flutter dart JsonSerializable with inherited class

Question

I have the following two classes where one is extending from the other like this :

@JsonSerializable(nullable: true)
class Response {
  final String responseCode;
  final String responseMessage;
  final String errorLog;
  Response({this.errorLog, this.responseCode, this.responseMessage});
  factory Response.fromJson(Map<String, dynamic> json) =>
      _$ResponseFromJson(json);
}

.........................................................

 @JsonSerializable(nullable: false)
class Verify extends Response {
  Data data;
  Verify({
    this.data,
  });
  factory Verify.fromJson(Map<String, dynamic> json) => _$VerifyFromJson(json);
  Map<String, dynamic> toJson() => _$VerifyToJson(this);
}

and whenever I'm trying to read response class properties from Verify class, it's always null.

so please how to achieve this?

Boarish

datacontractjsonserializer is a .NET component that makes it possible to directly serialize .NET objects into JSON data. Since you are using flutter and dart and not c# or any other .Net language, I removed the tag. – Leftward

Answer 1

this one I have solved by passing the parameters to super in verify class constructor like this

@JsonSerializable()
class VerifyResponse extends Response {
  Data data;

  VerifyResponse({
    this.data,
    String responseCode,
    String responseMessage,
  }) : super(responseCode: responseCode, responseMessage: responseMessage);

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

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

and for the response class it remains the same

@JsonSerializable()
class Response {
  final String responseCode;
  final String responseMessage;

  Response({this.responseCode, this.responseMessage});

  factory Response.fromJson(Map<String, dynamic> json) =>
      _$ResponseFromJson(json);
}

it's a bit annoying but it's what it's.

Boarish

Answer 2

You should remove 'final' keyword from Response Class

@JsonSerializable(nullable: true)
    class Response {
      String responseCode;
      String responseMessage;
      String errorLog;
      Response({this.errorLog, this.responseCode, this.responseMessage});
      factory Response.fromJson(Map<String, dynamic> json) =>
           _$ResponseFromJson(json);
}

Grimaldi

Removing "final" keyword in base class members fixed it for me. Thanks! – Doone

why? what would be the point of removing final. it only means that this value will be taken from the contracture – Boarish

It does not make sense to remove final if the fields are intended to be immutable. – Pleistocene

Answer 3

It worked by adding super(); explicitly to the child class's constructor.

@JsonSerializable()
class VerifyResponse extends Response {
  Data data;

  VerifyResponse({
    this.data,
    String responseCode,
    String responseMessage,
    //No need to list all parent class properties
    }) : super();

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

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

Respecting

Answer 4

I would like to extend the answer as there are a couple more gotchas.

You can't use the super.responseCode syntax in the constructor:

Incorrect

  VerifyResponse({
    this.data,
    super.responseCode,
    super.responseMessage,
  })

Correct

  VerifyResponse({
    this.data,
    String responseCode,
    String responseMessage,
  }) : super(responseCode: responseCode, responseMessage: responseMessage);

You also have to define the type in the constructor, otherwise they get passed to the super constructor as dynamic:

Incorrect

  VerifyResponse({
    required this.data,
    required responseCode,
    required responseMessage,
  }) : super(responseCode: responseCode, responseMessage: responseMessage);

Correct

  VerifyResponse({
    required this.data,
    required String responseCode,
    required String responseMessage,
  }) : super(responseCode: responseCode, responseMessage: responseMessage);

Speciation