Get null when using generic

[pcqpcq]

my json data:

{
    "resultCode": "0",
    "resultMessage": "success",
    "data": {
        "result": 5
    }
}

my base_response.dart and its part

import 'package:json_annotation/json_annotation.dart';

part 'base_response.g.dart';

@JsonSerializable()
class BaseResponse<T> extends Object with _$BaseResponseSerializerMixin {
  String resultCode;
  String resultMessage;
  @JsonKey(fromJson: _dataFromJson, toJson: _dataToJson)
  T data;

  BaseResponse(this.resultCode, this.resultMessage, this.data);

  factory BaseResponse.fromJson(Map<String, dynamic> json) => _$BaseResponseFromJson<T>(json);

}

T _dataFromJson<T>(Map<String, dynamic> input) => 
    input['value'] as T;

Map<String, dynamic> _dataToJson<T>(T input) =>
    {'value': input};

part of 'base_response.dart';

BaseResponse<T> _$BaseResponseFromJson<T>(Map<String, dynamic> json) {
  return new BaseResponse<T>(
      json['resultCode'] as String,
      json['resultMessage'] as String,
      json['data'] == null
          ? null
          : _dataFromJson(json['data'] as Map<String, dynamic>));
}

abstract class _$BaseResponseSerializerMixin<T> {
  String get resultCode;
  String get resultMessage;
  T get data;
  Map<String, dynamic> toJson() => <String, dynamic>{
        'resultCode': resultCode,
        'resultMessage': resultMessage,
        'data': data == null ? null : _dataToJson(data)
      };
}

my data class and its part

import 'package:json_annotation/json_annotation.dart';

part 'content.g.dart';

@JsonSerializable()
class Content extends Object with _$ContentSerializerMixin {
  int result;

  Content(this.result);

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

part of 'content.dart';

Content _$ContentFromJson(Map<String, dynamic> json) {
  return new Content(json['result'] as int);
}

abstract class _$ContentSerializerMixin {
  int get result;
  Map<String, dynamic> toJson() => <String, dynamic>{'result': result};
}

then, when I use it like this:

var out = new BaseResponse<Content>.fromJson(jsonDecode(json));

print(out.resultCode);  // <---- it's 0
print(out.resultMessage);  // <---- it's success
print(out.data);  // <---- it's null

why out.data is null? Am I missing something?

[pcqpcq]

or, what I need is a version of Flutter where build_runner is running w/ --preview-dart-2. according to #202 ?

if so, any workaround?

[kevmoo]

Insert a print in here to see what's happening...

factory BaseResponse.fromJson(Map<String, dynamic> json) {
print(json);
return  _$BaseResponseFromJson<T>(json);
}

[pcqpcq]

Thanks for reply. @kevmoo

and here is the output:

{resultCode: 0, resultMessage: success, data: {result: 5}}

[kevmoo]

Ah! You're grabbing value from the map – which is null. Not result.

[pcqpcq]

and, the input inside _dataFromJson is missing field 'value':

T _dataFromJson<T>(Map<String, dynamic> input) => 
    input['value'] as T;  // <-- there is no 'value' here

the input is:

Map (1 items)
  0:"result" -> 5
    key:"result"
    value:5

[kevmoo]

@pcqpcq – figure out what you're doing now?

[pcqpcq]

@kevmoo sorry, I don't get it 😂 what should I do now?

[kevmoo]

Either change your data to {"value": 5} or your code to

T _dataFromJson<T>(Map<String, dynamic> input) => 
    input['result'] as T;

[pcqpcq]

No, it's incorrect, input['result'] is 5, it's not T

[kevmoo]

Right. Uh. I'm saying your data and your code does not align. Your code expects a may with a value key, but you're giving it a map with a result key.

[pcqpcq]

ok, I see, thank you!

[blackraindrop]

@pcqpcq

T _dataFromJson<T>(Map<String, dynamic> input) => 
    input['value'] as T;

T _dataFromJson<T>(Map<String, dynamic> input) {
    if (T is Content) return new Content.fromJson(input);
    else if (T is ...) return ...
    else throw Exception("Unknow type");
}

[pcqpcq]

@jiangyu19871119 Thanks, but it's very ugly as it takes the problem to higher level code, like #116

T _dataFromJson<T>(Map<String, dynamic> input) {
    if (T is Content) return new Content.fromJson(input);  /// <-- this is what I don't want
    else if (T is ...) return ...
    else throw Exception("Unknow type");
}