Create a stopwatch in Swift using .timeIntervalSince()-CodePudding

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.

CodePudding user response：

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:)

CodePudding user response：

//
//  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)
        
    }
}