如何在flutter中实现sqflite的延迟加载

dependencies:
  sqflite: ^2.0.0

import 'package:sqflite/sqflite.dart';
import 'package:path/path.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 initDatabase();
    return _db!;
  }

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

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

  void _onCreate(Database db, int version) async {
    // 创建数据库表
    await db.execute('CREATE TABLE IF NOT EXISTS your_table_name (id INTEGER PRIMARY KEY, name TEXT)');
  }

  // 延迟加载数据
  Future<List<Map<String, dynamic>>> fetchItems() async {
    Database database = await db;
    return await database.query('your_table_name');
  }
}

import 'package:flutter/material.dart';
import 'package:path/path.dart' as path;
import 'database_helper.dart';

class YourPage extends StatefulWidget {
  @override
  _YourPageState createState() => _YourPageState();
}

class _YourPageState extends State<YourPage> {
  DatabaseHelper databaseHelper = DatabaseHelper();
  List<Map<String, dynamic>> items = [];

  @override
  void initState() {
    super.initState();
    fetchItems();
  }

  void fetchItems() async {
    List<Map<String, dynamic>> fetchedItems = await databaseHelper.fetchItems();
    setState(() {
      items = fetchedItems;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Your Page'),
      ),
      body: ListView.builder(
        itemCount: items.length,
        itemBuilder: (context, index) {
          return ListTile(
            title: Text(items[index]['name']),
          );
        },
      ),
    );
  }
}