如何在flutter的背景上设置自定义声音通知？

dependencies:
  flutter_local_notifications: ^5.0.0

import 'package:flutter_local_notifications/flutter_local_notifications.dart';

class NotificationManager {
  FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin;

  // 初始化通知插件
  Future<void> init() async {
    flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
    const AndroidInitializationSettings initializationSettingsAndroid =
        AndroidInitializationSettings('app_icon');
    final InitializationSettings initializationSettings =
        InitializationSettings(
            android: initializationSettingsAndroid);
    await flutterLocalNotificationsPlugin.initialize(initializationSettings);
  }

  // 设置自定义声音通知
  Future<void> setCustomSoundNotification() async {
    const AndroidNotificationDetails androidPlatformChannelSpecifics =
        AndroidNotificationDetails(
      'channel_id',
      'channel_name',
      'channel_description',
      sound: RawResourceAndroidNotificationSound('custom_sound'),
    );
    const NotificationDetails platformChannelSpecifics =
        NotificationDetails(android: androidPlatformChannelSpecifics);
    await flutterLocalNotificationsPlugin.show(
      0,
      'Notification Title',
      'Notification Body',
      platformChannelSpecifics,
    );
  }
}

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

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  final NotificationManager notificationManager = NotificationManager();
  await notificationManager.init();
  await notificationManager.setCustomSoundNotification();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Custom Sound Notification',
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Custom Sound Notification'),
        ),
        body: const Center(
          child: Text('Custom Sound Notification Example'),
        ),
      ),
    );
  }
}