How to run timer for two dates subtraction in Swift

Question

*I have two dates. Those, I have to do date format in UTC and after that have to do subtraction of two dates. I have to run timer for remaining time. And once its reaches 0 second, I have to stop timer and I have to call some api.

fromDate: 2021-07-21T09:04:38.306Z, toDate: 2021-07-21T09:06:08.000Z

    override func viewDidLoad() {
        super.viewDidLoad()

let when = DispatchTime.now() + 0.1 // change 2 to desired number of seconds
                    DispatchQueue.main.asyncAfter(deadline: when) {
                        self.countDownTimer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(MyViewController.countDownTime), userInfo: nil, repeats: true)
                    }

}

  @objc func countDownTime() {
        
        let unlockDuration = self.getCountDownTime(currentTime: "2021-07-21T09:04:38.306Z" , unlockTime: "2021-07-21T09:06:08.000Z")
        if unlockDuration == "0d :0h : 0: 0" {
            self.stopTimer()
        }
    }
    
    func stopTimer(){
            guard self.countDownTimer != nil else {
                fatalError("No timer active, start the timer before you stop it.")
            }
            self.countDownTimer?.invalidate()
            self.callAPI()
        }

  func getCountDownTime(currentTime: String, unLockTime: String) -> String {
        
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ssZ"
        dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
        let unlockDate = dateFormatter.date(from: "\(unlockTime)") ?? Date()
        let currentDate = dateFormatter.date(from: "\(currentTime)") ??  Date()
        print(currentDate)
        print(unlockDate)
        let calendar = Calendar.current
        let diffDateComponents = calendar.dateComponents([.day, .hour, .minute, .second], from: unlockDate, to: currentDate)
        let countdown = "\(String(describing:diffDateComponents.day!))d :\(String(describing: diffDateComponents.hour!))h : \(String(describing: diffDateComponents.minute!)): \(String(describing: diffDateComponents.second!))"

        print(countdown)
        return countdown
        
    }

func callAPI() {
//Calling api here
}

But, Always its printing as 0d :0h : 0: 0 And its not showing seconds, minutes Its printing like below always

2021-07-21 11:14:23 +0000
2021-07-21 11:14:23 +0000
0d :0h : 0: 0

Any Suggestions?*

Clearly `dateFormatter.date(from:)` is returning nil. Try changing our `dateFormatter.dateFormat` to "`yyyy-MM-dd'T'HH:mm:ss.SSSZ`" — CSmith, Jul 21 '21 at 11:34
I tried with above suggested format by you @CSmith, BUT STILL SHOWING like 2021-07-21 11:36:47 +0000, 2021-07-21 11:36:47 +0000, 0d :0h : 0: 0 in console — Anilkumar iOS - ReactNative, Jul 21 '21 at 11:37
I bet you'll find that `dateFormatter.date(from: "\(unlockTime)")` is returing nil. — CSmith, Jul 21 '21 at 11:40
No, its returning date dateFormatter.date(from: "\(unlockTime)") — Anilkumar iOS - ReactNative, Jul 21 '21 at 11:41
the log output in your question clearly shows otherwise, i.e. that its printing `Date()` for both `currentDate` and `unlockDate` — CSmith, Jul 21 '21 at 11:44
The corrected format string suggested by @CSmith worked for me — Paulw11, Jul 21 '21 at 11:47
@CSmith that format is working fine now to me which was suggested by you, But, its not decrementing the time. Always printing 0d :0h : -1: -29 till infinity — Anilkumar iOS - ReactNative, Jul 21 '21 at 11:48
@AnilkumariOS-ReactNative You're printing the difference between two fixed dates, why it should decrementing? — Mikhail Vasilev, Jul 21 '21 at 12:01

score 1 · Answer 1 · answered Jul 21 '21 at 11:49

1

To parse a date with this format:

2021-07-21T09:04:38.306Z

use

dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"

Your are getting a difference of 0 because dateFormatter.date(from: "\(unlockTime)") is returning nil, so your subtracting Date() from Date() and getting a 0 difference.

answered Jul 21 '21 at 11:49

CSmith

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format is working fine now to me which was suggested by you, But, its not decrementing the time for each second. Always printing 0d :0h : -1: -29 till infinity – Anilkumar iOS - ReactNative Jul 21 '21 at 11:57
determining the time difference between two Date() is a widely answered problem (see https://stackoverflow.com/questions/4371757/how-can-i-calculate-the-difference-between-two-dates). Its not clear to me what you're actually trying to do but now that your `dateFormat` is fixed I'm sure you'll figure it out. – CSmith Jul 21 '21 at 12:10
Also, don’t forget to set the `locale` for the date formatter to `Locale(identifier: "en_US_POSIX")` – Rob Jul 21 '21 at 14:10

How to run timer for two dates subtraction in Swift

1 Answers1