错误：在此 Directioner 小部件上方找不到正确的 Provider<User>

Question

我在运行我的 Flutter 应用程序时遇到了这个错误，我不知道如何修复它。 我怀疑产生此错误的文件是“directioner.dart”，如果没有登录用户，它会显示登录屏幕或主页。 有什么线索吗？谢谢。

这是我的“directioner.dart”文件：

import 'package:empirica_qaqc/pages/home_page.dart';
import 'package:empirica_qaqc/pages/login_page.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

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

  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context);
    return user == null ? LoginPage() : HomePage();
  }
}

这是我的 main.dart 文件

import 'package:empirica_qaqc/pages/directioner.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        primaryColor: Color(0xff1e8735),
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: Directioner(),
    );
  }
}

我的“颤振医生 -v”输出：

[✓] Flutter (Channel stable, 1.22.1, on Mac OS X 10.15.6 19G2021, locale es-CL)
    • Flutter version 1.22.1 at /Users/ben/flutter
    • Framework revision f30b7f4db9 (13 days ago), 2020-10-08 10:06:30 -0700
    • Engine revision 75bef9f6c8
    • Dart version 2.10.1

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/ben/Library/Android/sdk
    • Platform android-30, build-tools 30.0.2
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 11.6)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 11.6, Build version 11E708
    • CocoaPods version 1.9.1

[✓] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 50.0.1
    • Dart plugin version 193.7547
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] VS Code (version 1.50.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.15.1

[✓] Connected device (1 available)
    • sdk gphone x86 arm (mobile) • emulator-5554 • android-x86 • Android 11 (API 30) (emulator)

• No issues found!

Answer 1

您好像忘记在小部件树中“提供”User 对象。

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter Demo',
      theme: ThemeData(
        primaryColor: Color(0xff1e8735),
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      // expose an object to be available down the widget tree
      home: Provider( 
        create: (_) => User(),
        child: Directioner(),
      ),
    );
  }
}

错误屏幕通常会给出解决此类问题的提示。