Timer Stops When Phone Goes Into Airplane Mode, Won't Restart After Leaving AM - ios

Question

OK. Looked through the possible answers, but I don't see my issue here.
I have a fairly bog-standard GCD repeating timer:
class RepeatingGCDTimer {
/// This holds our current run state.
private var state: _State = ._suspended
/// This is the time between fires, in seconds.
let timeInterval: TimeInterval
/// This is the callback event handler we registered.
var eventHandler: (() -> Void)?
/* ############################################################## */
/**
This calculated property will create a new timer that repeats.
It uses the current queue.
*/
private lazy var timer: DispatchSourceTimer = {
let t = DispatchSource.makeTimerSource() // We make a generic, default timer source. No frou-frou.
t.schedule(deadline: .now() + self.timeInterval, repeating: self.timeInterval) // We tell it to repeat at our interval.
t.setEventHandler(handler: { [unowned self] in // This is the callback.
self.eventHandler?() // This just calls the event handler we registered.
})
return t
}()
/// This is used to hold state flags for internal use.
private enum _State {
/// The timer is currently paused.
case _suspended
/// The timer has been resumed, and is firing.
case _resumed
}
/* ############################################################## */
/**
Default constructor
- parameter timeInterval: The time (in seconds) between fires.
*/
init(timeInterval inTimeInterval: TimeInterval) {
self.timeInterval = inTimeInterval
}
/* ############################################################## */
/**
If the timer is not currently running, we resume. If running, nothing happens.
*/
func resume() {
if self.state == ._resumed {
return
}
self.state = ._resumed
self.timer.resume()
}
/* ############################################################## */
/**
If the timer is currently running, we suspend. If not running, nothing happens.
*/
func suspend() {
if self.state == ._suspended {
return
}
self.state = ._suspended
self.timer.suspend()
}
/* ############################################################## */
/**
We have to carefully dismantle this, as we can end up with crashes if we don't clean up properly.
*/
deinit {
self.timer.setEventHandler {}
self.timer.cancel()
self.resume() // You need to call resume after canceling. I guess it lets the queue clean up.
self.eventHandler = nil
}
}
Works great!
...except when it doesn't.
That would be when I put the device into Airplane Mode.
At that point, the timer stops firing.
Even when I come out of Airplane Mode, the timer doesn't restart.
The app uses UIApplication.shared.isIdleTimerDisabled = true/false to keep the app awake, but that doesn't seem to keep the events coming.
Can anyone clue me into what's happening here, and how I might be able to work around it?
This app needs to work in Airplane Mode. In fact, it is most likely to be used in Airplane Mode.

Answer 1

OK. I think I solved this. As is often the case with these things, it's PEBCAK.
I have a routine that stops the timer when the app is backgrounded, and failed to put in a corresponding restart for when it is foregrounded.
When I slide up the Control Center, it backgrounds the app.
My bad.
Yeah, it's embarrassing, but I want to leave this question here as a warning to others.