Firebase notification not receiving in background for iOS 17 in flutter

In iOS, when an app is terminated (i.e., not running in the background), it cannot receive notifications directly. However, you can still handle notifications that were delivered while the app was running in the background or terminated by using the userNotificationCenter(_:didReceive:withCompletionHandler:) method of the UNUserNotificationCenterDelegate.

Here’s how you can handle notifications in Flutter when the app is terminated in iOS:

Set up the UNUserNotificationCenterDelegate in your AppDelegate.swift file:

import UIKit
import Flutter
import UserNotifications

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate, UNUserNotificationCenterDelegate {
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        GeneratedPluginRegistrant.register(with: self)

        // Set UNUserNotificationCenterDelegate
        UNUserNotificationCenter.current().delegate = self

        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }

    // Handle notification when app is in foreground, background, or terminated
    func userNotificationCenter(
        _ center: UNUserNotificationCenter,
        didReceive response: UNNotificationResponse,
        withCompletionHandler completionHandler: @escaping () -> Void
    ) {
        // Handle notification here
        completionHandler()
    }
}

2.Implement the handle method in your main.dart file to handle notifications received when the app is in the background or terminated:

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
import 'package:firebase_messaging/firebase_messaging.dart';

final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
    FlutterLocalNotificationsPlugin();

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await initializeFlutterLocalNotificationsPlugin();

  runApp(MyApp());
}

Future<void> initializeFlutterLocalNotificationsPlugin() async {
  const AndroidInitializationSettings initializationSettingsAndroid =
      AndroidInitializationSettings('@mipmap/ic_launcher');
  final InitializationSettings initializationSettings =
      InitializationSettings(android: initializationSettingsAndroid);
  await flutterLocalNotificationsPlugin.initialize(initializationSettings);
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final FirebaseMessaging _firebaseMessaging = FirebaseMessaging.instance;

  @override
  void initState() {
    super.initState();
    _firebaseMessaging.requestPermission();
    _firebaseMessaging.getToken().then((token) {
      print('FCM Token: $token');
    });

    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      print("onMessage: $message");
      // Handle notification received while app is in foreground
    });

    FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
      print("onMessageOpenedApp: $message");
      // Handle notification tapped when app is in background or terminated
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Demo'),
      ),
      body: Center(
        child: Text(
          'Push Notifications',
        ),
      ),
    );
  }
}

With this setup, you can handle notifications received while the app is running in the background or terminated. When the app is terminated, the userNotificationCenter(_:didReceive:withCompletionHandler:) method of the UNUserNotificationCenterDelegate will be called, and you can handle the notification accordingly.