Flutter框架实现登录注册功能，不连接数据库

要在Flutter框架中实现登录和注册功能，而不连接数据库，可以使用本地存储来存储用户信息。以下是一个简单的示例，演示如何使用本地存储来实现登录和注册功能。

首先，我们需要添加 shared_preferences 插件到 pubspec.yaml 文件中：

dependencies:flutter:sdk: fluttershared_preferences: ^0.5.13+4

然后，在 lib 文件夹中创建一个新的文件夹 models，并在其中创建一个名为 user.dart 的文件。在 user.dart 文件中，定义一个简单的 User 类，用于表示用户信息：

class User {final String username;final String password;User({required this.username, required this.password});
}

接下来，我们将在 lib 文件夹中创建一个名为 utils.dart 的文件，在其中定义一些工具函数。首先，我们将创建一个函数来保存用户信息到本地存储：

import 'package:shared_preferences/shared_preferences.dart';
import 'package:your_app_name/models/user.dart';class Utils {static Future<void> saveUser(User user) async {final prefs = await SharedPreferences.getInstance();await prefs.setString('username', user.username);await prefs.setString('password', user.password);}
}

然后，我们将创建一个函数来从本地存储中获取保存的用户信息：

class Utils {// ...static Future<User?> getUser() async {final prefs = await SharedPreferences.getInstance();final username = prefs.getString('username');final password = prefs.getString('password');if (username != null && password != null) {return User(username: username, password: password);}return null;}
}

现在，我们将在 lib 文件夹中创建一个名为 login.dart 的文件，在其中实现登录功能。首先，我们将创建一个简单的登录表单：

import 'package:flutter/material.dart';
import 'package:your_app_name/models/user.dart';
import 'package:your_app_name/utils.dart';class LoginScreen extends StatefulWidget {@override_LoginScreenState createState() => _LoginScreenState();
}class _LoginScreenState extends State<LoginScreen> {final _formKey = GlobalKey<FormState>();String _username = '';String _password = '';@overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text('Login'),),body: Padding(padding: EdgeInsets.all(16.0),child: Form(key: _formKey,child: Column(children: [TextFormField(decoration: InputDecoration(labelText: 'Username'),validator: (value) {if (value == null || value.isEmpty) {return 'Please enter your username';}return null;},onSaved: (value) => _username = value!,),TextFormField(decoration: InputDecoration(labelText: 'Password'),obscureText: true,validator: (value) {if (value == null || value.isEmpty) {return 'Please enter your password';}return null;},onSaved: (value) => _password = value!,),SizedBox(height: 16.0),ElevatedButton(onPressed: () {if (_formKey.currentState!.validate()) {_formKey.currentState!.save();_login();}},child: Text('Login'),),],),),),);}void _login() async {final user = await Utils.getUser();if (user != null && user.username == _username && user.password == _password) {// 登录成功showDialog(context: context,builder: (BuildContext context) {return AlertDialog(title: Text('Success'),content: Text('Logged in successfully'),actions: [TextButton(child: Text('OK'),onPressed: () {Navigator.of(context).pop();},),],);},);} else {// 登录失败showDialog(context: context,builder: (BuildContext context) {return AlertDialog(title: Text('Error'),content: Text('Invalid credentials'),actions: [TextButton(child: Text('OK'),onPressed: () {Navigator.of(context).pop();},),],);},);}}
}

然后，我们将在 lib 文件夹中创建一个名为 register.dart 的文件，在其中实现注册功能。类似地，我们将创建一个简单的注册表单：

import 'package:flutter/material.dart';
import 'package:your_app_name/models/user.dart';
import 'package:your_app_name/utils.dart';class RegisterScreen extends StatefulWidget {@override_RegisterScreenState createState() => _RegisterScreenState();
}class _RegisterScreenState extends State<RegisterScreen> {final _formKey = GlobalKey<FormState>();String _username = '';String _password = '';@overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text('Register'),),body: Padding(padding: EdgeInsets.all(16.0),child: Form(key: _formKey,child: Column(children: [TextFormField(decoration: InputDecoration(labelText: 'Username'),validator: (value) {if (value == null || value.isEmpty) {return 'Please enter your username';}return null;},onSaved: (value) => _username = value!,),TextFormField(decoration: InputDecoration(labelText: 'Password'),obscureText: true,validator: (value) {if (value == null || value.isEmpty) {return 'Please enter your password';}return null;},onSaved: (value) => _password = value!,),SizedBox(height: 16.0),ElevatedButton(onPressed: () {if (_formKey.currentState!.validate()) {_formKey.currentState!.save();_register();}},child: Text('Register'),),],),),),);}void _register() async {final newUser = User(username: _username, password: _password);await Utils.saveUser(newUser);showDialog(context: context,builder: (BuildContext context) {return AlertDialog(title: Text('Success'),content: Text('Registered successfully'),actions: [TextButton(child: Text('OK'),onPressed: () {Navigator.of(context).pop();Navigator.of(context).pop(); // 返回登录页面},),],);},);}
}

最后，在 lib 文件夹中的 main.dart 文件中，我们将创建一个简单的登陆注册示例应用，包含一个首页和两个路由：/login 和 /register。用户可以从首页导航到登录和注册页面：

import 'package:flutter/material.dart';
import 'package:your_app_name/login.dart';
import 'package:your_app_name/register.dart';void main() {runApp(MyApp());
}class MyApp extends StatelessWidget {@overrideWidget build(BuildContext context) {return MaterialApp(title: 'Login & Register Demo',theme: ThemeData(primarySwatch: Colors.blue,),initialRoute: '/',routes: {'/': (context) => HomeScreen(),'/login': (context) => LoginScreen(),'/register': (context) => RegisterScreen(),},);}
}class HomeScreen extends StatelessWidget {@overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text('Home'),),body: Center(child: Column(mainAxisAlignment: MainAxisAlignment.center,children: [ElevatedButton(onPressed: () {Navigator.pushNamed(context, '/login');},child: Text('Login'),),ElevatedButton(onPressed: () {Navigator.pushNamed(context, '/register');},child: Text('Register'),),],),),);}
}