Flutter使用json_serializable传参时类型转换异常问题求助

问题背景 #

• 基于json_serializable: ^6.3.1自动生成toJson()和fromJson()方法，定义了继承自DetailedRequest的MaintenanceSuperRequest类，其中包含List<MaintenanceRequest>类型的maintenanceRequestsList字段；MaintenanceRequest类也已生成对应序列化方法。
• 使用get: ^4.6.3做状态管理，通过Get.toNamed('rootName', arguments: object.toJson())传递对象数据，但调用maintenanceSuperRequest = MaintenanceSuperRequest.fromJson(Get.arguments)时抛出异常：

  Exception type 'MaintenanceRequest' is not a subtype of type 'Map<String, dynamic>' in type cast
  

错误栈信息 #

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)

补充细节 #

• 从API获取数据时，使用(json.decode(response.body) as List).map((data) => MaintenanceSuperRequest.fromJson(data)).toList()可正常解析。
• 查看MaintenanceSuperRequest.toJson()生成的数据发现，maintenanceRequestsList中的元素并非Map格式，而是MaintenanceRequest对象的字符串形式：

args {
//...... 其他数据    
services: [Safety, Plumbing, Elevator, Landline_Satellite],

maintenanceRequestsList: [SP Key 121212121266xy@s.com
Cost 50.0
Service Safety
Is Completed false, SP Key 121212121266xy@s.com
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]}

解决方案 #

问题根源 #

MaintenanceSuperRequest类中maintenanceRequestsList字段的序列化配置存在问题，导致toJson()没有将列表内的MaintenanceRequest对象转换为Map，而是直接调用了对象的toString()方法生成字符串元素，反序列化时无法将字符串转为Map，因此抛出类型转换异常。

修复步骤 #

1. 检查并修正序列化注解
   确保MaintenanceSuperRequest类的注解配置正确，让json_serializable能够正确处理列表中的MaintenanceRequest对象：

   import 'package:json_annotation/json_annotation.dart';
   import 'maintenance_request.dart';
   
   part 'maintenance_super_request.g.dart';
   
   @JsonSerializable()
   class MaintenanceSuperRequest extends DetailedRequest {
     final List<MaintenanceRequest> maintenanceRequestsList;
   
     MaintenanceSuperRequest({required this.maintenanceRequestsList});
   
     factory MaintenanceSuperRequest.fromJson(Map<String, dynamic> json) =>
         _$MaintenanceSuperRequestFromJson(json);
   
     @override
     Map<String, dynamic> toJson() => _$MaintenanceSuperRequestToJson(this);
   }
   

   注意：若MaintenanceRequest类不在同一文件，需确保正确导入，且该类的toJson()方法能正常生成Map格式数据。

2. 重新生成序列化代码
   执行以下命令重新生成.g.dart文件，确保注解生效：

   flutter pub run build_runner build --delete-conflicting-outputs
   

3. 验证序列化结果
   再次调用object.toJson()，检查maintenanceRequestsList的元素是否为Map格式，而非字符串。

4. 可选优化：直接传递对象
   GetX支持直接传递对象，无需手动序列化/反序列化，可简化流程：

   • 传递时：Get.toNamed('rootName', arguments: object)
   • 接收时：maintenanceSuperRequest = Get.arguments as MaintenanceSuperRequest
     这种方式避免了序列化过程中可能出现的问题，更简洁高效。

内容的提问来源于stack exchange，提问作者Abanoub Refaat