为啥 Flutter 导入提供程序包不起作用？

Posted 2023-03-12

【中文标题】为啥 Flutter 导入提供程序包不起作用？

【英文标题】：Why is Flutter import provider package not working?为什么 Flutter 导入提供程序包不起作用？

【发布时间】：2020-02-24 20:14:16

【问题描述】：

所以按照这个教程在 Flutter 中做一个简单的登录 UI

https://medium.com/better-programming/simple-firebase-login-flow-in-flutter-6f44c2b5c58a

显然，flutter 中的这个包没有被正确导入。不工作的特定行是这 3 行代码

import 'package:provider/provider.dart';
ChangeNotifierProvider<AuthService>( //TODO: authservices and provider pages
future: Provider.of<AuthService>(context).getUser(),

我一直在搜索一堆并尝试阅读文档，但无法得到任何简单的答案，但无论如何感谢任何给我答案的人

import 'package:flutter/material.dart';
    import 'package:provider/provider.dart';
    import 'home_page.dart';
    import 'auth.dart';
    import 'login_page.dart';

void main() => runApp(
  ChangeNotifierProvider<AuthService>( //TODO: authservices and provider pages
    child: MyApp(),
    builder: (BuildContext context) 
      return AuthService();
    ,
  ),
);

class MyApp extends StatelessWidget 
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) 
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primarySwatch: Colors.blue),
      home: FutureBuilder(
        future: Provider.of<AuthService>(context).getUser(),
        builder: (context, AsyncSnapshot snapshot) 
          if (snapshot.connectionState == ConnectionState.done) 
            return snapshot.hasData ? HomePage() : LoginPage();
           else 
            return Container(color: Colors.white);
          
        ,
      ),
    );
  

供任何人查看的 pubspec.yaml 文件

name: login_flutter_app
description: A new Flutter application.

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In ios, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2

dev_dependencies:
  flutter_test:
    sdk: flutter


# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

【问题讨论】：

你的pubspec.yaml是什么样的？

name: login_flutter_app description: A new Flutter application. version: 1.0.0+1 environment: sdk: ">=2.1.0 <3.0.0" dependencies: flutter: sdk: flutter cupertino_icons: ^0.1.2 dev_dependencies: flutter_test: sdk: flutter flutter: # The following line ensures that the Material Icons font is # included with your application, so that you can use the icons in # the material Icons class. uses-material-design: true

大部分cmets我都拿出来了，不过就是这个样子

您需要在 pubspec.yaml 依赖项中包含提供程序

【参考方案1】：

必须将这些放入项目中

cupertino_icons: ^0.1.2 颤振蓝：^0.6.3+1 提供者：^4.0.4

【参考方案2】：

只需在 pubspec.yaml 文件中添加依赖 provider: ^4.1.1 即可。它看起来像波纹管

dependencies:
  flutter:
   sdk: flutter
  provider: ^4.1.1