iOS How to create countdown time [hours,minutes,seccond] Swift 4

Question

I want create countdown time, but i can not find such information how i can do this.

For example i have 200 minutes it's 3,3 hours.

For this 3,3 hours i want make count down timer, and this information can i see at the label?

How i can do this?

I found such code at the forum:

func startTimer() {

    let releaseDateString = "03:33:00"
    let releaseDateFormatter = DateFormatter()
    releaseDateFormatter.dateFormat = "HH:mm:ss"
    releaseDate = releaseDateFormatter.date(from: releaseDateString)! as NSDate

    countdownTimer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(updateTime), userInfo: nil, repeats: true)
}

@objc func updateTime() {

    let currentDate = Date()
    let calendar = Calendar.current

    let diffDateComponents = calendar.dateComponents([.hour, .minute, .second], from: currentDate, to: releaseDate! as Date)

    let countdown = "Hours \(diffDateComponents.hour ?? 0), Minutes \(diffDateComponents.minute ?? 0), Seconds \(diffDateComponents.second ?? 0)"
    label.text = "\(countdown)"

    print(countdown)
}

But i got such result:

Hours -163779, Minutes -48, Seconds -34

Answer 1

Step back for a moment and think about the problem. Updating the UI on a regular bases is actually pretty simply, but it's also unreliable (it only guarantees "at least" precision), so you can't rely on it to accurately update counters or time based values (ie, you shouldn't use it to increment a "second" value on each tick).

What you want is an "anchor" time from which you can calculate the total amount of running time and then calculate the remaining time.

Swift/Apple provides a number of neat APIs which you can use to accomplish all these things.

This is just something I threw together in a Playground...

import UIKit

// Anchor time
let startTime: Date = Date()
// The total amount of time to wait
let duration: TimeInterval = 200 * 60 // 200 minutes

let formatter = DateComponentsFormatter()
formatter.allowedUnits = [.hour, .minute, .second]
formatter.zeroFormattingBehavior = .dropLeading
formatter.unitsStyle = .short
// The amount of time which has past since we started
var runningTime: TimeInterval = 0

// This is just so I can atrificially update the time
var time: Date = Date()
let cal: Calendar = Calendar.current
repeat {
    // Simulate the passing of time, by the minute
    // If this was been called from a timer, then you'd
    // simply use the current time
    time = cal.date(byAdding: .minute, value: 1, to: time)!

    // How long have we been running for?
    runningTime = time.timeIntervalSince(startTime)
    // Have we run out of time?
    if runningTime < duration {
        // Print the amount of time remaining
        print(formatter.string(from: duration - runningTime)!)
    }
} while runningTime < duration

This will print out...

3 hr, 18 min, 59 sec
3 hr, 17 min, 59 sec
3 hr, 16 min, 59 sec
3 hr, 15 min, 59 sec
3 hr, 14 min, 59 sec
3 hr, 13 min, 59 sec
3 hr, 12 min, 59 sec
3 hr, 11 min, 59 sec
3 hr, 10 min, 59 sec
3 hr, 9 min, 59 sec
3 hr, 8 min, 59 sec
3 hr, 7 min, 59 sec
3 hr, 6 min, 59 sec
3 hr, 5 min, 59 sec
3 hr, 4 min, 59 sec
3 hr, 3 min, 59 sec
3 hr, 2 min, 59 sec
3 hr, 1 min, 59 sec
3 hr, 0 min, 59 sec
2 hr, 59 min, 59 sec
2 hr, 58 min, 59 sec
2 hr, 57 min, 59 sec
2 hr, 56 min, 59 sec
2 hr, 55 min, 59 sec
2 hr, 54 min, 59 sec
2 hr, 53 min, 59 sec
2 hr, 52 min, 59 sec
2 hr, 51 min, 59 sec
2 hr, 50 min, 59 sec
2 hr, 49 min, 59 sec
2 hr, 48 min, 59 sec
2 hr, 47 min, 59 sec
2 hr, 46 min, 59 sec
2 hr, 45 min, 59 sec
2 hr, 44 min, 59 sec
2 hr, 43 min, 59 sec
2 hr, 42 min, 59 sec
2 hr, 41 min, 59 sec
2 hr, 40 min, 59 sec
2 hr, 39 min, 59 sec
2 hr, 38 min, 59 sec
2 hr, 37 min, 59 sec
2 hr, 36 min, 59 sec
2 hr, 35 min, 59 sec
2 hr, 34 min, 59 sec
2 hr, 33 min, 59 sec
2 hr, 32 min, 59 sec
2 hr, 31 min, 59 sec
2 hr, 30 min, 59 sec
2 hr, 29 min, 59 sec
2 hr, 28 min, 59 sec
2 hr, 27 min, 59 sec
2 hr, 26 min, 59 sec
2 hr, 25 min, 59 sec
2 hr, 24 min, 59 sec
2 hr, 23 min, 59 sec
2 hr, 22 min, 59 sec
2 hr, 21 min, 59 sec
2 hr, 20 min, 59 sec
2 hr, 19 min, 59 sec
2 hr, 18 min, 59 sec
2 hr, 17 min, 59 sec
2 hr, 16 min, 59 sec
2 hr, 15 min, 59 sec
2 hr, 14 min, 59 sec
2 hr, 13 min, 59 sec
2 hr, 12 min, 59 sec
2 hr, 11 min, 59 sec
2 hr, 10 min, 59 sec
2 hr, 9 min, 59 sec
2 hr, 8 min, 59 sec
2 hr, 7 min, 59 sec
2 hr, 6 min, 59 sec
2 hr, 5 min, 59 sec
2 hr, 4 min, 59 sec
2 hr, 3 min, 59 sec
2 hr, 2 min, 59 sec
2 hr, 1 min, 59 sec
2 hr, 0 min, 59 sec
1 hr, 59 min, 59 sec
1 hr, 58 min, 59 sec
1 hr, 57 min, 59 sec
1 hr, 56 min, 59 sec
1 hr, 55 min, 59 sec
1 hr, 54 min, 59 sec
1 hr, 53 min, 59 sec
1 hr, 52 min, 59 sec
1 hr, 51 min, 59 sec
1 hr, 50 min, 59 sec
1 hr, 49 min, 59 sec
1 hr, 48 min, 59 sec
1 hr, 47 min, 59 sec
1 hr, 46 min, 59 sec
1 hr, 45 min, 59 sec
1 hr, 44 min, 59 sec
1 hr, 43 min, 59 sec
1 hr, 42 min, 59 sec
1 hr, 41 min, 59 sec
1 hr, 40 min, 59 sec
1 hr, 39 min, 59 sec
1 hr, 38 min, 59 sec
1 hr, 37 min, 59 sec
1 hr, 36 min, 59 sec
1 hr, 35 min, 59 sec
1 hr, 34 min, 59 sec
1 hr, 33 min, 59 sec
1 hr, 32 min, 59 sec
1 hr, 31 min, 59 sec
1 hr, 30 min, 59 sec
1 hr, 29 min, 59 sec
1 hr, 28 min, 59 sec
1 hr, 27 min, 59 sec
1 hr, 26 min, 59 sec
1 hr, 25 min, 59 sec
1 hr, 24 min, 59 sec
1 hr, 23 min, 59 sec
1 hr, 22 min, 59 sec
1 hr, 21 min, 59 sec
1 hr, 20 min, 59 sec
1 hr, 19 min, 59 sec
1 hr, 18 min, 59 sec
1 hr, 17 min, 59 sec
1 hr, 16 min, 59 sec
1 hr, 15 min, 59 sec
1 hr, 14 min, 59 sec
1 hr, 13 min, 59 sec
1 hr, 12 min, 59 sec
1 hr, 11 min, 59 sec
1 hr, 10 min, 59 sec
1 hr, 9 min, 59 sec
1 hr, 8 min, 59 sec
1 hr, 7 min, 59 sec
1 hr, 6 min, 59 sec
1 hr, 5 min, 59 sec
1 hr, 4 min, 59 sec
1 hr, 3 min, 59 sec
1 hr, 2 min, 59 sec
1 hr, 1 min, 59 sec
1 hr, 0 min, 59 sec
59 min, 59 sec
58 min, 59 sec
57 min, 59 sec
56 min, 59 sec
55 min, 59 sec
54 min, 59 sec
53 min, 59 sec
52 min, 59 sec
51 min, 59 sec
50 min, 59 sec
49 min, 59 sec
48 min, 59 sec
47 min, 59 sec
46 min, 59 sec
45 min, 59 sec
44 min, 59 sec
43 min, 59 sec
42 min, 59 sec
41 min, 59 sec
40 min, 59 sec
39 min, 59 sec
38 min, 59 sec
37 min, 59 sec
36 min, 59 sec
35 min, 59 sec
34 min, 59 sec
33 min, 59 sec
32 min, 59 sec
31 min, 59 sec
30 min, 59 sec
29 min, 59 sec
28 min, 59 sec
27 min, 59 sec
26 min, 59 sec
25 min, 59 sec
24 min, 59 sec
23 min, 59 sec
22 min, 59 sec
21 min, 59 sec
20 min, 59 sec
19 min, 59 sec
18 min, 59 sec
17 min, 59 sec
16 min, 59 sec
15 min, 59 sec
14 min, 59 sec
13 min, 59 sec
12 min, 59 sec
11 min, 59 sec
10 min, 59 sec
9 min, 59 sec
8 min, 59 sec
7 min, 59 sec
6 min, 59 sec
5 min, 59 sec
4 min, 59 sec
3 min, 59 sec
2 min, 59 sec
1 min, 59 sec
59 sec

The nice thing about DateComponentsFormatter is it's reasonably configurable and makes use of the devices localisation settings to generate its output

You could also look at Stopping timer at defined amount of time in Swift which presents a runnable example of the same concept, but also supports pause/resume capabilities

Answer 2

Use this function for displaying Hours: Minutes: Seconds

func timeString(time: TimeInterval) -> String {
    let hours = Int(time) / 3600
    let minutes = Int(time) / 60 % 60
    let seconds = Int(time) % 60
    return String(format:"%02i:%02i:%02i", hours, minutes, seconds)
}

timerLabel.text = timeString(time: TimeInterval(DurationInSeconds))