Maybe my Google-fu is lacking or there’s not much about this on the web: how do you separate handling local notifications when the app is in foreground from when it is in background? After all you’ll probably want to show a specific view when the user taps a notification badge. Here’s one way to do it.

When you schedule UILocalNotifications for a future time and when the user is using the app at that moment, application(_, didReceiveLocalNotification:) gets called – the same AppDelegate callback that’ll be invoked when the user taps on a notification badge while your app is in background mode. I found that surprisingly inconvenient.

The only notification the app I’m working on receives is a reminder. When the user taps the badge, the app activates and the event details should appear. When the app is in foreground already, nothing should happen. The user should not be magically taken to the event detaila view while she’s doing something elss. How weird would that be?

So we need a toggle to ignore the notification when the app is open already.

func application(application: UIApplication, 
                 didReceiveLocalNotification notification: UILocalNotification) {
    guard !isActive else { return }
    handleLocalNotification(localNotification)
}

Where does the isActive toggle gets set, though?

A naive approach is to set it to false when the app goes into background mode. Only the app comes into foreground and then handles the notification when you interact with the badge, so that’s not a good fit. Active/inactive callbacks work better since applicationDidBecomeActive(_) is called last, for whatever reason.

var isActive = true

func applicationDidBecomeActive(application: UIApplication) {
    isActive = true
}

func applicationWillResignActive(application: UIApplication) {
    isActive = false
}

This works as expected and we’re set.

Only then did I discover UIApplicationState. We can get rid of all the toggle-related code and write this instead:

func application(application: UIApplication, 
                 didReceiveLocalNotification notification: UILocalNotification) {
    guard application.applicationState == .Inactive else { return }
    handleLocalNotification(localNotification)
}

Sheesh.