How to serialize private fields in json-serializable? - flutter

Question

Minimal reproducible code:
#JsonSerializable()
class A {
final int _x;
A(int x) : _x = x;
factory A.fromJson(Map<String, dynamic> json) => _$AFromJson(json);
}
Note:
I don't want to make my private field _x public or define a public x getter.

Answer 1

This PR addresses what you want:
https://github.com/google/json_serializable.dart/pull/1256/files#diff-0acaf4c472e452d1e5d215a15fcd2266ccd02ab6abdfac0080c2fca845eb9096
You will be able to explicitly set includeFromJson and includeToJson on the private fields you want to include.
Example:
class X {
#JsonKey(includeFromJson: true, includeToJson: true)
int _includeMeToTheJsonParsing;
}
It was merged November 30th. Latest package version is v6.5.4, released at October 25th. So you will need to wait a little bit if you want the official release. Otherwise, you can point directly to the latest commit if you need it ASAP.

Answer 2

If you don't want to make your private field public or define a public getter, you can still use a serialization library like json_serializable or built_value to serialize and deserialize the class, but you will need to define a custom toJson method that manually serializes the private field. Here's an example of using json_serializable with a custom toJson method:
import 'package:json_annotation/json_annotation.dart';
part 'my_class.g.dart';
#JsonSerializable()
class MyClass {
final int _x;
MyClass(this._x);
Map<String, dynamic> toJson() => {
'x': _x,
};
factory MyClass.fromJson(Map<String, dynamic> json) => MyClass(json['x'] as int);
}
You can then use the fromJson and toJson methods to serialize and deserialize your class:
import 'dart:convert';
void main() {
// Serialize to JSON
MyClass obj = MyClass(42);
String json = jsonEncode(obj);
// Deserialize from JSON
MyClass obj2 = MyClass.fromJson(jsonDecode(json));
}