restorable custom class

test_it.dart

class TestIt extends StatefulWidget {
  const TestIt({super.key});

  @override
  State<TestIt> createState() => _TestItState();
}

class _TestItState extends State<TestIt> with RestorationMixin {
  @override
  Widget build(BuildContext context) {
    return Container();
  }

  final v = RestorableCustomClass(MyClass(1, 'my name'));

  @override
  String? get restorationId => 'test_it_restore_id';

  @override
  void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
    registerForRestoration(v, 'cutome_class_key');
  }
}

class MyClass {
  final int id;
  final String name;

  MyClass(this.id, this.name);

  Map<String, dynamic> toMap() {
    return <String, dynamic>{
      'id': id,
      'name': name,
    };
  }

  factory MyClass.fromMap(Map<String, dynamic> map) {
    return MyClass(
      map['id'] as int,
      map['name'] as String,
    );
  }

  String toJson() => json.encode(toMap());

  factory MyClass.fromJson(String source) => MyClass.fromMap(json.decode(source) as Map<String, dynamic>);
}

class RestorableCustomClass extends RestorableValue<MyClass> {
  /// Creates a [RestorableDateTime].
  ///
  /// {@macro flutter.widgets.RestorableNum.constructor}
  RestorableCustomClass(MyClass defaultValue) : _defaultValue = defaultValue;

  final MyClass _defaultValue;

  @override
  MyClass createDefaultValue() => _defaultValue;

  @override
  void didUpdateValue(MyClass? oldValue) {
    assert(debugIsSerializableForRestoration(value.toJson()));
    notifyListeners();
  }

  @override
  MyClass fromPrimitives(Object? data) => MyClass.fromJson(data! as String);

  @override
  Object? toPrimitives() => value.toJson();
}