Running a timer when the phone is sleeping - ios

Question

I'm building an app and I need a timer to run if the user sends the screen to the background, or if they put the phone in sleep and open it again. I need the timer to still be going.
I tried recording the time when I exit the and enter it again, subtracting the two and adding that to the running count, and it seems to work fine on the Xcode simulator but when I run it on my phone it doesn't work. Any ideas?
Here is the code for reference.
And the timer starts with a button I didn't include that part but it's just a simple IBAction that calls the timer.fire() function.
var time = 0.0
var timer = Timer()
var exitTime : Double = 0
var resumeTime : Double = 0
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(true)
exitTime = Date().timeIntervalSinceNow
}
override func awakeFromNib() {
super.awakeFromNib()
resumeTime = Date().timeIntervalSinceNow
time += (resumeTime-exitTime)
timer.fire()
}
func startTimer() {
if !isTimeRunning {
timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector:
#selector(WorkoutStartedViewController.action), userInfo: nil, repeats: true)
isTimeRunning = true
}
}
func pauseTimer() {
timer.invalidate()
isTimeRunning = false
}
#objc func action()
{
time += 0.1
timerLabel.text = String(time)
let floorCounter = Int(floor(time))
let hour = floorCounter/3600
let minute = (floorCounter % 3600)/60
var minuteString = "\(minute)"
if minute < 10 {
minuteString = "0\(minute)"
}
let second = (floorCounter % 3600) % 60
var secondString = "\(second)"
if second < 10 {
secondString = "0\(second)"
}
if time < 3600.0 {
timerLabel.text = "\(minuteString):\(secondString)"
} else {
timerLabel.text = "\(hour):\(minuteString):\(secondString)"
}
}

Answer 1

You do have the right idea but the first problem I see is that viewWillDissapear is only called when you leave a view controller to go to a new viewController - It is not called when the app leaves the view to enter background (home button press)
I believe the callback functions you are looking for are UIApplication.willResignActive (going to background) and UIApplication.didBecomeActive (app re-opened)
You can access these methods in the AppDelegate or you can set them up on a view controller heres a mix of your code and some changes to produce a working sample on one initial VC:
import UIKit
import CoreData
class ViewController: UIViewController {
#IBOutlet weak var timerLabel: UILabel!
var time = 0.0
var timer = Timer()
var exitTime : Date? // Change to Date
var resumeTime : Date? // Change to Date
var isTimeRunning = false
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
startTimer()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self,
selector: #selector(applicationDidBecomeActive),
name: UIApplication.didBecomeActiveNotification,
object: nil)
// Add willResign observer
NotificationCenter.default.addObserver(self,
selector: #selector(applicationWillResign),
name: UIApplication.willResignActiveNotification,
object: nil)
}
override func viewWillDisappear(_ animated: Bool) {
// Remove becomeActive observer
NotificationCenter.default.removeObserver(self,
name: UIApplication.didBecomeActiveNotification,
object: nil)
// Remove becomeActive observer
NotificationCenter.default.removeObserver(self,
name: UIApplication.willResignActiveNotification,
object: nil)
}
func startTimer() {
if !isTimeRunning {
timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector:
#selector(self.action), userInfo: nil, repeats: true)
isTimeRunning = true
}
}
#objc func action() {
time += 0.1
timerLabel.text = String(time)
let floorCounter = Int(floor(time))
let hour = floorCounter/3600
let minute = (floorCounter % 3600)/60
var minuteString = "\(minute)"
if minute < 10 {
minuteString = "0\(minute)"
}
let second = (floorCounter % 3600) % 60
var secondString = "\(second)"
if second < 10 {
secondString = "0\(second)"
}
if time < 3600.0 {
timerLabel.text = "\(minuteString):\(secondString)"
} else {
timerLabel.text = "\(hour):\(minuteString):\(secondString)"
}
}
#objc func applicationDidBecomeActive() {
// handle event
lookForActiveTimers()
}
func lookForActiveTimers() {
var timers = [NSManagedObject]()
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
return
}
let managedContext = appDelegate.persistentContainer.viewContext
let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Timers")
//3
do {
timers = try managedContext.fetch(fetchRequest)
print("timers: \(timers)")
var activeTimer: NSManagedObject?
for timer in timers {
if let active = timer.value(forKey: "active") as? Bool {
if active {
activeTimer = timer
}
}
}
if let activeTimer = activeTimer {
// Handle active timer (may need to go to a new view)
if let closeDate = activeTimer.value(forKey: "appCloseTime") as? Date {
if let alreadyTimed = activeTimer.value(forKey: "alreadyTimed") as? Double {
let now = Date()
let difference = now.timeIntervalSince(closeDate)
// Handle set up again here
print("App opened with a difference of \(difference) and already ran for a total of \(alreadyTimed) seconds before close")
time = alreadyTimed + difference
startTimer()
}
}
} else {
print("We dont have any active timers")
}
// Remove active timers because we reset them up
for timer in timers {
managedContext.delete(timer)
}
do {
print("deleted")
try managedContext.save() // <- remember to put this :)
} catch {
// Do something... fatalerror
}
} catch let error as NSError {
print("Could not fetch. \(error), \(error.userInfo)")
}
}
#objc func applicationWillResign() {
// handle event
saveActiveTimer()
}
func saveActiveTimer() {
if isTimeRunning {
// Create a new alarm object
guard let appDelegate =
UIApplication.shared.delegate as? AppDelegate else {
return
}
let context = appDelegate.persistentContainer.viewContext
if let entity = NSEntityDescription.entity(forEntityName: "Timers", in: context) {
let newTimer = NSManagedObject(entity: entity, insertInto: context)
newTimer.setValue(true, forKey: "active")
let now = Date()
newTimer.setValue(now, forKey: "appCloseTime")
newTimer.setValue(self.time, forKey: "alreadyTimed")
do {
try context.save()
print("object saved success")
} catch {
print("Failed saving")
}
}
}
}
}
EDIT - Here is the full tested and working code on xCode 11.3 and a physical device iOS 13.2 - You have to figure out how to start and stop the timer according to your buttons - but this example simply starts the timer when the app is first opened and never stops or resets it.
You can reproduce this by creating a new single-view xCode project and replacing the code in the first view controller that it creates for you with the code above. Then create a label to attach to the outlet timerLabel on the VC
Also make sure to enable CoreData in your project while creating your new project * Then set up the entities and attributes in the xcdatamodel file:
Hope this helps