Cause `UnresolvedType` is not a subtype of type `T(Generic)` in type cast error

[UkiDelly]

I was trying to use generic to decode the json into a different model depending on the data I received from the network communication. The problem is when it try to decode from json (either string and map), it cause an error of

UnresolvedType is not a subtype of T(Generic type) in type cast

How could I solve this problem?

This is the BaseResponse model that I use to convert the response from the network.

@MappableClass()
final class BaseResponse<T> with BaseResponseMappable {
  const BaseResponse({
    this.success,
    this.error,
  });

  final SuccessModel? success;
  final ErrorModel? error;

  factory BaseResponse.fromJson(Map<String, dynamic> map) => BaseResponseMapper.fromMap(map);

  factory BaseResponse.fromJsonString(String json) => BaseResponseMapper.fromJson(json);
}

And also SuccessModel is using generic too

@MappableClass()
final class SuccessModel<T> with SuccessModelMappable {
  const SuccessModel({
    required this.data,
    required this.resultCode,
    required this.resultMessage,
  });

  final T? data;
  final int resultCode;
  final String resultMessage;

  factory SuccessModel.fromJson(Map<String, dynamic> map) => SuccessModelMapper.fromMap(map);
  factory SuccessModel.fromJsonString(String json) => SuccessModelMapper.fromJson(json);
}

I am using this TermModel to test it

@MappableClass()
final class TermModel with TermModelMappable {
  const TermModel({
    required this.agid,
    this.deleted,
    this.lid,
    required this.name,
    this.cid,
    this.cidName,
    this.content,
    this.sortNo,
    this.required,
    this.requiredName,
    this.modate,
    this.regdate,
    this.isChecked = false,
  });
  final int agid;
  final int? deleted;
  final int? lid;
  final String name;
  final int? cid;
  final String? cidName;
  final String? content;
  final int? sortNo;
  final int? required;
  final String? requiredName;
  final String? modate;
  final String? regdate;
  final bool isChecked;

  factory TermModel.fromJson(Map<String, dynamic> map) => TermModelMapper.fromMap(map);
  factory TermModel.fromJsonString(String json) => TermModelMapper.fromJson(json);
}

This is the code I test

import 'dart:convert';
import 'package:http/http.dart' hide BaseResponse;

Future<void> main(List<String> arguments) async {
  final response = await get(Uri.parse("my server api"));

  // decode to Map
  final encodeBody = jsonDecode(response.body);

  print(encodeBody);
  final res = BaseResponse<List<TermModel>>.fromJson(encodeBody);
  print(res.success);
}

Then this is the output

[schultek]

Any class used through a generic type must be initialized beforehand.

Do TermModelMapper.ensureInitialized()

[UkiDelly]

In this situation, there is only one TermModelMapper, but if there are more models used as generics, will there be no choice but to hardcode .ensureInitialized() of all models?

[schultek]

Check out https://pub.dev/documentation/dart_mappable/latest/topics/Generics-topic.html#generated-initializer

Unfortunately this can't be done fully automatically since Dart does not have static initialization of classes.