I have an app that does a countdown with a Timer. The countdown tracks multiple steps (all at the same intervals) as well as the total time left, and updates 2 separate UILabels accordingly. Occasionally, the labels will be out of sync.
I can't say for sure, but I think it might be only happening when I pause the countdown sometimes, and usually on steps later than the first step. It's most apparent on the last step when the two labels should be displaying the same exact thing, but will sometimes be 1 second off.
The other tricky thing is that sometimes pausing and resuming after the time has gone out of sync will get it back in sync.
My guess is I'm getting something weird happening in the pause code and/or the moving between steps, or maybe the calculating and formatting of TimeIntervals. Also I'm using rounded() on the calculated TimeIntervals because I noticed only updating the timer every 1s the labels would freeze and skip seconds a lot. But I'm unsure if that's the best way to solve this problem.
Here's the relevant code. (still need to work on refactoring but hopefully it's easy to follow, I'm still a beginner)
#IBAction func playPauseTapped(_ sender: Any) {
if timerState == .running {
//pause timer
pauseAnimation()
timer.invalidate()
timerState = .paused
pausedTime = Date()
playPauseButton.setImage(UIImage(systemName: "play.circle"), for: .normal)
} else if timerState == .paused {
//resume paused timer
guard let pause = pausedTime else { return }
let pausedInterval = Date().timeIntervalSince(pause)
startTime = startTime?.addingTimeInterval(pausedInterval)
endTime = endTime?.addingTimeInterval(pausedInterval)
currentStepEndTime = currentStepEndTime?.addingTimeInterval(pausedInterval)
pausedTime = nil
startTimer()
resumeAnimation()
timerState = .running
playPauseButton.setImage(UIImage(systemName: "pause.circle"), for: .normal)
} else {
//first run of brand new timer
startTimer()
startProgressBar()
startTime = Date()
if let totalTime = totalTime {
endTime = startTime?.addingTimeInterval(totalTime)
}
currentStepEndTime = Date().addingTimeInterval(recipeInterval)
timerState = .running
playPauseButton.setImage(UIImage(systemName: "pause.circle"), for: .normal)
currentWater += recipeWater[recipeIndex]
currentWeightLabel.text = "\(currentWater)g"
}
}
func startTimer() {
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(runTimer), userInfo: nil, repeats: true)
}
#objc func runTimer() {
let currentTime = Date()
guard let totalTimeLeft = endTime?.timeIntervalSince(currentTime).rounded() else { return }
guard let currentInterval = currentStepEndTime?.timeIntervalSince(currentTime).rounded() else { return }
//end of current step
if currentInterval <= 0 {
//check if end of recipe
if recipeIndex < recipeWater.count - 1 {
//move to next step
totalTimeLabel.text = totalTimeLeft.stringFromTimeInterval()
currentStepEndTime = Date().addingTimeInterval(recipeInterval)
startProgressBar()
currentStepTimeLabel.text = recipeInterval.stringFromTimeInterval()
stepsTime += recipeInterval
recipeIndex += 1
//update some ui
} else {
//last step
currentStepTimeLabel.text = "00:00"
totalTimeLabel.text = "00:00"
timer.invalidate()
//alert controller saying finished
}
} else {
//update time labels
currentStepTimeLabel.text = currentInterval.stringFromTimeInterval()
totalTimeLabel.text = totalTimeLeft.stringFromTimeInterval()
}
}
extension TimeInterval {
func stringFromTimeInterval() -> String {
let time = NSInteger(self)
let seconds = time % 60
let minutes = (time / 60) % 60
return String(format: "%0.2d:%0.2d",minutes,seconds)
}
}
EDIT UPDATE: I tried a few different things but still kept having the same issue. I started testing with printing the TimeInterval and the formatted string to compare and see what's off. It's definitely some sort of rounding error.
Total - 173.50678288936615 / 02:54
Step - 39.00026595592499 / 00:39
Total - 172.5073879957199 / 02:53
Step - 38.00087106227875 / 00:38
Total - 171.1903439760208 / 02:51
Step - 36.68382704257965 / 00:37
Total - 170.19031596183777 / 02:50
Step - 35.683799028396606 / 00:36
As you can see, the total time skips from 2:53 to 2:51, but the step timer remains consistent. The reason is the TimeInterval for total goes from 172.5 which gets rounded up, to 171.19 which gets rounded down.
I've also watched the timer count down without touching pause, and it remains in sync reliably. So I've narrowed it down to my pause code.
Fixed my issue and posting here for posterity. I ended up making my totalTimeLeft and currentInterval global properties. Then, on pause and resume, instead of tracking the paused time and adding it to endTime, I just used the totalTimeLeft and currentInterval values that are still stored from the last Timer firing and doing endTime = Date().addingTimeInterval(totalTimeLeft) and the same with the interval time. This got rid of the paused time adding weird amounts that would mess up the rounding.
Related
I'm still pretty new to coding and Swift. So bear with me.
Problem Statement : I've got a stopwatch style app that has two concurrent timers start at the same time and display in a mm:ss.SS format, but one is designed to reset to 0 at specific intervals automatically while the other keeps going and tracks total time.
Similar to a "lap" function but it does it automatically. The problem I've encountered is that occasionally the timers aren't perfectly synced up when the user pauses the timers. Since the reset happens at an exact second, both timers should have identical hundredths of a second, while the seconds and minutes will obviously be different. But sometimes the hundredths will be off by .01 or more.
Now, I know Timer isn't designed to be perfectly accurate, and in practice on my app this isn't even a huge deal. My timer doesn't even need to be accurate to the hundredth of a second, and while running it's not noticeably off at all, only while paused. I could display fewer decimal places or none at all, but I prefer the style of showing the hundredths since it fits in well with the stock timer app style.
So if there's a way to make this work, I'd like to keep it.
Screenshot : screenshot
What I tried :
#IBAction func playPauseTapped(_ sender: Any) {
if timerState == .new {
//start new timer
startCurrentTimer()
startTotalTimer()
currentStartTime = Date.timeIntervalSinceReferenceDate
totalStartTime = Date.timeIntervalSinceReferenceDate
timerState = .running
//some ui updates
} else if timerState == .running {
//pause timer
totalTimer.invalidate()
currentTimer.invalidate()
timerState = .paused
pausedTime = Date()
//other ui updates
} else if timerState == .paused {
//resume paused timer
let pausedInterval = Date().timeIntervalSince(pausedTime!)
pausedIntervals.append(pausedInterval)
pausedIntervalsCurrent.append(pausedInterval)
pausedTime = nil
startCurrentTimer()
startTotalTimer()
timerState = .running
//other ui updates
}
}
func startTotalTimer() {
totalTimer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(runTotalTimer), userInfo: nil, repeats: true)
}
func startCurrentTimer() {
currentTimer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(runCurrentTimer), userInfo: nil, repeats: true)
}
func resetCurrentTimer() {
currentTimer.invalidate()
currentStartTime = Date.timeIntervalSinceReferenceDate
pausedIntervalsCurrent.removeAll()
startCurrentTimer()
}
#objc func runCurrentTimer() {
let currentTime = Date.timeIntervalSinceReferenceDate
//calculate total paused time
var pausedSeconds = pausedIntervalsCurrent.reduce(0) { $0 + $1 }
if let pausedTime = pausedTime {
pausedSeconds += Date().timeIntervalSince(pausedTime)
}
let currentElapsedTime: TimeInterval = currentTime - currentStartTime - pausedSeconds
currentStepTimeLabel.text = format(time: currentElapsedTime)
if currentElapsedTime >= recipeInterval {
if recipeIndex < recipeTime.count - 1 {
recipeIndex += 1
//ui updates
//reset timer to 0
resetCurrentTimer()
} else {
//last step
currentTimer.invalidate()
}
}
}
#objc func runTotalTimer() {
let currentTime = Date.timeIntervalSinceReferenceDate
//calculate total paused time
var pausedSeconds = pausedIntervals.reduce(0) { $0 + $1 }
if let pausedTime = pausedTime {
pausedSeconds += Date().timeIntervalSince(pausedTime)
}
let totalElapsedTime: TimeInterval = currentTime - totalStartTime - pausedSeconds
totalTimeLabel.text = format(time: totalElapsedTime)
if totalElapsedTime >= recipeTotalTime {
totalTimer.invalidate()
currentTimer.invalidate()
//ui updates
}
}
func format(time: TimeInterval) -> String {
//formats TimeInterval into mm:ss.SS
let formater = DateFormatter()
formater.dateFormat = "mm:ss.SS"
let date = Date(timeIntervalSinceReferenceDate: time)
return formater.string(from: date)
}
You should use a single timer. And when you need a reset to zero, save the current time to a variable.
When presenting the time in the UI, calculate the difference between the running total timer, and the time you saved previously.
I try to implement simple player with UISlider to indicate at what time is current audio file.
In code I have added two observers:
slider.rx.value.subscribe(onNext: { value in
let totalTime = Float(CMTimeGetSeconds(self.player.currentItem!.duration))
let seconds = value * totalTime
let time = CMTime(seconds: Double(seconds), preferredTimescale: CMTimeScale(NSEC_PER_SEC))
self.player.seek(to: time)
}).disposed(by: bag)
let interval = CMTime(seconds: 0.1, preferredTimescale: CMTimeScale(NSEC_PER_SEC))
player.addPeriodicTimeObserver(forInterval: interval, queue: nil) { [weak self] time in
self?.updateSlider(with: time)
}
with one private function:
private func updateSlider(with time: CMTime) {
let currentTime = CMTimeGetSeconds(time)
var totalTime = CMTimeGetSeconds(player.currentItem!.duration)
if totalTime.isNaN {
totalTime = 0
}
startLabel.text = Int(currentTime).descriptiveDuration
endLabel.text = Int(totalTime).descriptiveDuration
slider.value = Float(currentTime / totalTime)
}
When audio plays, everything is fine and slider is pretty much updated. The problem occurs when I try to move slider manually while audio is playing, then it jumps. Why?
UPDATE:
I know why actually. Because I update it twice: manually and from player observer, but how to prevent from this behaviour? I have no idea;) please, help.
One simple way to go about this would be to prevent addPeriodicTimeObserver from calling self?.updateSlider(with: time) when the slider is being touched.
This can be determined via the UISliders isTracking property:
isTracking
A Boolean value indicating whether the control is currently tracking
touch events.
While tracking of a touch event is in progress, the control sets the
value of this property to true. When tracking ends or is cancelled for
any reason, it sets this property to false.
Ref: https://developer.apple.com/documentation/uikit/uicontrol/1618210-istracking
This is present in all UIControl elements which you can use in this way:
player.addPeriodicTimeObserver(forInterval: interval, queue: nil) { [weak self] time in
//check if slider is being touched/tracked
guard self?.slider.isTracking == false else { return }
//if slider is not being touched, then update the slider from here
self?.updateSlider(with: time)
}
Generic Example:
#IBOutlet var slider: UISlider!
//...
func startSlider() {
slider.value = 0
slider.maximumValue = 10
Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { [weak self] (timer) in
print("Slider at: \(self?.slider.value)")
guard self?.slider.isTracking == false else { return }
self?.updateSlider(to: self!.slider.value + 0.1)
}
}
private func updateSlider(to value: Float) {
slider.value = value
}
I'm sure there are other (better) ways out there but I haven't done much in RxSwift (yet).
I hope this is good enough for now.
Sorry if this is a newbie question, I am very new to iOS & Swift. I have a problem with the timer interval: I set 0.01 time interval but it doesn't correspond with the timer label, because 0.01 corresponds in one millisecond but it doesn't show it. So basically the timer is skewed.
timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(updateStopwatch) , userInfo: nil, repeats: true)
#IBAction func startStopButton(_ sender: Any) {
buttonTapped()
}
func updateStopwatch() {
milliseconds += 1
if milliseconds == 100 {
seconds += 1
milliseconds = 0
}
if seconds == 60 {
minutes += 1
seconds = 0
}
let millisecondsString = milliseconds > 9 ?"\(milliseconds)" : "0\(milliseconds)"
let secondsString = seconds > 9 ?"\(seconds)" : "0\(seconds)"
let minutesString = minutes > 9 ?"\(minutes)" : "0\(minutes)"
stopWatchString = "\(minutesString):\(secondsString).\(millisecondsString)"
labelTimer.text = stopWatchString
}
func buttonTapped() {
if isTimerRunning {
isTimerRunning = !isTimerRunning
timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(updateStopwatch) , userInfo: nil, repeats: true)
startStopButton.setTitle("Stop", for: .normal)
}else{
isTimerRunning = !isTimerRunning
timer.invalidate()
startStopButton.setTitle("Start", for: .normal)
}
}
Devices have maximum screen update rate (most are 60 fps), so there is no point in going faster than that. For maximum screen refresh rate, use a CADisplayLink rather than a Timer, which is coordinated perfectly for screen refreshes (not only in frequency, but also the timing within the screen refresh cycle).
Also don't try to keep track of the time elapsed by adding some value (because you are not guaranteed that it will be called with the desired frequency). Instead, before you start your timer/displaylink, save the start time and then when the timer/displaylink is called, display the elapsed time in the desired format.
For example:
var startTime: CFTimeInterval!
weak var displayLink: CADisplayLink?
func startDisplayLink() {
self.displayLink?.invalidate() // stop prior display link, if any
startTime = CACurrentMediaTime()
let displayLink = CADisplayLink(target: self, selector: #selector(handleDisplayLink(_:)))
displayLink.add(to: .current, forMode: .commonModes)
self.displayLink = displayLink
}
func handleDisplayLink(_ displayLink: CADisplayLink) {
let elapsed = CACurrentMediaTime() - startTime
let minutes = Int(elapsed / 60)
let seconds = elapsed - CFTimeInterval(minutes) * 60
let string = String(format: "%02d:%05.2f", minutes, seconds)
labelTimer.text = string
}
func stopDisplayLink() {
displayLink?.invalidate()
}
Note, CACurrentMediaTime() uses mach_time, like hotpaw2 correctly suggested, but does the conversion to seconds for you.
The time delay of a scheduledTimer is only approximate, and can differ from what is requested by many milliseconds, due to iOS overhead. A repeating Timer is even worse for timing, as any delay jitter errors will accumulate. So don't use a Timer for timing longer events.
A CADisplayLink is a more reliable timer, as it is synchronized to the 60 Hz display refresh (e.g. this is the maximum rate that any UILabel can be changed on devices other than the latest iPad Pros). There is no use trying to update a time display any faster (except possibly on the latest iPad Pros).
Also, do not use Date methods for timing, as they are not guaranteed to be monotonic when the device is connected to a network (as NTP can change the clock time right in the middle of your timing activity).
You should check any elapsed time measurement UI against one of the built-in timers such as mach_time. mach_absolute_time() is guaranteed to be monotonic, and not affected by NTP or other network activity.
I have built a basic app with a stopwatch on it. It runs off 3 buttons - play, pause, and reset on a navigation bar which write to a label called timerLabel.
The trouble is as soon as the app is closed or the iPhone goes into sleep mode the stopwatch stops. I've looked for the answer in other questions and it seems that the only way around it is to record the actual time when the app goes off and record the time when it reawakens and compare the difference - then write this to the label
Trouble is I have absolutely no idea how to incorporate that into my current code. I don't even know how to get the time. Here is my code from my view controller.
func updateTimer() {
time++
updateTimeDisplay()
}
func secondsToHoursMinutesSeconds (seconds : Int) -> (Int, Int, Int) {
let h = seconds / 3600
let m = (seconds % 3600) / 60
let s = (seconds % 60)
return (h, m, s)
}
func pauseTimer() {
timer.invalidate()
}
func startTimer() {
if !timer.valid {
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("updateTimer"), userInfo: nil, repeats: true) }
else {
print("The Stopwatch has already started!")
}
}
func resetTimer() {
time = 0
timer.invalidate()
updateTimeDisplay()
}
func updateTimeDisplay() {
let (h, m, s) = secondsToHoursMinutesSeconds(time)
let timeToDisplay = String(format:"%02d:%02d:%02d", h, m, s)
timerLabel.text = timeToDisplay
}
You cannot use an NSTimer in the background, and your app will not run for long there anyway.
When the application enters background, you should stop the timer and take a note of the current time. Then when the application resumes again you should restart the timer, and calculate how long the app was in the background to update the display accordingly.
I'm working on a timer app for iPhone. But when switching views and coming back to initial timer view,
the label is not updated. While I can see it's still running in the print log.
I have the code below in my viewDidLoad.
How can I start refreshing the label again when I enter the timer view again?
The other view is handled through Segue.
func updateTime() {
var currentTime = NSDate.timeIntervalSinceReferenceDate()
//Find the difference between current time and start time.
var elapsedTime: NSTimeInterval = currentTime - startTime
//calculate the minutes in elapsed time.
let minutes = UInt8(elapsedTime / 60.0)
elapsedTime -= (NSTimeInterval(minutes) * 60)
//calculate the seconds in elapsed time.
let seconds = UInt8(elapsedTime)
elapsedTime -= NSTimeInterval(seconds)
//find out the fraction of milliseconds to be displayed.
let fraction = UInt8(elapsedTime * 100)
//add the leading zero for minutes, seconds and millseconds and store them as string constants
let strMinutes = minutes > 9 ? String(minutes):"0" + String(minutes)
let strSeconds = seconds > 9 ? String(seconds):"0" + String(seconds)
println("----------")
println("currentTime")
println (currentTime)
println("elapsedTime")
println (elapsedTime)
println("extraTime")
println (extraTime)
println("summed")
println (summed)
//concatenate minuets, seconds and milliseconds as assign it to the UILabel
displayTimeLabel.text = "\(strMinutes):\(strSeconds)"
}
#IBAction func start(sender: AnyObject) {
if (!timer.valid) {
let aSelector : Selector = "updateTime"
timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: aSelector, userInfo: nil, repeats: true)
startTime = NSDate.timeIntervalSinceReferenceDate()
}
}
#IBAction func stop(sender: AnyObject) {
timer.invalidate()
}
I was having the exact same problem in a tab view application and solved it using the NSNotification Center. To make it work in your case, you could make a separate function just for updating the text.
func updateText(notification: NSNotification) {
displayTimeLabel.text = "\(strMinutes):\(strSeconds)"
}
Then inside your "updateTime" function, where you had the line I took out, replace it with a postNotifiction:
NSNotificationCenter.defaultCenter().postNotificationName("UpdateTimer", object: nil)
Then put the observer inside a ViewDidAppear function in the View Controller where the text should be updated:
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(false)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "updateText:", name: "UpdateTimer", object: nil)
}
With the observer in viewDidAppear, the updateText function always gets called, and the text is updated even when you switch views and come back.