在此生成器小部件上方找不到正确的提供者<XYZ>

Question

我是 Flutter 和 Bloc 的新手。

我创建了一个虚拟预算应用程序，其中包含 2 个列表视图；收入和支出，其中将根据用户保存的内容填充相应的列表（例如，单击按钮将显示一个表单，用户可以在其中选择要输入的收入或支出以及保存后的金额，相关列表将被填充。）

我现在已经观看了有关如何在应用程序中创建“入职”旅程的视频教程。

我现在面临的问题是，当用户通过单击表单上的

save

 按钮来保存收入/费用时，我收到以下错误：

The following ProviderNotFoundException was thrown while handling a gesture:
Error: Could not find the correct Provider<FinanceBloc> above this Builder Widget

This happens because you used a `BuildContext` that does not include the provider
of your choice. There are a few common scenarios:

- You added a new provider in your `main.dart` and performed a hot-reload.
  To fix, perform a hot-restart.

- The provider you are trying to read is in a different route.

  Providers are "scoped". So if you insert of provider inside a route, then
  other routes will not be able to access that provider.

- You used a `BuildContext` that is an ancestor of the provider you are trying to read.

  Make sure that Builder is under your MultiProvider/Provider<FinanceBloc>.
  This usually happens when you are creating a provider and trying to read it immediately.

有几点需要注意：

- 要显示入门屏幕，我必须更改应用程序的运行方式，以前是：

    void main() {
        Bloc.observer = const GlobalApplicationObserver();
        runApp(MyApp());
    }

但现在是：

    void main() {
        Bloc.observer = const GlobalApplicationObserver();
        runApp(MaterialApp(home: OnboardingPageWidget()));
    }

MyApp()

本质上是一个目前有1个选项卡的

DefaultTabController

，选项卡显示的页面是有2个列表的屏幕。在此类的构建方法中返回 

BlocProvider

，在构建方法中是选项卡控制器页面/

这是我的入职课程：

import 'package:budgetapplication/main.dart';
import 'package:budgetapplication/repository/expenditure_repository.dart';
import 'package:flutter/material.dart';

//This is a private class
class _OnboardingPageState extends State<OnboardingPageWidget> {
  final PageController controller = PageController();
  bool isLastPage = false;

  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Container(
          padding: EdgeInsets.only(bottom: 80),
          child: PageView(
            controller: controller,
            onPageChanged: (index) {
              setState(() {
                isLastPage = index == 1;
              });
            },
            children: [
              Container(
                color: Colors.amber,
                child: Center(
                  child: Text('Page 1'),
                ),
              ),
              Container(
                color: Colors.red,
                child: Center(
                  child: Text('Page 2'),
                ),
              )
            ],
          ),
        ),
        bottomSheet: Container(
          padding: EdgeInsets.symmetric(horizontal: 10),
          child: Row(
            children: [
              isLastPage
                  ? TextButton(
                      child: Text('Finish!'),
                      onPressed: () async {
                        Navigator.of(context).pushReplacement(
                            MaterialPageRoute(builder: (context) => MyApp()));
                      },
                    )
                  : TextButton(
                      child: Text('Next'),
                      onPressed: () {
                        controller.nextPage(
                            duration: Duration(milliseconds: 500),
                            curve: Curves.bounceInOut);
                      },
                    )
            ],
          ),
        ));
  }
}

class OnboardingPageWidget extends StatefulWidget {
    @override
    State<OnboardingPageWidget> createState() => _OnboardingPageState();
}

我怀疑由于路由的原因，上下文正在丢失？不确定，但任何帮助将不胜感激！

Answer 1

我希望我正确理解这一点，我相信这可能对你有帮助。

在使用 BLoC 值之前，您需要像这样添加提供者：

 void main() {
 Bloc.observer = const GlobalApplicationObserver();

 runApp(
   BlocProvider(
   create: (context) => FinanceBloc(),  // Create your FinanceBloc
   child: MyApp(),  // Your main app widget
  ),
 );
}

通过像这样添加提供程序，您可以在整个小部件树中使用此 BLoC。您可以稍后根据您的要求对其进行自定义，以获得更好的性能。确保在添加新的块提供程序后热重载

但是简单来说，你必须先添加provider，然后才能使用它：

onPressed: () {
 final financeBloc = BlocProvider.of<FinanceBloc>(context);
 // Use your financeBloc here
 },

让我知道您仍然遇到此错误