Swift Timer not working properly for old iPhone models - swift

Question

I am getting a problem with Swift timer. Timer are not working properly for old iPhone models like iPhone 6. When I printed out time, timer counts every 2 second as 1 second. But if i change withTimeInterval as 0.05, it works a bit better. But still is not work as real life time. Here is my code. Can anyone help me ?
weak var timer: Timer?
var startTime : TimeInterval!
var elapsingTime: Double = 0.0
func configureTimer(totalSecond: Double) {
startTime = Date().timeIntervalSinceReferenceDate
self.invalidateTimer()
DispatchQueue.main.async {
self.timer = Timer.scheduledTimer(timeInterval: 0.02,target: self,selector: #selector(self.advanceTimer(timer:)),userInfo: nil,repeats: true)
}
}
#objc func advanceTimer(timer: Timer) {
elapsingTime += 0.02
self.questionView.configureProgressBar(totalTime: Double(self.totalSecond), elapsingTime: elapsingTime)
self.isTimeExpired = false
self.elapsingTime = Date().timeIntervalSinceReferenceDate - self.startTime
if Int(elapsingTime) == Int(totalSecond) {
self.timer!.invalidate()
self.isTimeExpired = true
self.userAnswerIndex = -1
self.sendAnswer(index: self.userAnswerIndex, isTimeExpired: self.isTimeExpired)
}
}

Answer 1

Timers are not very precise. There precisions is about 0.05 seconds I think. And if a process require a lot of power, your timer will be even more slowed down. The solution can be to save the time when you start your timer and that each time your timer fire, you do a mathematical operation to know how many time passed :
class YourClass {
var startTime : TimeInterval!
//...
func configureTimer() {
startTime = Date().timeIntervalSinceReferenceDate //You add this line
elapsingTime = 0.0
timer?.invalidate()
DispatchQueue.main.async {
self.timer = Timer.scheduledTimer(withTimeInterval: 0.01, repeats: true, block: { [weak self] timer in
guard let self = self else { return }
self.elapsingTime = Date().timeIntervalSinceReferenceDate - self.startTime //You change this one
self.questionView.configureProgressBar(totalTime: self.totalTime, elapsingTime: self.elapsingTime)
self.questionView.videoQuestionPlayer.player?.play()
if Int(self.elapsingTime) == Int(self.totalTime) {
self.timer!.invalidate()
self.isTimeExpired = true
self.sendAnswer(index: -1)
}
})
}
}
}

Answer 2

I would try setting it up like this.
var myTimer = Timer()
var counter = 0.0
myTimer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(yourTargetFunctionHere), userInfo: nil, repeats: true)
#objc func yourTargetFunctionHere() {
//in here is where you do all your code work
counter += 0.1
if counter == yourElapsedTime {
//when your target time is hit do something here
}
if counter == finishedTime {
self.timer.invalidate()
self.counter = 0
}
}