简单的Flutter sqflite登录->写入数据库->导航->从数据库流中检索

dependencies:
  flutter:
    sdk: flutter
  sqflite: ^2.0.0+4

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

class DatabaseHelper {
  static final DatabaseHelper _instance = new DatabaseHelper._internal();
  factory DatabaseHelper() => _instance;
  static Database? _database;

  Future<Database> get database async {
    if (_database != null) return _database!;
    _database = await _initDatabase();
    return _database!;
  }

  DatabaseHelper._internal();

  Future<Database> _initDatabase() async {
    return openDatabase(
      'user_database.db',
      version: 1,
      onCreate: _onCreate,
    );
  }

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

Future<void> addUser(String username, String password) async {
  final db = await DatabaseHelper().database;
  await db.insert(
    'user',
    {'username': username, 'password': password},
  );
}

Future<bool> loginUser(String username, String password) async {
  final db = await DatabaseHelper().database;
  final List<Map<String, dynamic>> users = await db.query('user');
  for (var user in users) {
    if (user['username'] == username && user['password'] == password) {
      return true;
    }
  }
  return false;
}

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Sqflite Demo')),
        body: LoginScreen(),
      ),
    );
  }
}

class LoginScreen extends StatefulWidget {
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  final _formKey = GlobalKey<FormState>();
  String _username = '';
  String _password = '';

  Future<void> _submitForm() async {
    if (_formKey.currentState!.validate()) {
      bool isLoggedIn = await loginUser(_username, _password);
      if (isLoggedIn) {
        Navigator.push(
          context,
          MaterialPageRoute(builder: (context) => HomeScreen()),
        );
      } else {
        ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(content: Text('Invalid login')),
        );
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Form(
      key: _formKey,
      child: Column(
        children: [
          TextFormField(
            decoration: InputDecoration(labelText: 'Username'),
            validator: (value) {
              if (value!.isEmpty) return 'Please enter username';
              return null;
            },
            onSaved: (value) => _username = value!,
          ),
          TextFormField(
            decoration: InputDecoration(labelText: 'Password'),
            obscureText: true,
            validator: (value) {
              if (value!.isEmpty) return 'Please enter password';
              return null;
            },
            onSaved: (value) => _password = value!,
          ),
          ElevatedButton(
            onPressed: _submitForm,
            child: Text('Login'),
          ),
        ],
      ),
    );
  }
}

class HomeScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Home')),
      body: Center(
        child: FutureBuilder<bool>(
          future: loginUser('admin', 'admin'),
          builder: (context, AsyncSnapshot<bool> snapshot) {
            if (snapshot.connectionState == ConnectionState.waiting) {
              return CircularProgressIndicator();
            } else if (snapshot.hasError) {
              return Text('Error: ${snapshot.error}');
            } else {
              return Text(snapshot.data! ? 'Logged In' : 'Not Logged In');
            }
          },
        ),
      ),
    );
  }
}