flutter-samples/packages/stream_chat_v1/lib/notifications_service.dart

import 'package:flutter_local_notifications/flutter_local_notifications.dart'
    hide Message;
import 'package:stream_chat_flutter/stream_chat_flutter.dart';

void showLocalNotification(Event event, String currentUserId) async {
  if (![
        EventType.messageNew,
        EventType.notificationMessageNew,
      ].contains(event.type) ||
      event.user!.id == currentUserId) {
    return;
  }
  if (event.message == null) return;
  final flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
  final initializationSettingsAndroid =
      AndroidInitializationSettings('launch_background');
  final initializationSettingsIOS = IOSInitializationSettings();
  final initializationSettings = InitializationSettings(
    android: initializationSettingsAndroid,
    iOS: initializationSettingsIOS,
  );
  await flutterLocalNotificationsPlugin.initialize(initializationSettings);
  await flutterLocalNotificationsPlugin.show(
    event.message!.id.hashCode,
    event.message!.user!.name,
    event.message!.text,
    NotificationDetails(
      android: AndroidNotificationDetails(
        'message channel',
        'Message channel',
        'Channel used for showing messages',
        priority: Priority.high,
        importance: Importance.high,
      ),
      iOS: IOSNotificationDetails(),
    ),
  );
}