Can I make network calls within my iOS background fetch? - ios

Question

I am currently trying to create notifications when a user has new messages. I'm trying to do this with local notifications because I'm very much a beginner and it seems(?) easier than push notifications. My question is, can I check my Firebase database during my background fetch?
What I've experienced is that the background fetch function works- but only before my app memory has been suspended, thus negating the point of the background fetch. I run it, I simulate a background fetch, but unless the app was just open, it does nothing and tells me "Warning: Application delegate received call to -application:performFetchWithCompletionHandler: but the completion handler was never called."
Here's my code if it's useful. I know it probably seems like a funky way to go about this.
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
//Firebase
FirebaseApp.configure()
//there was other firebase stuff here that I don't think is relevant to this question
UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { (didAllow, error) in
}
UIApplication.shared.setMinimumBackgroundFetchInterval(UIApplicationBackgroundFetchIntervalMinimum)
return true
}
func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: #escaping (UIBackgroundFetchResult) -> Void) {
myDatabase.child("users").child(userID!).child("hasNewMessages").observeSingleEvent(of: .value) { (snapshot) in
if snapshot.value as! Bool == true {
let content = UNMutableNotificationContent()
content.title = "You have unread messages"
content.badge = 1
let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
let request = UNNotificationRequest(identifier: "testing", content: content, trigger: trigger)
UNUserNotificationCenter.current().add(request, withCompletionHandler: nil)
}
}
}

Answer 1

It is probably better to look at using push notifications as then your user's don't have to wait until iOS decides to invoke your background fetch; they can be notified of new messages immediately.
However, your problem is as described by the message you see in the console; you need to invoke the completionHandler that was passed to the background fetch method when you have finished your background operation to let iOS know what happened. It uses this information to tune how often and when your background fetch method is called.
func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: #escaping (UIBackgroundFetchResult) -> Void) {
myDatabase.child("users").child(userID!).child("hasNewMessages").observeSingleEvent(of: .value) { (snapshot) in
if snapshot.value as! Bool == true {
let content = UNMutableNotificationContent()
content.title = "You have unread messages"
content.badge = 1
let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
let request = UNNotificationRequest(identifier: "testing", content: content, trigger: trigger)
UNUserNotificationCenter.current().add(request, withCompletionHandler: nil)
}
completionHandler(.newData)
}
}