Swift 3: Programming a simple stopwatch

For the last while, I have been extending my programming skill set by learning Swift. Swift is a programming language for MacOS, iOS, watchOS and tvOS applications. As both a resource for myself and hopefully a resource for fellow programmers, I thought I might start publishing some of my early scratchings. I emphasise early! Don’t expect the entire source code to an Uber app… yet.

The following code creates a simple stopwatch/timer. It could be easily extended to include advanced functionality like reverse timers, alarms, notifications, etc. I learnt a lot from this so I hope it may be useful to your Swift journey. I would love any feedback so feel free to comment.

I used the following very helpful sources when researching how I should approach this Swift snippet:

• http://stackoverflow.com/questions/35809723/swift-pause-and-resume-nstimer
• http://rshankar.com/simple-stopwatch-app-in-swift/

I separated the three time blocks (min/sec/ms) into separate labels as I found that putting them all into one label made for a shaky viewing experience. I suspect by having them separate will allow for easy design enhancements.

//
//  ViewController.swift
//  Simple Stopwatch
//
//  Created by Mike Little on 2/03/17.
//  Copyright © 2017 Creative Digital. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

weak var timer: Timer?
var startTime: Double = 0
var time: Double = 0
var elapsed: Double = 0
var status: Bool = false

@IBOutlet weak var labelMinute: UILabel!
@IBOutlet weak var labelSecond: UILabel!
@IBOutlet weak var labelMillisecond: UILabel!
@IBOutlet weak var resetBtn: UIButton!

override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.

// No point enabling reset until stopwatch actually started
resetBtn.isEnabled = false

}

override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}

@IBAction func toggleStartStop(_ sender: UIButton!) {

// If button status is true use stop function, relabel button and enable reset button
if (status) {
stop()
sender.setTitle("START", for: .normal)
resetBtn.isEnabled = true

// If button status is false use start function, relabel button and disable reset button
} else {
start()
sender.setTitle("STOP", for: .normal)
resetBtn.isEnabled = false
}

}

@IBAction func resetBtn(_ sender: Any) {

// Invalidate timer
timer?.invalidate()

// Reset timer variables
startTime = 0
time = 0
elapsed = 0
status = false

// Reset all three labels to 00
let strReset = String("00")
labelMinute.text = strReset
labelSecond.text = strReset
labelMillisecond.text = strReset

}

func start() {

startTime = Date().timeIntervalSinceReferenceDate - elapsed
timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(updateCounter), userInfo: nil, repeats: true)

// Set Start/Stop button to true
status = true

}

func stop() {

elapsed = Date().timeIntervalSinceReferenceDate - startTime
timer?.invalidate()

// Set Start/Stop button to false
status = false

}

func updateCounter() {

// Calculate total time since timer started in seconds
time = Date().timeIntervalSinceReferenceDate - startTime

// Calculate minutes
let minutes = UInt8(time / 60.0)
time -= (TimeInterval(minutes) * 60)

// Calculate seconds
let seconds = UInt8(time)
time -= TimeInterval(seconds)

// Calculate milliseconds
let milliseconds = UInt8(time * 100)

// Format time vars with leading zero
let strMinutes = String(format: "%02d", minutes)
let strSeconds = String(format: "%02d", seconds)
let strMilliseconds = String(format: "%02d", milliseconds)

// Add time vars to relevant labels
labelMinute.text = strMinutes
labelSecond.text = strSeconds
labelMillisecond.text = strMilliseconds

}
}