如何用sqflite flutter实现搜索委托

dependencies:
  sqflite: ^2.0.0+3

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

class DatabaseHelper {
  static final DatabaseHelper _instance = 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 {
    String databasesPath = await getDatabasesPath();
    String path = join(databasesPath, 'my_database.db');

    return await openDatabase(
      path,
      version: 1,
      onCreate: (Database db, int version) async {
        // 创建表的操作
        await db.execute(
          'CREATE TABLE IF NOT EXISTS contacts (id INTEGER PRIMARY KEY, name TEXT, email TEXT)',
        );
      },
    );
  }

  // 添加数据的方法
  Future<int> insertContact(Contact contact) async {
    Database? db = await database;
    return await db!.insert('contacts', contact.toMap());
  }

  // 搜索数据的方法
  Future<List<Contact>> searchContacts(String query) async {
    Database? db = await database;
    List<Map<String, dynamic>> maps = await db!.query(
      'contacts',
      where: 'name LIKE ? OR email LIKE ?',
      whereArgs: ['%$query%', '%$query%'],
    );

    return List.generate(maps.length, (i) {
      return Contact(
        id: maps[i]['id'],
        name: maps[i]['name'],
        email: maps[i]['email'],
      );
    });
  }
}

class Contact {
  final int? id;
  final String name;
  final String email;

  Contact({this.id, required this.name, required this.email});

  Map<String, dynamic> toMap() {
    return {
      'id': id,
      'name': name,
      'email': email,
    };
  }
}

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

class SearchPage extends StatefulWidget {
  @override
  _SearchPageState createState() => _SearchPageState();
}

class _SearchPageState extends State<SearchPage> {
  final TextEditingController _searchController = TextEditingController();
  List<Contact> _searchResults = [];

  void _searchContacts(String query) async {
    DatabaseHelper databaseHelper = DatabaseHelper();
    List<Contact> results = await databaseHelper.searchContacts(query);

    setState(() {
      _searchResults = results;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Search'),
      ),
      body: Column(
        children: [
          TextField(
            controller: _searchController,
            onChanged: _searchContacts,
            decoration: InputDecoration(
              labelText: 'Search',
            ),
          ),
          Expanded(
            child: ListView.builder(
              itemCount: _searchResults.length,
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text(_searchResults[index].name),
                  subtitle: Text(_searchResults[index].email),
                );
              },
            ),
          ),
        ],
      ),
    );
  }
}