在“MultiBlocProvider”中使用“BlocBuilder”时出现错误

Question

我是 Flutter 的新手。我尝试使用谷歌搜索，但无法解决我的问题。我使用“MultiBlocProvider”来管理统计信息。我想像下面这样改变暗模式状态。

ThemeCubit.dart

part 'theme_state.dart';

class ThemeCubit extends HydratedCubit<ThemeState> {
   ThemeCubit() : super(ThemeState(AppThemes.lightTheme));

   void getTheme(ThemeState state) {
       emit(state);
   }

  @override
  ThemeState? fromJson(Map<String, dynamic> json) {
    return json['isDark'] as bool
        ? ThemeState(AppThemes.darkTheme)
        : ThemeState(AppThemes.lightTheme);
  }

 @override
 Map<String, bool>? toJson(ThemeState state) {
    return {'isDark': state.themeData.brightness == Brightness.dark};
 }
}

ThemeState.dart

part of 'theme_cubit.dart';

@immutable
class ThemeState extends Equatable {
  final ThemeData themeData;

  const ThemeState(this.themeData);

  @override
  List<Object?> get props => [themeData];
}

ma​​in.dart

class MyApp extends StatelessWidget {
     const MyApp({Key? key}) : super(key: key);

    // This widget is the root of your application.
    @override
    Widget build(BuildContext context) {
        return  MultiBlocProvider(
           providers: [
              BlocProvider(
                  lazy: true,
                 create: (context) => ThemeCubit(),
              ),
           ],
          child:BlocBuilder<ThemeCubit, ThemeState>(
             builder: (context,state) {
                 return MaterialApp(           
                     debugShowCheckedModeBanner: false,            
                     title: 'Flutter Production Boilerplate',
                     theme: state.themeData, //ThemeMode.dark,
                     home: const MyHomePage(title: 'Flutter Demo Home Page'),
                 );
                },
               ),
              );
            }
         }

settingScreen.dart

Positioned(
                  top: 60 - widget.offset / 2,
                  left: 20,
                  child: Builder(builder: (context) {

                    return Switch(
                        value:newValue ,
                        onChanged: (value) {
                          BlocProvider.of<ThemeCubit>(context).getTheme(ThemeState(
                              newValue ? AppThemes.darkTheme : AppThemes.lightTheme));
                        });
                  })
            ),

此代码在使用 "BlocProvider" 时可以正常工作。但是当我使用“MultiBlocProvider”时，出现以下错误。

以下断言被抛出附加到渲染树： 'package:flutter/src/widgets/framework.dart'：断言失败：行 4357 pos 14：'owner!._debugCurrentBuildTarget == this'：不正确。

要么断言表明框架本身存在错误，要么我们 应在此错误消息中提供更多信息 帮助您确定并解决根本原因。在任一情况下， 请在 GitHub 上提交错误报告此断言：
https://github.com/flutter/flutter/issues/new?template=2_bug.md

当异常被抛出时，这是堆栈： #2 元素重建。 （包：flutter/src/widgets/framework.dart:4357:14） #3 Element.rebuild (package:flutter/src/widgets/framework.dart:4360:6) #4 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4643:5) #5 ComponentElement.mount (package:flutter/src/widgets/framework.dart:4638:5) #6 Element.inflateWidget (package:flutter/src/widgets/framework.dart:3673:14) #7 Element.updateChild (package:flutter/src/widgets/framework.dart:3425:18) #8 RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1198:16) #9 RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:1167:5) #10 RenderObjectToWidgetAdapter.attachToRenderTree。 （包：flutter/src/widgets/binding.dart:1112:18） #11 BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2573:19) #12 RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:1111:13) #13 WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:944:7) #14 WidgetsBinding.scheduleAttachRootWidget。 (package:flutter/src/widgets/binding.dart:924:7) (省略13帧 来自 _AssertionError 类、_RawReceivePortImpl 类、_Timer 类、 dart:async 和 dart:async-patch)

我该如何解决？

Answer 1

我在 ThemeCubit.dart 中添加了以下代码：

 bool isDarkMode = false;
 ThemeMode currentTheme(){
 isDarkMode?_setTheme(ThemeMode.dark) : _setTheme(ThemeMode.light);

      return isDarkMode?ThemeMode.dark : ThemeMode.light;
 }

 void updateTheme(bool isDarkMode) {
 this.isDarkMode = isDarkMode;

}

并更改 ma​​in.dart ：

  Widget build(BuildContext context) {
     return  MultiBlocProvider(
        providers: [
           BlocProvider(
             create: (context) => ThemeCubit(),
          ),
       ],
       child:ElderlyApp(),     
    );
  }
  class ElderlyApp extends StatefulWidget {
     const ElderlyApp({Key? key,}) : super(key: key);
     @override
     _ElderlyAppState createState() => _ElderlyAppState();
  }

  class _ElderlyAppState extends State<ElderlyApp> with WidgetsBindingObserver {

     @override
       void initState() {
           WidgetsBinding.instance!.addObserver(this);
           super.initState();
       }

      @override
     void didChangePlatformBrightness() {
        context.read<ThemeCubit>().currentTheme();
       super.didChangePlatformBrightness();
     }

     @override
     void dispose() {
        WidgetsBinding.instance!.removeObserver(this);
        super.dispose();
    }
    @override
    Widget build(BuildContext context) {
        return MaterialApp(
        title: 'Flutter Production Boilerplate',
        theme: AppThemes.lightTheme,
        darkTheme: AppThemes.darkTheme,
        themeMode: context.select(
          (ThemeCubit cubit) => cubit.currentTheme()), //ThemeMode.dark,
        debugShowCheckedModeBanner: false,
        home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
   }
  }

并更改 seetingScreen.dart

中的代码

Positioned(
   top: 60 - widget.offset / 2,
   left: 20,
   child: Builder(builder: (context) {
   bool isDark = context.select((ThemeCubit themeCubit) =>
               themeCubit.state.themeMode) ==ThemeMode.dark ? true: false;
   return Switch(
                value: context.read<ThemeCubit>().isDarkMode,
                onChanged: (value) {
                context.read<ThemeCubit>().updateTheme(value);
              });
    })),