Flutter deserialisation using generics error - flutter

Question

I am trying to deserialise and serialise a generic class in flutter using build_runner. The code I have written is as below:
import 'package:json_annotation/json_annotation.dart';
import 'api_response_message_model.dart';
part 'api_response_base_model.g.dart';
#JsonSerializable()
class ApiResponseBaseModel<T> {
#JsonKey(fromJson: _dataFromJson, toJson: _dataToJson)
T data;
ApiResponseMessageModel message;
ApiResponseBaseModel({this.data, this.message});
factory ApiResponseBaseModel.fromJson(Map<String, dynamic> json) =>
_$ApiResponseBaseModelFromJson(json);
T _dataFromJson<T>(Map<String, dynamic> input) =>
input['value'] as T;
Map<String, dynamic> _dataToJson<T>(T input) =>
{'value': input};
}
I am getting the error as below when running command flutter packages pub run build_runner build --delete-conflicting-outputs
Could not generate `fromJson` code for `data`.
None of the provided `TypeHelper` instances support the defined type.
package:premier_app/models/api_response_base_model.dart:10:5
╷
10│ T data;
│ ^^^^
╵
Please help me identify the problem and know the correct solution.
I also did tried the method mentioned here but no luck in removing the error - https://github.com/dart-lang/json_serializable/blob/7b40e9b04805bf921e4cebb87ec4ad7b8e1a2d29/json_serializable/test/generic_files/generic_class.dart#L20-L21

Answer 1

Please move the _dataFromJson & _dataToJson methods outside the scope of class ApiResponseBaseModel<T>.
Example:
import 'package:json_annotation/json_annotation.dart';
import 'api_response_message_model.dart';
part 'api_response_base_model.g.dart';
#JsonSerializable()
class ApiResponseBaseModel<T> {
#JsonKey(fromJson: _dataFromJson, toJson: _dataToJson)
T data;
ApiResponseMessageModel message;
ApiResponseBaseModel({this.data, this.message});
factory ApiResponseBaseModel.fromJson(Map<String, dynamic> json) =>
_$ApiResponseBaseModelFromJson(json);
}
T _dataFromJson<T>(Map<String, dynamic> input) =>
input['value'] as T;
Map<String, dynamic> _dataToJson<T>(T input) =>
{'value': input};
I did try out myself, works!
Generated methods look like:
// GENERATED CODE - DO NOT MODIFY BY HAND
part of 'api_response_base_model.dart';
// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************
ApiResponseBaseModel<T> _$ApiResponseBaseModelFromJson<T>(
Map<String, dynamic> json) {
return ApiResponseBaseModel<T>(
data: _dataFromJson(json['data'] as Map<String, dynamic>),
message: json['message'],
);
}
Map<String, dynamic> _$ApiResponseBaseModelToJson<T>(
ApiResponseBaseModel<T> instance) =>
<String, dynamic>{
'data': _dataToJson(instance.data),
'message': instance.message,
};