i_post.dart

class IPost {
  int id;
  int userId;
  String title;
  String body;

  IPost.fromJson(Map<String, dynamic> json) {
    if (json == null) return;
    id = json['id'];
    userId = json['userId'];
    title = json['title'];
    body = json['body'];
  }

  static List<IPost> listFromJson(List<dynamic> json) {
    return json == null ? List<IPost>() : json.map((value) => IPost.fromJson(value)).toList();
  }
}

I think it is a bad practice to write "I" for the class name or even the interface name.
https://github.com/Microsoft/TypeScript/wiki/Coding-guidelines#names

@smhmayboudi Yeah, you're right, but this is Dart and it's popular to do that

Sorry, my mistake.