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Flutter – Dart Freezed package: Missing toJson method in generated file causing InvalidType error

I followed the documentation’s step by step to add Freezed to a class:

import 'package:freezed_annotation/freezed_annotation.dart';

part 'autonomy_event.freezed.dart';
part 'autonomy_event.g.dart';

@freezed
class AutonomyEvent with _$AutonomyEvent {
  const factory AutonomyEvent({
    required int eventCode,
    required int timestamp,
  }) = _AutonomyEvent;

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

In Android Studio, I keep getting a InvalidType error at _$$AutonomyEventImplToJson in my generated freezed class autonomy_event.freezed.dart:

/// @nodoc
@JsonSerializable()
class _$AutonomyEventImpl implements _AutonomyEvent {

(...)

@override
  Map<String, dynamic> toJson() {
    return _$$AutonomyEventImplToJson(
      this,
    );
  }
}

The detailed error is:

The method ‘$$AutonomyEventImplToJson’ isn’t defined for the type
‘$AutonomyEventImpl’. Try correcting the name to the
name of an existing method, or defining a method named
‘_$$AutonomyEventImplToJson’.

I believe this error occurs due to autonomy_event.g.dart not generating the toJson method.

I tried adding @Freezed(toJson: true) instead of @freezed in my class file, however that didn’t help as well, as the toJson method still isn’t generated.

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    To fix your issue, you need to add @JsonSerializable(createToJson: true) to your factory method.

    When you do that, the ToJson method in your autonomy_event.g.dart will be generated, and the reference in autonomy_event.freezed.dart will be resolved.

    Complete class code:

    import 'package:freezed_annotation/freezed_annotation.dart';

part 'autonomy_event.freezed.dart';
part 'autonomy_event.g.dart';

@freezed
class AutonomyEvent with _$AutonomyEvent {
  @JsonSerializable(createToJson: true)
  const factory AutonomyEvent({
    required int eventCode,
    required int timestamp,
  }) = _AutonomyEvent;

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

  2. 0

    Alternative solution is make build.yaml in root level you can setting how to generate your model

    targets:
  $default:
    builders:
      freezed:freezed:
        generate_for:
          include:
            - lib/entity/** // Model folder path
      json_serializable:
        options:
          any_map: false
          checked: false
          constructor: ""
          create_factory: true
          create_to_json: true
          disallow_unrecognized_keys: false
          explicit_to_json: false
          field_rename: snake
          generic_argument_factories: false
          ignore_unannotated: false
          include_if_null: true

    don’t forget to add this in your dependencies

    dev_dependencies:
  json_serializable:

    Now when you run build runner it will generate every model by your setting without write @JsonSerializable(createToJson: true) to every model you have

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