How Do I Manage Scheduled Events in Swift 4? - swift

Question

Looking for some direction on how to best manage scheduled events in swift 4 (either external library or Apple support).
I would like to be able to put a task (with a timer) in to some kind of hub that will then execute the task once the timer has run down and then perform the task's completion block at the end of the task.
Can I do this with NSNotification?
Anyone know of a good example app (e.g. GitHub) that I can download and play with to learn how to schedule tasks.
More detail
I am creating timers like this
timer_iosActionsRefresh = Timer(fireAt: date, interval: timeInterval, target: self, selector: #selector(refreshIosActions), userInfo: nil, repeats: true)
RunLoop.main.add( timer_iosActionsRefresh!, forMode: RunLoopMode.commonModes)
I then do this to stop timers
if timer_iosActionsRefresh != nil {
timer_iosActionsRefresh?.invalidate()
timer_iosActionsRefresh = nil
}
This works great in app foregoround mode but does not work in background mode since Apple only supports special states for background mode activities (e.g. CLLocationManager didEnterRegion)
1) Is it possible to create something like a Timer but that will still execute in background mode? Not looking to do heavy or continuous work, just small background queries.
2) Even if there is some way around Timers not working in background mode, will that code make it through Apple app review?

Answer 1

I would recomment using GCD (Grand Central Dispatch), which is fairly easy:
let queue = DispatchQueue.global(qos: .background) // or some higher QOS level
// Do somthing after 10.5 seconds
queue.asyncAfter(deadline: .now() + 10.5) {
// your task code here
DispatchQueue.main.async {
// maybe update UI here after task has finished
}
}
If you dont need a background queue and want to perform the task simply in the main thread, just do:
DispatchQueue.main.asyncAfter(deadline: .now() + 10.5) {
// task etc.
}
If you want to be able to cancel tasks you sheduled, you should take a look at NSOperation (which ist based on GCD and allows cancelling and other higher level stuff).

Answer 2

If I am understanding this question correctly, I would first add the observer to the view controller that you want to run the task's completion block
NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("runCompletionBlock"), object: nil)
then in the method you called from the NSNotification you add the completion block.
then create a timer in the class of the hub you want to make
var timer = Timer()
initialise it
timer = Timer.scheduledTimer(timeInterval: 5, target: self, selector: #selector(runTimedCode), userInfo: nil, repeats: true)
Then create a method runTimedCode() that gets called when the timer finishes.
You can then add a NSNotification to notify the observer you created with
NotificationCenter.default.post(name: Notification.Name("runCompletionBlock"), object: nil)
Not sure if this is what you were after, but it may help.