App Timer in the background

The system will typically suspend your app shortly after the user moves it to the background [1] [2]. At that point timers start to behave oddly [3]. There’s typically two ways to deal with this:

• If you don’t need to notify the user when the timer expires, you can cancel the timer as you go into the background and then set it back up again when you come back to the foreground.

• If you do need to notify the user, you should use the UserNotifications framework to schedule a notification for the alarm time. If your app is in the foreground, you can catch this notification and display your own custom UI. If your app is in background, the system will display the notification for you.

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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

[1] Unless you have some specific reason to continue running in the background, for example, you’re an audio playback app.

[2] Oh, and this doesn’t happen if you’re attached with the Xcode debugger, so you need to test this stuff by launching your app from the Home screen.

[3] There’s a bunch of complexity here based on exactly how the timer is scheduled and exactly what happens once you’re in the background.

Is there anything else we can do like leveraging the Location Services we ask for?

could we in theory have my timer running, run a check to see if the timer is going and prevent the app from going to sleep?

You have two basic paths to a solution here:

• You can accept that your app will be suspended, and possibly terminated, while it’s in the background (A).

• You can try to keep your app running in the background (B).

IMO, option A is the best option because:

• Option B requires you to use a background execution mode that will let you run continually in the background. Such modes exist — for example, the audio background moded I referenced in my previous post — but they always have significant technical limitations.

• Even if you get past those technical limitations, you still have to worry about App Review. They are very up front about the specific scrutiny that they apply to apps using these background modes (see clause 2.5.4 of the [App Store Review Guidelines][ASRG].

• Once your timer fires, you then have to figure out how to play sound from the background, which can be a challenge.

• Even if you manage to get this working, you still end up with an app that’s sitting in the background consuming memory and power without any great user benefit.

You can spend your time trying to get around these issues if you like, but you’d be better off using that time to dig into option A.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"