show error. It should be resolved to run the code.

I got error on the two lines where type id and names are converted into "id" and "names".

// To parse this JSON data, do
//
//     final welcome = welcomeFromJson(jsonString);

import 'dart:convert';

Welcome welcomeFromJson(String str) => Welcome.fromJson(json.decode(str));

String welcomeToJson(Welcome data) => json.encode(data.toJson());

class Welcome {
  Welcome({
    required this.status,
    required this.totalResults,
    required this.articles,
  });

  String status;
  int totalResults;
  List<Article> articles;

  factory Welcome.fromJson(Map<String, dynamic> json) => Welcome(
        status: json["status"],
        totalResults: json["totalResults"],
        articles: List<Article>.from(
            json["articles"].map((x) => Article.fromJson(x))),
      );

  Map<String, dynamic> toJson() => {
        "status": status,
        "totalResults": totalResults,
        "articles": List<dynamic>.from(articles.map((x) => x.toJson())),
      };
}

class Article {
  Article({
    required this.source,
    required this.author,
    required this.title,
    required this.description,
    required this.url,
    required this.urlToImage,
    required this.publishedAt,
    required this.content,
  });

  Source source;
  String author;
  String title;
  String description;
  String url;
  String urlToImage;
  DateTime publishedAt;
  String content;

  factory Article.fromJson(Map<String, dynamic> json) => Article(
        source: Source.fromJson(json["source"]),
        author: json["author"] == null ? null : json["author"],
        title: json["title"],
        description: json["description"],
        url: json["url"],
        urlToImage: json["urlToImage"],
        publishedAt: DateTime.parse(json["publishedAt"]),
        content: json["content"],
      );

  Map<String, dynamic> toJson() => {
        "source": source.toJson(),
        "author": author == null ? null : author,
        "title": title,
        "description": description,
        "url": url,
        "urlToImage": urlToImage,
        "publishedAt": publishedAt.toIso8601String(),
        "content": content,
      };
}

class Source {
  Source({
    required this.id,
    required this.name,
  });

  Id id;
  Name name;

  factory Source.fromJson(Map<String, dynamic> json) => Source(
        id:  idValues.map[json["id"]],
        name: nameValues.map[json["name"]],
      );

  Map<String, dynamic> toJson() => {
        "id": idValues.reverse[id],
        "name": nameValues.reverse[name],
      };
}

enum Id { THE_WALL_STREET_JOURNAL }

final idValues =
    EnumValues({"the-wall-street-journal": Id.THE_WALL_STREET_JOURNAL});

enum Name { THE_WALL_STREET_JOURNAL }

final nameValues =
    EnumValues({"The Wall Street Journal": Name.THE_WALL_STREET_JOURNAL});

class EnumValues<T> {
  Map<String, T> map;
  late Map<T, String> reverseMap;

  EnumValues(this.map);

  Map<T, String> get reverse {
    if (reverseMap == null) {
      reverseMap = map.map((k, v) => new MapEntry(v, k));
    }
    return reverseMap;
  }
}

I think if we parse them then it can be resolved but I don't know how to parse it.

Answer 1

Change these codes :

  Id id;
  Name name;

to this :

  Id? id;
  Name? name;