微信公众号搜"智元新知"关注
微信扫一扫可直接关注哦！

Flutter：使用ProxyProvider传递数据时发生错误

分类：编程问答

如何解决Flutter：使用ProxyProvider传递数据时发生错误

我正在尝试构建一个类似于转换器网站的应用程序，在该网站中，您需要在文本字段中放置一个链接，但是除了转换它，您只能看到该信息。我使用ProxyProvider连接2个提供程序。我遵循了本教程（https://dev.to/paulhalliday/how-to-use-proxyprovider-with-flutter-3ifo）中有关如何使用ProxyProvider并出现错误的说明。 这是代码。 -main.dart 

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,theme: ThemeData(
        primarySwatch: Colors.blue,textTheme: ThemeData.light().textTheme.copyWith(
              headline1: TextStyle(
                fontSize: 16.0,fontWeight: FontWeight.bold,color: Colors.white,),headline2: TextStyle(
                fontSize: 16.0,bodyText1: TextStyle(fontSize: 18.0,fontWeight: FontWeight.w500),bodyText2: TextStyle(
                fontSize: 20.0,title: 'ID',home: MultiProvider(
        providers: [
          Provider(
            create: (context) => InputService(),ProxyProvider<InputService,Future<CoreData>>(
            update: (context,InputService inputService,Future<CoreData> questionsService) =>
                QuestionsService().fetchQuestion(inputService),],child: Userinput(),);
  }
}

-TextField代码

class UserInput extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    ScreenConfig().init(context);
    final TextEditingController _controller = TextEditingController();


    return Scaffold(
      body: Container(
        height: double.infinity,padding: EdgeInsets.symmetric(horizontal: 8.0),color: Colors.blueAccent,child: Column(
          mainAxisAlignment: MainAxisAlignment.center,children: [
            Text(
              'Enter ID here',style: Theme.of(context).textTheme.bodyText2,SizedBox(height: screenHeight(0.05),TextField(
              controller: _controller,decoration: Inputdecoration(
                hintText: 'ID',hintStyle: TextStyle(color: Colors.grey),fillColor: Colors.white,filled: true,border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(10.0),SizedBox(height: 10.0,RaisedButton(
              child: Text(
                'Enter',shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10.0),color: Colors.lightBlue,onpressed: () {
                GetInput(userInput: _controller.text);
                print(GetInput(userInput: _controller.text));
                Provider.of<InputService>(context,listen: false);
                Navigator.pushReplacement(context,MaterialPageRoute(builder: (context) => HomePage()));
              },);
  }
}

-显示JSON文件的地方

class HomePage extends StatelessWidget {
  Widget build(BuildContext context) {
    Future<CoreData> question = Provider.of<Future<CoreData>>(context);

    return FutureProvider(
          create: (BuildContext context) => question,child: Scaffold(
        backgroundColor: Colors.grey[100],body: question == null
            ? Center(child: CircularProgressIndicator())
            : CustomScrollView(
                slivers: [
                  CustomAppBar(),CustomList(),);
  }
}

-获取用户输入的提供者

class GetInput {

  String userInput;

  GetInput({@required this.userInput}); 
}

class InputService {
  GetInput getInput;
}

-序列化链接的JSON文件的提供程序

class QuestionsService {

  Future<CoreData> fetchQuestion(InputService inputService) async {
    final response = await http.get(inputService.getInput.userInput);
    var jsonResponse = convert.jsonDecode(response.body);
    CoreData parsedQuestions = CoreData.fromJson(jsonResponse);

    return parsedQuestions;
  }
}

-错误消息

I/Flutter (21927): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/Flutter (21927): The following ProviderNotFoundException was thrown building HomePage(dirty):
I/Flutter (21927): Error: Could not find the correct Provider<Future<CoreData>> above this HomePage Widget
I/Flutter (21927):
I/Flutter (21927): This likely happens because you used a `BuildContext` that does not include the provider
I/Flutter (21927): of your choice. There are a few common scenarios:
I/Flutter (21927):
I/Flutter (21927): - The provider you are trying to read is in a different route.
I/Flutter (21927):
I/Flutter (21927):   Providers are "scoped". So if you insert of provider inside a route,then
I/Flutter (21927):   other routes will not be able to access that provider.
I/Flutter (21927):
I/Flutter (21927): - You used a `BuildContext` that is an ancestor of the provider you are trying to read.
I/Flutter (21927):
I/Flutter (21927):   Make sure that HomePage is under your MultiProvider/Provider<Future<CoreData>>.
I/Flutter (21927):   This usually happen when you are creating a provider and trying to read it immediately.
I/Flutter (21927):
I/Flutter (21927):   For example,instead of:
I/Flutter (21927):
I/Flutter (21927):   ```
I/Flutter (21927):   Widget build(BuildContext context) {
I/Flutter (21927):     return Provider<Example>(
I/Flutter (21927):       create: (_) => Example(),I/Flutter (21927):       // Will throw a ProviderNotFoundError,because `context` is associated
I/Flutter (21927):       // to the widget that is the parent of `Provider<Example>`
I/Flutter (21927):       child: Text(context.watch<Example>()),I/Flutter (21927):     ),I/Flutter (21927):   }
I/Flutter (21927):   ```
I/Flutter (21927):
I/Flutter (21927):   consider using `builder` like so:
I/Flutter (21927):
I/Flutter (21927):   ```
I/Flutter (21927):   Widget build(BuildContext context) {
I/Flutter (21927):     return Provider<Example>(
I/Flutter (21927):       create: (_) => Example(),I/Flutter (21927):       // we use `builder` to obtain a new `BuildContext` that has access to the provider
I/Flutter (21927):       builder: (context) {
I/Flutter (21927):         // No longer throws
I/Flutter (21927):         return Text(context.watch<Example>()),I/Flutter (21927):       }
I/Flutter (21927):     ),I/Flutter (21927):   }
I/Flutter (21927):   ```
I/Flutter (21927):
I/Flutter (21927): If none of these solutions work,consider asking for help on StackOverflow:
I/Flutter (21927): https://stackoverflow.com/questions/tagged/Flutter
I/Flutter (21927):
I/Flutter (21927): The relevant error-causing widget was:
I/Flutter (21927):   HomePage
I/Flutter (21927):   file:///C:/Users/bryan/source/repos/Flutter%20Projects/testing/quizizz_cheat/lib/screens/user_input.dart:52:92
I/Flutter (21927):
I/Flutter (21927): When the exception was thrown,this was the stack:
I/Flutter (21927): #0      Provider._inheritedElementOf (package:provider/src/provider.dart:309:7)
I/Flutter (21927): #1      Provider.of (package:provider/src/provider.dart:261:30)
I/Flutter (21927): #2      HomePage.build (package:quiz/screens/home.dart:9:42)
I/Flutter (21927): #3      StatelessElement.build (package:Flutter/src/widgets/framework.dart:4644:28)
I/Flutter (21927): #4      ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4570:15)
I/Flutter (21927): #5      Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #6      ComponentElement._firstBuild (package:Flutter/src/widgets/framework.dart:4549:5)
I/Flutter (21927): #7      ComponentElement.mount (package:Flutter/src/widgets/framework.dart:4544:5)
I/Flutter (21927): ...     normal element mounting (132 frames)
I/Flutter (21927): #139    Element.inflateWidget (package:Flutter/src/widgets/framework.dart:3512:14)
I/Flutter (21927): #140    Element.updateChild (package:Flutter/src/widgets/framework.dart:3270:18)
I/Flutter (21927): #141    RenderObjectElement.updateChildren (package:Flutter/src/widgets/framework.dart:5648:32)
I/Flutter (21927): #142    MultiChildRenderObjectElement.update (package:Flutter/src/widgets/framework.dart:6189:17)
I/Flutter (21927): #143    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #144    ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4595:16)
I/Flutter (21927): #145    StatefulElement.performRebuild (package:Flutter/src/widgets/framework.dart:4743:11)
I/Flutter (21927): #146    Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #147    StatefulElement.update (package:Flutter/src/widgets/framework.dart:4775:5)
I/Flutter (21927): #148    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #149    ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4595:16)
I/Flutter (21927): #150    Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #151    ProxyElement.update (package:Flutter/src/widgets/framework.dart:4930:5)
I/Flutter (21927): #152    _InheritednotifierElement.update (package:Flutter/src/widgets/inherited_notifier.dart:183:11)
I/Flutter (21927): #153    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #154    SingleChildRenderObjectElement.update (package:Flutter/src/widgets/framework.dart:6068:14)
I/Flutter (21927): #155    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #156    ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4595:16)
I/Flutter (21927): #157    StatefulElement.performRebuild (package:Flutter/src/widgets/framework.dart:4743:11)
I/Flutter (21927): #158    Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #159    StatefulElement.update (package:Flutter/src/widgets/framework.dart:4775:5)
I/Flutter (21927): #160    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #161    SingleChildRenderObjectElement.update (package:Flutter/src/widgets/framework.dart:6068:14)
I/Flutter (21927): #162    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #163    SingleChildRenderObjectElement.update (package:Flutter/src/widgets/framework.dart:6068:14)
I/Flutter (21927): #164    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #165    ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4595:16)
I/Flutter (21927): #166    Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #167    StatelessElement.update (package:Flutter/src/widgets/framework.dart:4651:5)
I/Flutter (21927): #168    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #169    ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4595:16)
I/Flutter (21927): #170    Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #171    ProxyElement.update (package:Flutter/src/widgets/framework.dart:4930:5)
I/Flutter (21927): #172    Element.updateChild (package:Flutter/src/widgets/framework.dart:3257:15)
I/Flutter (21927): #173    ComponentElement.performRebuild (package:Flutter/src/widgets/framework.dart:4595:16)
I/Flutter (21927): #174    StatefulElement.performRebuild (package:Flutter/src/widgets/framework.dart:4743:11)
I/Flutter (21927): #175    Element.rebuild (package:Flutter/src/widgets/framework.dart:4286:5)
I/Flutter (21927): #176    BuildOwner.buildScope (package:Flutter/src/widgets/framework.dart:2673:33)
I/Flutter (21927): #177    WidgetsBinding.drawFrame (package:Flutter/src/widgets/binding.dart:913:20)
I/Flutter (21927): #178    RendererBinding._handlePersistentFrameCallback (package:Flutter/src/rendering/binding.dart:302:5)
I/Flutter (21927): #179    SchedulerBinding._invokeFrameCallback (package:Flutter/src/scheduler/binding.dart:1117:15)
I/Flutter (21927): #180    SchedulerBinding.handleDrawFrame (package:Flutter/src/scheduler/binding.dart:1055:9)
I/Flutter (21927): #181    SchedulerBinding._handleDrawFrame (package:Flutter/src/scheduler/binding.dart:971:5)
I/Flutter (21927): #185    _invoke (dart:ui/hooks.dart:251:10)
I/Flutter (21927): #186    _drawFrame (dart:ui/hooks.dart:209:3)
I/Flutter (21927): (elided 3 frames from dart:async)
I/Flutter (21927): 
I/Flutter (21927): ════════════════════════════════════════════════════════════════════════════════════════════════════

解决方法

错误告诉您Provider已“作用域”。因此，如果您在路由内插入提供商，则其他路由将无法访问该提供商。您需要使提供程序可以被使用它的所有小部件访问。与其将MultiProvider放在MaterialApp内，不如将其向上移动。 （将其放在MaterialApp上方）
尝试这样做：

MultiProvider(
        providers: [
          Provider(
            create: (context) => InputService(),),ProxyProvider<InputService,Future<CoreData>>(
            update: (context,InputService inputService,Future<CoreData> questionsService) =>
                QuestionsService().fetchQuestion(inputService),],child: MaterialApp(...
        ),

版权声明：本文内容由互联网用户自发贡献，该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务，不拥有所有权，不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容， 请发送邮件至 dio@foxmail.com 举报，一经查实，本站将立刻删除。

苹果市值2025年有望达4万亿美元
pythonJavaScriptjavaHTMLreactjsC#AndroidCSSNode.jssqlrpython-3.xMysqLjQueryc++pandasFlutterangularIOSdjangolinuxswifttypescript路由器JSON路由器设置无线路由器h3c华三华三路由器设置华三路由器电脑软件教程arraysdocker软件图文教程Cvue.jslaravelspring-bootreact-native