Create a stopwatch in Swift using .timeIntervalSince()

user_18847408 0
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I need to create a simple stopwatch in Swift using the method timeIntervalSince(). I don't really understand how to use timeIntervalSince (what I need and how to implement it) and how to transform it into a String that will show me the passed time like "00:00:00".

I know I need to use a Timer to update the Label and invalidate it when clicking on "Stop".

I'd really appreciate any help on this. Let me know if you need more information.

stopwatch swift xcode
2 Answers

The method timeIntervalSince(_:) is a method of Date. It gives you the number of seconds that have passes since some other date and the date you are asking.

So,

Create a StopwatchVC. Give StopwatchVC a startTime var of type Date. Also give it a Timer var. Lets call that updateTimer.

When the user taps the start button, save Date() (the time right now) into startTime. Also start a repeating timer, updateTimer that fires every 1/10 second. (or however often you want to update your stopwatch, but note that faster than 1/60 is pointless because the screen can't update any faster than that, and timers are only accurate to about 1/50 sec anyway.)

Each time updateTimer fires, calculate the number of seconds that have elapsed since the start time and display it to the screen:

let seconds = Date().timeIntervalSince(startTime)

Date() is the current date and time, with sub-millisecond accuracy. Date().timeIntervalSince(startTime) will give you the number of seconds since startTime, again with sub-millisecond accuracy.

Format and display the elapsed time to the screen. You could use a DateComponentsFormatter or build a time string yourself using a NumberFormatter, or even String(format:)

user_2051850 
//
//  StopWatchVC.swift
//  Gem
//
//  Created by Macbook 5 on 4/18/22.
//

import UIKit

class StopWatchVC:UIViewController {
    
    var timer:Timer?
    var startTime = Date()
    let titleLabel = UILabel()
   
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(titleLabel)
        titleLabel.frame = CGRect(x: 0, y: 0, width: 200, height: 60)
        titleLabel.center = view.center
        titleLabel.textColor = .red
        view.backgroundColor = .white
        timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: (#selector(updateTimer)), userInfo: nil, repeats: true)
    }
    
    @objc func updateTimer() {
        let timeInterval =  Date().timeIntervalSince(startTime)
        titleLabel.text = timeInterval.stringFromTimeInterval()
    }
}
extension TimeInterval{
    
    func stringFromTimeInterval() -> String {
        
        let time = NSInteger(self)
        
        let ms = Int((self.truncatingRemainder(dividingBy: 1)) * 1000)
        let seconds = time % 60
        let minutes = (time / 60) % 60
        let hours = (time / 3600)
        
        return String(format: "%0.2d:%0.2d:%0.2d.%0.3d",hours,minutes,seconds,ms)
        
    }
}
user_142602410
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