didReceiveRemoteNotification not working in the background

Implementing didReceiveRemoteNotification and didReceiveRemoteNotification:fetchCompletionHandler is the correct way, but you also need to do the following:

Make sure to register for remote notifications, see documentation here:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{    
    [[UIApplication sharedApplication] registerForRemoteNotificationTypes:(UIRemoteNotificationTypeAlert | UIRemoteNotificationTypeBadge | UIRemoteNotificationTypeSound)];

    return YES;
}

Also make sure to edit Info.plist and check the "Enable Background Modes" and "Remote notifications" check boxes:

Additionally, you need to add "content-available":1 to your push notification payload, otherwise the app won't be woken if it's in the background (see documentation here updated):

For a push notification to trigger a download operation, the notification’s payload must include the content-available key with its value set to 1. When that key is present, the system wakes the app in the background (or launches it into the background) and calls the app delegate’s application:didReceiveRemoteNotification:fetchCompletionHandler: method. Your implementation of that method should download the relevant content and integrate it into your app

So payload should at least look like this:

{
    aps = {
        "content-available" : 1,
        sound : ""
    };
}

I had the same problem. Notification banner appeared, but -application:didReceiveRemoteNotification:fetchCompletionHandler: method was not called. The solution for me that worked was to add implementation of - application:didReceiveRemoteNotification: method and forward call to -application:didReceiveRemoteNotification:fetchCompletionHandler::

func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject]) {

    self.application(application, didReceiveRemoteNotification: userInfo) { (UIBackgroundFetchResult) in

    }
}

1. Register for push notification in app delegate.
2. Add background mode in app capabilities.
3. Add "content-available"="1" while sending the push notification(if you are using firebase replace "content-available"="1" by "content_available"="true" while sending the push notification from server side).