带有抽象类的Dart JsonSerializable

Question

我正在尝试为一个对象生成我的json助手函数，该对象包含一个具有抽象类类型的列表，如下所示：

import 'package:json_annotation/json_annotation.dart';

import 'exercise-variations.a.dart';

part 'routine.model.g.dart';

@JsonSerializable()
class Routine {

  List<ExerciseRoutine> exercises;

  Routine();

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

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

    import 'package:json_annotation/json_annotation.dart';
    import 'exercise-variations.a.dart';

    part 'base-exercise-routine.g.dart';

    @JsonSerializable()
    class BaseExerciseRoutine implements ExerciseRoutine {
      int sets;

      BaseExerciseRoutine();

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

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

abstract class ExerciseRoutine {}

这样我就会得到这个错误：

[INFO] Running build...
[SEVERE] json_serializable:json_serializable on lib/test/routine.model.dart:
Error running JsonSerializableGenerator
Could not generate `fromJson` code for `exercises` because of type `ExerciseRoutine`.
None of the provided `TypeHelper` instances support the defined type.
package:dojohub_app_flutter/test/routine.model.dart:11:25
   ╷
11 │   List<ExerciseRoutine> exercises;
   │                         ^^^^^^^^^
   ╵
[INFO] Running build completed, took 1.2s

[INFO] Caching finalized dependency graph...
[INFO] Caching finalized dependency graph completed, took 92ms

[SEVERE] Failed after 1.3s
pub finished with exit code 1

这是有道理的，因为ExerciseRoutine没有实现toJson函数和fromJson工厂。也许我可以向我的抽象类添加一个toJson函数，但是我如何修复缺少的fromJson工厂呢？

Answer 1

我通过为exercises字段编写一个自定义的fromJson和toJson函数解决了这个问题

part 'routine.model.g.dart';

@JsonSerializable()
class Routine extends WorkoutRoutine {

  @JsonKey(fromJson: exercisesFromJson, toJson: exercisesToJson)
  List<ExerciseRoutine> exercises;

  Routine();

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

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

List<ExerciseRoutine> exercisesFromJson(List<dynamic> json) {
  return json.map((e) {
    return BaseExerciseRoutine.fromJson(e);
  }).toList();
}

List<dynamic> exercisesToJson(List<ExerciseRoutine> exercises) {
  return exercises.map((e) {
    switch (exercises.runtimeType) {
      case BaseExerciseRoutine:
        return (e as BaseExerciseRoutine).toJson();
      default:
        return null;
        break;
    }
  }).toList();
}