Motivation

The toString() method is useful for a logging but its default implementation doesn't generate a readable string. But overriding every single class's toString() method is a tedious task and doesn't scale well. PrettyJsonMixin overrides the toString() method and return a pretty json formatted string.

Getting started

Implement the toJson() method, then the toString() will automatically produce a pretty json string.

class User with PrettyJsonMixin {
  User({
    required this.id,
    required this.name,
  });

  final String id;
  final String name;

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

void main() {
  final user = User(
    id: '1',
    name: 'Hello World!',
  );
  print(user.toString());
  // Prints
  // {
  // "id": "1",
  // "name": "Hello World!"
  // }
}

You wouldn't want to implement the toJson() method by yourself. Use the json_serializable package and auto-generate the toJson() method.

@JsonSerializable()
class User with PrettyJsonMixin {
  User({
    required this.id,
    required this.name,
  });

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

  @override
  Map<String, dynamic> toJson() => _$UserToJson(this);

  final String id;
  final String name;
}

void main() {
  final user = User(
    id: '1',
    name: 'Hello World!',
  );
  print(user.toString());
  // Prints
  // {
  // "id": "1",
  // "name": "Hello World!"
  // }
}

Additional information

The implementation for the PrettyJsonMixin is nothing more than the below. If you don't want to add an extra external dependency, then just feel free to copy and paste the below code.

mixin PrettyJsonMixin {
  Map<String, dynamic> toJson();

  @override
  String toString() {
    final encoder = JsonEncoder.withIndent(' ' * 2);
    return encoder.convert(toJson());
  }
}