Flutter Serializing objects types problem

Question

I'm using the json_serializable: ^6.3.1 pub package to auto generate toJson() & FromJson()

and i'm having this class

import 'package:json_annotation/json_annotation.dart';

part 'maintenance_super_request.g.dart';

@JsonSerializable()
class MaintenanceSuperRequest extends DetailedRequest {
  // String? sp_key;
  final List<String> services;
  final Unit unit;
   double? totalCost;
//This List Of Another Custom Class
  List<MaintenanceRequest> maintenanceRequestsList;

   MaintenanceSuperRequest({
    required this.maintenanceRequestsList,
    required this.services,
    required this.unit,  
    this.totalCost,
  }) ;

And this it's auto generated code by the package

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'maintenance_super_request.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

MaintenanceSuperRequest _$MaintenanceSuperRequestFromJson(
        Map<String, dynamic> json) =>
    MaintenanceSuperRequest(
      maintenanceRequestsList: (json['maintenanceRequestsList']
              as List<dynamic>)
          .map((e) => MaintenanceRequest.fromJson(e as Map<String, dynamic>))
          .toList(),
      services:
          (json['services'] as List<dynamic>).map((e) => e as String).toList(),
      unit: Unit.fromJson(json['unit'] as Map<String, dynamic>),
      totalCost: (json['totalCost'] as num?)?.toDouble(),
    );

Map<String, dynamic> _$MaintenanceSuperRequestToJson(
        MaintenanceSuperRequest instance) =>
    <String, dynamic>{  
      'services': instance.services,
      'unit': instance.unit,
      'totalCost': instance.totalCost,
      'maintenanceRequestsList': instance.maintenanceRequestsList,
    };

    
      factory MaintenanceSuperRequest.fromJson(Map<String, dynamic> json) =>
          _$MaintenanceSuperRequestFromJson(json);
    
      @override
      Map<String, dynamic> toJson() => _$MaintenanceSuperRequestToJson(this);
    
    }

and this is the custom class used in a list in the above class

import 'package:json_annotation/json_annotation.dart';

part 'maintenance_request.g.dart';

@JsonSerializable()

class MaintenanceRequest {
  String? spKey;
  double? cost;
  String service;
  bool isCompleted;
  MaintenanceRequest({this.spKey,this.cost,this.service='',this.isCompleted=false});



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

  @override
  Map<String, dynamic> toJson() => _$MaintenanceRequestToJson(this);

}

and it's auto generated code

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'maintenance_request.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

MaintenanceRequest _$MaintenanceRequestFromJson(Map<String, dynamic> json) =>
    MaintenanceRequest(
      spKey: json['spKey'] as String?,
      cost: (json['cost'] as num?)?.toDouble(),
      service: json['service'] as String? ?? '',
      isCompleted: json['isCompleted'] as bool? ?? false,
    );

Map<String, dynamic> _$MaintenanceRequestToJson(MaintenanceRequest instance) =>
    <String, dynamic>{
      'spKey': instance.spKey,
      'cost': instance.cost,
      'service': instance.service,
      'isCompleted': instance.isCompleted,
    };

And I'm Using get: ^4.6.3 for state management, so in case i want to pass some data in navigation function i use this code

Get.toNamed('rootName',arguments:object.toJson());

but in case of those class when i try to retrieve the data from json using this line of code

maintenanceSuperRequest =MaintenanceSuperRequest.fromJson(Get.arguments);

it throws this error

Exception type 'MaintenanceRequest' is not a subtype of type 'Map<String, dynamic>' in type cast
Stack Trace 
#0      _$MaintenanceSuperRequestFromJson.<anonymous closure> (package:real_estate/models/requests/maintenance_req/maintenance_super_request.g.dart:14:53)
#1      MappedListIterable.elementAt (dart:_internal/iterable.dart:413:31)
#2      ListIterator.moveNext (dart:_internal/iterable.dart:342:26)
#3      new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:189:27)
#4      new _GrowableList.of (dart:core-patch/growable_array.dart:150:28)
#5      new List.of (dart:core-patch/array_patch.dart:51:28)
#6      ListIterable.toList (dart:_internal/iterable.dart:213:44)
#7      _$MaintenanceSuperRequestFromJson (package:real_estate/models/requests/maintenance_req/maintenance_super_request.g.dart:15:12)
#8      new MaintenanceSuperRequest.fromJson (package:real_estate/models/requests/maintenance_req/maintenance_super_request.dart:52:7)
#9      ConfirmMaintenanceCompletionController.onInit (package:real_estate/controllers/common/confirm_maintenance_completion_controller.dart:17:58)
#10     GetLifeCycleBase._onStart (package:get/get_instance/src/lifecycle.dart:66:5)
#11     InternalFinalCallback.call (package:get/get_instance/src/lifecycle.dart:12:26)
#12     GetInstance._startController (package:get/get_instance/src/get_instance.dart:253:16)
#13     GetInstance._initDependencies (package:get/get_instance/src/get_instance.dart:204:11)
#14     GetInstance.find (package:get/get_instance/src/get_instance.dart:301:17)
#15     GetInstance.put (package:get/get_instance/src/get_instance.dart:86:12)
#16     Inst.put (package:get/get_instance/src/extension_instance.dart:89:21)
#17     ConfirmMaintenanceCompletionPage.build (package:real_estate/views/common/confirm_maintenance_completion_page.dart:13:67)
#18     StatelessElement.build (package:flutter/src/widgets/framework.dart:4876:49)
#19     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4806:15)
#20     Element.rebuild (package:flutter/src/widgets/framework.dart:4529:5)
#21     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4787:5)
#22     ComponentElement.mount (package:flutter/src/widgets/framework.dart:4781:5)
#23     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3817:16)
#24     Element.updateChild (package:flutter/src/widgets/framework.dart:3551:18)
#25     SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:6215:14)
#26     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3817:16)
#27     Element.updateChild (package:flutter/src/widgets/framework.dart:3551:18)
#28     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4832:16)
#29     Element.rebuild (package:flutter/src/widgets/framework.dart:4529:5)
#30     ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4787:5)

it says here 'MaintenanceRequest' is not a subtype of type 'Map<String, dynamic>' in type cast but i have no idea how to fix this.

so can any one help me with that

NOTE it works fine when i retrieve data from api using this code

(json.decode(response.body) as List)
        .map((data) => MaintenanceSuperRequest.fromJson(data))
        .toList();

UPDATE

// Data From MaintenanceSuperRequest.toJson()

 args {
//...... Some other data    
services: [Safety, Plumbing, Elevator, Landline_Satellite],

maintenanceRequestsList: [SP Key [email protected]
Cost 50.0
Service Safety
Is Completed false, SP Key [email protected]
Cost 80.0
Service Plumbing
Is Completed false, SP Key 
Cost 0.0
Service Elevator
Is Completed false, SP Key 
Cost 0.0
Service Landline_Satellite
Is Completed false]}

it because your data is List not a Map. you already use it on your last code. with map() it means you are looping the list and convert json to object — pmatatias
– pmatatias, Commented Dec 7, 2022 at 15:46
@pmatatias i thought that this line is the problem too map((e) => MaintenanceRequest.fromJson(e as Map<String, dynamic>)) .toList(), but how can i fix it. — Abanoub Refaat
– Abanoub Refaat, Commented Dec 7, 2022 at 16:01
can you provide you example data ? i guse there a nested json there — pmatatias
– pmatatias, Commented Dec 7, 2022 at 16:10
@pmatatias yes there is a nested json from both MaintenanceSuperRequest.toJson() and its list List<MaintenanceRequest> which has the MaintenanceRequest.toJson() — Abanoub Refaat
– Abanoub Refaat, Commented Dec 8, 2022 at 13:42
@pmatatias please check the example data provided in the update — Abanoub Refaat
– Abanoub Refaat, Commented Dec 8, 2022 at 13:42

Abanoub Refaat · Accepted Answer · 2022-12-10 21:31:06Z

1

I Solved my problem it was an issue due to nested json and I found out a solution on another question here

in my case it was the super class which contains a list of another class (the nested json problem) has to declear on the top this line of code

@JsonSerializable(explicitToJson: true)

this the parameter explicitToJson set to true. based on the documentation here

If true, generated toJson methods will explicitly call toJson on nested objects.

answered Dec 10, 2022 at 21:31

Abanoub Refaat

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