如何在flutter中使用SQFLite登录应用时检查用户凭据

dependencies:
  sqflite: ^2.0.0+3
  path: ^2.0.0

import 'dart:async';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';

class DatabaseHelper {
  static final DatabaseHelper _instance = DatabaseHelper.internal();
  factory DatabaseHelper() => _instance;

  static Database? _db;

  Future<Database?> get db async {
    if (_db != null) {
      return _db;
    }
    _db = await initDb();
    return _db;
  }

  DatabaseHelper.internal();

  Future<Database> initDb() async {
    String databasesPath = await getDatabasesPath();
    String path = join(databasesPath, 'my_app.db');

    // 打开数据库
    return await openDatabase(path, version: 1, onCreate: _onCreate);
  }

  void _onCreate(Database db, int version) async {
    // 创建表
    await db.execute('''
      CREATE TABLE users (
        id INTEGER PRIMARY KEY,
        username TEXT,
        password TEXT
      )
    ''');

    // 插入示例用户
    await db.rawInsert('''
      INSERT INTO users (id, username, password)
      VALUES (1, 'admin', 'password')
    ''');
  }

  Future<bool> checkCredentials(String username, String password) async {
    Database? dbClient = await db;
    var result = await dbClient!.query(
      'users',
      where: 'username = ? AND password = ?',
      whereArgs: [username, password],
    );
    return result.isNotEmpty;
  }
}

import 'package:flutter/material.dart';
import 'package:your_app/database_helper.dart';

class LoginPage extends StatelessWidget {
  final TextEditingController _usernameController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();

  void _login(BuildContext context) async {
    String username = _usernameController.text;
    String password = _passwordController.text;

    bool isValid = await DatabaseHelper().checkCredentials(username, password);

    if (isValid) {
      // 登录成功，导航到下一个页面
      Navigator.pushNamed(context, '/home');
    } else {
      // 显示错误消息
      showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: Text('登录失败'),
            content: Text('无效的用户名或密码'),
            actions: <Widget>[
              TextButton(
                child: Text('关闭'),
                onPressed: () {
                  Navigator.of(context).pop();
                },
              ),
            ],
          );
        },
      );
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('登录'),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: Column(
          children: <Widget>[
            TextField(
              controller: _usernameController,
              decoration: InputDecoration(
                labelText: '用户名',
              ),
            ),
            TextField(
              controller: _passwordController,
              decoration: InputDecoration(
                labelText: '密码',
              ),
              obscureText: true,
            ),
            SizedBox(height: 16.0),
            ElevatedButton(
              child: Text('登录'),
              onPressed: () => _login(context),
            ),
          ],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';
import 'package:your_app/login_page.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      initialRoute: '/',
      routes: {
        '/': (context) => LoginPage(),
        '/home': (context) => HomePage(),
      },
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: Text('Welcome!'),
      ),
    );
  }
}