Flutter项目Firebase+GetStorage状态更新报错：_JsonDocumentReference异常

问题1：数据库更新成功，但抛出序列化异常 #

控制台报错：

E/flutter ( 2958): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: Converting object to an encodable object failed: Instance of '_JsonDocumentReference'
E/flutter ( 2958): #0      _JsonStringifier.writeObject (dart:convert/json.dart:794:7)
E/flutter ( 2958): #1      _JsonStringifier.writeMap (dart:json.dart:875:7)
E/flutter ( 2958): #2      _JsonStringifier.writeJsonValue (dart:json.dart:830:21)
E/flutter ( 2958): #3      _JsonStringifier.writeObject (dart:json.dart:785:9)
E/flutter ( 2958): #4      _JsonStringStringifier.printOn (dart:json.dart:983:17)
E/flutter ( 2958): #5      _JsonStringStringifier.stringify (dart:json.dart:968:5)
E/flutter ( 2958): #6      JsonEncoder.convert (dart:json.dart:345:30)
E/flutter ( 2958): #7      JsonCodec.encode (dart:json.dart:231:45)
E/flutter ( 2958): #8      StorageImpl.flush (package:get_storage/src/storage/io.dart:34:37)
E/flutter ( 2958): #9      GetStorage._flush (package:get_storage/src/storage_impl.dart:144:23)
E/flutter ( 2958): #10     GetQueue._check (package:get/get_utils/src/queue/get_queue.dart:42:47)
E/flutter ( 2958): #11     GetQueue.add (package:get/get_utils/src/queue/get_queue.dart:29:5)
E/flutter ( 2958): #12     GetStorage._addToQueue (package:get_storage/src/storage_impl.dart:139:18)
E/flutter ( 2958): #13     Microtask.exec.<anonymous closure> (package:get_storage/src/storage_impl.dart:174:17)
E/flutter ( 2958): #14     _microtaskLoop (dart:async/schedule_microtask.dart:40:21)
E/flutter ( 2958): #15     _startMicrotaskLoop (dart:async/schedule_microtask.dart:49:5)

原因 #

你在addStatus方法中把Firestore的DocumentReference对象（userstatus变量）直接写入了GetStorage，而GetStorage只支持存储可JSON序列化的数据类型（如Map、String、int等），DocumentReference是不可序列化的对象，因此触发序列化失败。

问题2：进入Profile页面触发NoSuchMethodError，热重载后消失 #

控制台报错：

======== Exception caught by widgets library =======================================================
The following NoSuchMethodError was thrown building Profile(dirty):
Class '_JsonDocumentReference' has no instance method '[]'.
Receiver: Instance of '_JsonDocumentReference'
Tried calling: []("status")

The relevant error-causing widget was: 
  Profile Profile:file:///D:/FIVERR%20PROJECTS%20FLUTTER/helping_hand/helping_hand/lib/drawers/Slidedrawer.dart:22:20
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:38:5)
#1      Profile.build (package:helping_hand/UI/Other/Profile.dart:65:120)
#2      StatelessElement.build (package:flutter/src/widgets/framework.dart:4949:49)
#3      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4878:15)
#4      Element.rebuild (package:flutter/src/widgets/framework.dart:4604:5)
#5      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4859:5)
#6      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4853:5)
...     Normal element mounting (275 frames)

原因 #

因为GetStorage中存储的是DocumentReference对象，你在Profile页面尝试用['status']这个Map的操作符去访问它的属性，而DocumentReference根本没有这个方法，所以报错。热重载后暂时消失是因为缓存被重置，但问题根源未解决。

修复方案 #

核心修改：不要存储Firestore的引用对象，直接存储需要的状态数据

修改BarController.dart中的addStatus方法 #

把写入GetStorage的对象从DocumentReference改成传入的userStatus Map：

// status
Future<void> addStatus(Map<String,String> userStatus) async {
  loadingbar();
  try{
    final DocumentReference userstatus= FirebaseFirestore.instance
        .collection('users')
        .doc(Auth().currentuser?.email);
    await userstatus.update({
      "status":userStatus['status'],"description":userStatus['description'],
    });
    // 原代码：Userbox.write('userStatus', userstatus);
    // 修改为：直接存储userStatus这个可序列化的Map
    Userbox.write('userStatus', userStatus);
  }catch(e){
    if (kDebugMode) {
      print('add status error ::: $e');
    }
      Get.snackbar('error','we have encountered an error');
  }

  loadingbaroff();
}

bool isloading = false;

void loadingbar() {
  isloading = true;
  update();
}
void loadingbaroff() {
  isloading = false;
  update();
}

验证Profile页面 #

修改后，Profile页面的代码不需要改动，因为现在GetStorage中存储的是Map<String,String>类型的数据，可以正常用['status']和['description']访问属性：

Container(
  alignment: Alignment.centerLeft,
  padding: const EdgeInsets.only(top: 24,bottom: 12,left: 24,right: 12),
  child: Text('User status : ${Userbox.read('userStatus') == null? 'not fetched':Userbox.read('userStatus')['status']}',
    style: const TextStyle(color: Colors.redAccent,fontWeight: FontWeight.normal,fontSize: 16),),),
Container(
  alignment: Alignment.centerLeft,
  padding: const EdgeInsets.only(top: 24,bottom: 12,left: 24,right: 12),
  child: Text('status description : ${Userbox.read('userStatus')== null?'not fetched':Userbox.read('userStatus')['description']}',
    style: const TextStyle(color: Colors.redAccent,fontWeight: FontWeight.normal,fontSize: 16),),),

内容的提问来源于stack exchange，提问作者Abhiram