json_serializable:A sample that serializes and deserializes inherited classes.

dart_sample1.dart

import 'dart:convert';
import 'package:json_annotation/json_annotation.dart';

part 'dart_sample1.g.dart';

@JsonSerializable()
class ClassA {
  static const classType = "type";
  final String title;
  final int count;

  ClassA({required this.title, required this.count});

  void output() {
    print("title = $title, count = $count");
  }

  static Map<String, ClassA Function(Map<String, dynamic>)> factorymap = {};

  factory ClassA.fromJson(Map<String, dynamic> json) {
    if (!json.containsKey(classType)) {
      return _$ClassAFromJson(json);
    } else {
      return factorymap[json[classType] as String]!(json);
    }
  }

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

@JsonSerializable()
class ClassB extends ClassA {
  static const className = "classb";

  final double value;
  @override
  void output() {
    print("title = $title, count = $count value = $value");
  }

  ClassB({required title, required count, required this.value})
      : super(title: title, count: count);

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

  @override
  Map<String, dynamic> toJson() {
    final result = _$ClassBToJson(this);
    result[ClassA.classType] = className;
    return result;
  }

  static void register() {
    ClassA.factorymap[className] = ClassB.fromJson;
  }
}

@JsonSerializable()
class ListClass {
  final List<ClassA> list;

  ListClass({required this.list});

  factory ListClass.create() => ListClass(list: <ClassA>[]);

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

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

  void output() {
    for (final i in list) {
      i.output();
    }
  }
}

/// JSONのシリアライズ・デシリアライズ本体。
void jsonProcess() {
  ClassB.register();
  final list = ListClass.create();
  list.list.add(ClassA(title: "hoge", count: 5));
  list.list.add(ClassA(title: "hage", count: 5));
  list.list.add(ClassB(title: "fuga", count: 3, value: 2.0));

  print("list");
  list.output();

  var jstr = json.encode(list.toJson());

  print(jstr);

  final result = ListClass.fromJson(json.decode(jstr));
  print("result");
  result.output();
}