title: ios 10 Firebase Push Notification delegate method not called in background mode
body: <p>I have been struggling with this problem for days and I have looked at every post about this and nothing works.</p>
  
  <p>I am using FCM (Firebase Cloud Messaging). FCM talks directly to the app when in foreground, but it will use APNS when the app is in background.</p>
  
  <p>I am trying to call a method everytime the app got notification by calling the method in the push notification's delegate function</p>
  
  <p>I have these 2 delegate functions:
  <code>func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -&gt; Void)
  </code>
  and
  <code>
  func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -&gt; Void)
  </code>
  which does not get called in background, according to apple documentation.</p>
  
  <p>I also have this function which I believe should get called in the background but it does not.
  <code>func application(_ application: UIApplication,didReceiveRemoteNotification userInfo: [AnyHashable: Any],fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -&gt; Void)</code></p>
  
  <p>I have all of these functions in ViewController</p>
  
  <p>In background mode, I get banner notifications, but none of the delegate is called. Is there any way to make any of them work in the background, if not what should I do?
  In addition I also get this error : <code>&lt;FIRMessaging/WARNING&gt; FIRMessaging receiving notification in invalid state 2</code> in the log everytime I send a payload while the app is in the background.</p>
  
  <p>Here is the payload that I send using postmate:</p>
  
  <p><code>
  {
      "priority":"high",
      "notification":{
          "sound": "default",
          "badge": "1",
          "title":"mytitle",
          "body":"mybody",
          "message":"Hello"
      },
     "content_available":true,
     "to" : "/topics/myTopic"
  }
  </code>
  I already turned on push notification in capabilities and checked push notification in background modes under capabilities.</p>
  
  <p>I use Xcode 8 and have been testing on iphone 6 iOS 10.0.2</p>