Flutter abstract class with factory methods - flutter

Question

I am new to working with dart/flutter!
Tell me pls how to correctly implement an abstract class in which a factory method is needed
I have a large number of models with the same methods (factory Model.fromJsom, listFromJson)! I want to make an interface for such models, but I don’t understand how to make a factory method and a static in abstract class
Examples
class Post extends Equatable {
Post({
required this.id,
required this.title,
});
final int id;
final String title;
#override
List<Object> get props => [
id,
title,
];
factory Post.fromJson(dynamic json) {
return Post(
id: json['id'] as int,
title: json['name'] as String,
);
}
Map<String, dynamic> toJson() {
return {
'id': id,
'title': title,
};
}
static List<Post> listFromJson(List<dynamic> json) {
return json.map((value) => Post.fromJson(value)).toList();
}
#override
String toString() {
return '''Post { id: $id, title: $title }''';
}
}

Answer 1

I find it's always a headache to work with JSON array directly. The solution I find is to wrap the List inside another class, in this case ListPost as follows:
class Post {
final int id;
final String title;
Post({required this.id, required this.title});
factory Post.fromJson(Map<String, dynamic> json) => Post(
id: json['id'] as int,
title: json['title'] as String,
);
Map<String, dynamic> toJson() => <String, dynamic>{
'id': id,
'title': title,
};
}
class ListPost {
final List<Post> list;
ListPost({required this.list});
factory ListPost.fromJson(Map<String, dynamic> json) => ListPost(
list: (json['list'] as List<dynamic>)
.map((e) => Post.fromJson(e as Map<String, dynamic>))
.toList(),
);
Map<String, dynamic> toJson() => <String, dynamic>{
'list': list,
};
}
And the example JSON is like this:
{
"list": [
{"id": 1, "title": "TITLE_1"},
{"id": 2, "title": "TITLE_2"}
]
}
I hope this is workable for you.

Answer 2

You can simply use this website it will convert your json to a dart file and you can easily call the methods .fromJson and .toJson to convert from json to entity and vice versa quicktype website
JSON source
{
"greeting": "Welcome to quicktype!",
"instructions": [
"Type or paste JSON here",
"Or choose a sample above",
"quicktype will generate code in your",
"chosen language to parse the sample data"
]
}
Dart file
import 'dart:convert';
Welcome welcomeFromJson(String str) => Welcome.fromJson(json.decode(str));
String welcomeToJson(Welcome data) => json.encode(data.toJson());
class Welcome {
Welcome({
this.greeting,
this.instructions,
});
String greeting;
List<String> instructions;
factory Welcome.fromJson(Map<String, dynamic> json) => Welcome(
greeting: json["greeting"] == null ? null : json["greeting"],
instructions: json["instructions"] == null ? null : List<String>.from(json["instructions"].map((x) => x)),
);
Map<String, dynamic> toJson() => {
"greeting": greeting == null ? null : greeting,
"instructions": instructions == null ? null : List<dynamic>.from(instructions.map((x) => x)),
};
}