How to be able to receive background notifications with FCM on iOS (android already works)

[GilbertoGmobil]

In my Flutter app the admin users can send notifications to the others users through FCM. In android already works but in iOS the notification arrives only with the app opened. I already tried many things on internet and still don't working.

This is the dart code that manages the pushs:

Future<dynamic> myBackgroundMessageHandler(Map<String, dynamic> message) async {
  if (message.containsKey('data')) {
    // Handle data message
    final dynamic data = message['data'];
  }

  if (message.containsKey('notification')) {
    // Handle notification message
    final dynamic notification = message['notification'];
  }

  // Or do other work.
}


class PushNotificationsManager {

  PushNotificationsManager._();

  factory PushNotificationsManager() => _instance;

  static final PushNotificationsManager _instance = PushNotificationsManager
      ._();

  final FirebaseMessaging _firebaseMessaging = FirebaseMessaging();
  final NotificationPlugin _notificationPlugin = NotificationPlugin();

  Future<void> init() async {
    if (Platform.isIOS) {
      _firebaseMessaging.requestNotificationPermissions(
          IosNotificationSettings());
    }
    _firebaseMessaging.configure(
      // Called when the app is in the foreground and we receive a push notif.
      onMessage: (Map<String, dynamic> message) async {
        print("onMessage: ${message}");
        print(message['notification']['body']);
        _notificationPlugin.showNotification(
            title: 'TEST',
            content: message['notification']['body']
        );
        //sendNotification();
      },
      // Called when the app has been closed completely and its opened
      // from the notification directly

      //onBackgroundMessage: Platform.isAndroid ? myBackgroundMessageHandler:null,
      onBackgroundMessage: myBackgroundMessageHandler,
      onLaunch: (Map<String, dynamic> message) async {
        print("onLaunch: $message");
        if(Platform.isIOS){
          message = _modifyNotificationJson(message);
        }
      },
      // Called when the app is in the background and its opened from the notif
      onResume: (Map<String, dynamic> message) async {
        print("onMessage: ${message}");
        if(Platform.isIOS){
          message = _modifyNotificationJson(message);
        }
      },
    );

  }

  Map _modifyNotificationJson(Map<String, dynamic> message) {
    message['data'] = Map.from(message ?? {});
    message['notification'] = message['aps']['alert'];
    return message;
  }


  Future sendNotification(String body, String title) async {
    final String url = 'https://fcm.googleapis.com/fcm/send';
    var notification;
    notification =
    '{"notification": {"body": "${body}", "title": "${title}", "content_available": "true", "click_action": "FLUTTER_NOTIFICATION_CLICK"}, "priority": "high", "to": "MYTOPIC"}';
    final response = await http.post(
        url,
        headers: <String, String>{
          "Content-Type": "application/json",
          "Keep-Alive": "timeout=5",
          "Authorization": "key=MYKEY"
        },
        body: notification
    );

    print(response.body);
  }
}

AppDelegate.swift:

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    if #available(iOS 10.0, *) {
      UNUserNotificationCenter.current().delegate = self as? UNUserNotificationCenterDelegate
    }
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

I already enabled pushNotifications and background modes in xcode, already check my certificates but the problem stands. Someone could help me?

[RyanMannix]

I have the same issue:
Notification arrives fine, but there's some logic (writing to file) when onBackgroundMessage is called which doesn't happen for iOS (but does for android).

Most of what I've read suggests there are 2 reasons why a onBackgroundMessage won't trigger from background:

1. it's a data message, only RemoteMessage type will trigger it.
2. content-available value must be set to true.
   And additional note: if you need to modify the message after receiving it- that isn't supported.

We are sending the notification to FCM via the firebase_admin golang SDK like so:

app := appcontext.GetInstance()
ctx := app.Context
client, err := app.App.Messaging(ctx)
if err != nil {
	log.Fatalf("error getting Messaging client: %v\n", err)
}

message := &messaging.MulticastMessage{
	Notification: &messaging.Notification{
		Title: n.Title,
		Body:  n.Body,
	},

	Data: n.Payload,

	Android: &messaging.AndroidConfig{
		Notification: &messaging.AndroidNotification{
			ChannelID: "high_importance_channel",
			Priority:  messaging.PriorityHigh,
		},
	},

	APNS: &messaging.APNSConfig{
		Payload: &messaging.APNSPayload{
			Aps: &messaging.Aps{
				Sound:            "default",
				ContentAvailable: true,
			},
		},
	},

	Tokens: n.FcmTokens,
}

Thinking the message doesn't contain a required value, but can't seem to figure it out.