FCM background notifications not working in iOS

I have a problem with FCM notification on iOS.

I receive notifications with success when my app is in foreground (the callback didReceiveRemoteNotification in appdelegate is fired), but I don't receive notifications when the app is in background (I do not see anything in the notification tray of iOS).

So, I think the problem is in the format of the message sent by FCM. The json sent by my server to FCM, is in the following format:

{  
   "data":{  
      "title":"mytitle",
      "body":"mybody",
      "url":"myurl"
   },
   "notification":{  
      "title":"mytitle",
      "body":"mybody"
   },
   "to":"/topics/topic"
}

As you can see, there are two blocks in my json: one notification block (to receive notifications in background), and one data block (to receive notifications in foreground).

I cannot understand why notifications in background are not received. My doubts are about the order of the blocks (is a problem if I put the "data" block before the "notification" block?).

EDIT: More info about the problem.

This is my appdelegate.swift:

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate
{
    var window: UIWindow?


    // Application started
    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject : AnyObject]?) -> Bool
    {
        let pushNotificationSettings: UIUserNotificationSettings = UIUserNotificationSettings(forTypes: [.Alert, .Badge, .Sound], categories: nil)
        application.registerUserNotificationSettings(pushNotificationSettings)
        application.registerForRemoteNotifications()

        FIRApp.configure()

        NSNotificationCenter.defaultCenter().addObserver(self, selector: "tokenRefreshNotification:", name: kFIRInstanceIDTokenRefreshNotification, object: nil)

        return true
    }




    // Handle refresh notification token
    func tokenRefreshNotification(notification: NSNotification) {
        let refreshedToken = FIRInstanceID.instanceID().token()
        print("InstanceID token: \(refreshedToken)")

        // Connect to FCM since connection may have failed when attempted before having a token.
        if (refreshedToken != nil)
        {
            connectToFcm()

            FIRMessaging.messaging().subscribeToTopic("/topics/topic")
        }

    }


    // Connect to FCM
    func connectToFcm() {
        FIRMessaging.messaging().connectWithCompletion { (error) in
            if (error != nil) {
                print("Unable to connect with FCM. \(error)")
            } else {
                print("Connected to FCM.")
            }
        }
    }


    // Handle notification when the application is in foreground
    func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject], fetchCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) {
            // If you are receiving a notification message while your app is in the background,
            // this callback will not be fired till the user taps on the notification launching the application.
            // TODO: Handle data of notification

            // Print message ID.
            print("Message ID: \(userInfo["gcm.message_id"])")

            // Print full message.
            print("%@", userInfo)
    }


    // Application will enter in background
    func applicationWillResignActive(application: UIApplication)
    {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
    }



    // Application entered in background
    func applicationDidEnterBackground(application: UIApplication)
    {
        FIRMessaging.messaging().disconnect()
        print("Disconnected from FCM.")
    }



    // Application will enter in foreground
    func applicationWillEnterForeground(application: UIApplication)
    {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }



    // Application entered in foreground
    func applicationDidBecomeActive(application: UIApplication)
    {
        connectToFcm()

        application.applicationIconBadgeNumber = 0;
    }



    // Application will terminate
    func applicationWillTerminate(application: UIApplication)
    {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }


}

The only way I can receive messages in foreground, is by disabling method swizzling, setting FirebaseAppDelegateProxyEnabled to NO in my info.plist.

In this case, FCM documentation says that I have to implement in my appdelegate.swift two methods:

 - FIRMessaging.messaging().appDidReceiveMessage(userInfo)  in didReceiveRemoteNotification callback
 - FIRInstanceID.instanceID().setAPNSToken(deviceToken, type: FIRInstanceIDAPNSTokenType.Sandbox) in didRegisterForRemoteNotificationsWithDeviceToken callback

But if I implement those functions, messages stops to arrive even when the app is in foreground.

I know this is very strange.

EDIT 2:

When the app is in background the notification isn't received, but when i open my app, the same notification is received immediately (method didReceiveRemoteNotification is fired).

Assuming you've set up everything correctly, then setting the priority of the message from normal to high should make it appear immediately. This is due to the way iOS bundles notifications and handles them. You can read about the Priority of FCM notifications here. Please note that you shouldn't really use high in production unless there is a good case for it, as it has a battery penalty.

Here is the reference from Apple's docs

The priority of the notification. Specify one of the following values:

10–Send the push message immediately. Notifications with this priority must trigger an alert, sound, or badge on the target device. It is an error to use this priority for a push notification that contains only the content-available key.

5—Send the push message at a time that takes into account power considerations for the device. Notifications with this priority might be grouped and delivered in bursts. They are throttled, and in some cases are not delivered. If you omit this header, the APNs server sets the priority to 10.

You need to set the content_available property to true like so:

{  
   "data":{  
      "title":"mytitle",
      "body":"mybody",
      "url":"myurl"
   },
   "notification":{  
      "title":"mytitle",
      "body":"mybody",
      "content_available": true
   },
   "to":"/topics/topic"
}

There is a blue note box on in this section that states this: https://firebase.google.com/docs/cloud-messaging/concept-options#notifications

Priority and content_available (as mentioned in other answers) are the key elements to make sure you receive the notifications. Tests showed interesting results, so I thought to share them here.

Test Results: Swift 3, Xcode 8, iOS 10

Priority = "high" => "immediate" (within obvious network delays) reception of message.

Priority = "normal" => various results (generally fast, though obviously slower than "high")

content_available = true in the notifications (no payload message)

Foreground = data received as expected
Background = data received as expected (when opening the app)

content_available = true in the top level (no payload message)

Foreground = data received as expected
Background = data received as expected (when opening the app)

content_available = true in the notifications (with message {title/body})

Foreground = data received TWICE
Background = data received TWICE (when opening the app)

content_available = true in the top level (with payload message)

Foreground = data received TWICE
Background = data received TWICE (when opening the app)

CONCLUSIONS:

While Priority is a possible cause of not receiving messages, the MOST IMPORTANT factor is that you must have either 'content_available' or a payload message.
content_available MUST be used on data-only payloads (without it, no message is ever sent).
content_available SHOULD NOT be used on payloads that contain messages as it causes double messages to be sent from FCM.
No difference found in the use of content_available in the top level or in the notifications.

EDIT: Additional testing results: - if you have a msg title you MUST have a msg body or you don't get an alert.

The odd part of this is that you WILL get the vibrate, badge and sound, but the alert box won't show up unless you have a body as well as the title.

You might need to add the push notification entitlement. Do this by going to your target settings, then clicking "Capabilities" and turning "Push Notifications" on.

Target Capabilities

when you use direct FCM channel messages you can not receive notification in background

this is a paragraph from Firebase document:

With the direct channel enabled, the FCM backend uses a reliable message queue to keep track of pending messages when the app is in the background or closed. When the app goes to the foreground and the connection is re-established, the channel will automatically send pending messages to the client until it gets an acknowledgement from the client.

you can use FCM APNs interface to receive notifications in both foreground and background

FCM background notifications not working in iOS

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