Displaying Live Time Label in Swift 4?

Question

My time label is displaying the time, when I open my app but it won't update it live. I had a look at other answers but they didn't make sense.

// CURRENT TIME

    @IBOutlet weak var currentTimeLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        getCurrentTime()
    }

// FORMAT TIME

func getCurrentTime(){
        let formatter = DateFormatter()
        formatter.dateFormat = "hh:mm"
        let str = formatter.string(from: Date())
        currentTimeLabel.text = str
    }

I want my app to update the time label live. Thanks in advance. It's probably a really simple fix.

score 3 · Answer 1 · answered Dec 23 '18 at 11:04

Use Timer for your requirement,

class ViewController: UIViewController {
    @IBOutlet weak var currentTimeLabel: UILabel!

    var timer = Timer()

    override func viewDidLoad() {
        super.viewDidLoad()
        getCurrentTime()
    }

    private func getCurrentTime() {
        timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector:#selector(self.currentTime) , userInfo: nil, repeats: true)
    }

    @objc func currentTime() {
        let formatter = DateFormatter()
        formatter.dateFormat = "hh:mm"
        currentTimeLabel.text = formatter.string(from: Date())
    }
}

Robert Dresler · Accepted Answer · 2018-12-23T11:24:23.387

2

You can create Timer with repeating every minute (because you don't need seconds for anything) starting in the next minute (so call getCurrentTime() once before you start Timer).

Every minute code inside timer's closure gets executed so you can say that you want to call getCurrentTime(). Now your currentTimeLabel will be updated every minute

let now = Date()
let date = Calendar.current.date(bySettingHour: Calendar.current.component(.hour, from: now), minute: Calendar.current.component(.minute, from: now) + 1, second: 0, of: now)!
let timer = Timer(fire: date, timeInterval: 60, repeats: true) { _ in
    self.getCurrentTime()
}

Also I would recommend you to have formatter variable outside of the method (in global scope)

lazy var formatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateFormat = "hh:mm" // or "hh:mm a" if you need to have am or pm symbols
    return formatter
}()

and then in getCurrentTime() just get String and change text of currentTimeLabel

func getCurrentTime() {
    currentTimeLabel.text = formatter.string(from: Date())
}

edited Dec 23 '18 at 11:24

answered Dec 23 '18 at 10:44

Robert Dresler

10,580
2
22
40

If OP’s method has to be called every second, it would be better to have the date formatter initialization outside of the method. Better resource-wise. – Eric Aya Dec 23 '18 at 10:46
Thanks. Stupid question but where would I add this code? – J.Kearney Dec 23 '18 at 10:48
@J.Kearney where you want to start Timer. So for example to `viewDidLoad` – Robert Dresler Dec 23 '18 at 10:49
@RobertDresler yes viewDidLoad. – J.Kearney Dec 23 '18 at 10:50
note that hh is for 01-12. It is missing the am/pm notation. the correct would be `"h:mm a"` or for 24h clock `"HH:mm" ` – Leo Dabus Dec 23 '18 at 11:09
@RobertDresler Worked! Thanks heaps mate – J.Kearney Dec 23 '18 at 11:10
Btw You should use timeStyle instead of a fixed time format. That should be defined by the user settings/locale. – Leo Dabus Dec 23 '18 at 11:10
Also why would you repeat the timer 60 times per second if the minute changes only every 60 seconds? – Leo Dabus Dec 23 '18 at 11:16
@LeoDabus because when timer starts in let's say 12:16:05 then next update will be in 12:17:05 – Robert Dresler Dec 23 '18 at 11:16
You can use fireAt and make it start the next even second – Leo Dabus Dec 23 '18 at 11:16
`func activateTimer() { let now = Date() let date = Calendar.current.date(bySettingHour: Calendar.current.component(.hour, from: now), minute: Calendar.current.component(.minute, from: now) + 1, second: 0, of: now)! timer = Timer(fireAt: date, interval: 60, target: self, selector: #selector(updateTime), userInfo: nil, repeats: true) RunLoop.main.add(timer, forMode: .common) }` – Leo Dabus Dec 23 '18 at 11:18
this way the timer will be synced with the device' s clock – Leo Dabus Dec 23 '18 at 11:21
timeInterval: 60 – Leo Dabus Dec 23 '18 at 11:24
@LeoDabus is `RunLoop.main.add(timer, forMode: .common) }` necessarily? – Robert Dresler Dec 23 '18 at 11:24
I don't think so in your code as it is (using the trailing closure). If it works without it you don't need kkk – Leo Dabus Dec 23 '18 at 11:25
This will save a lot of battery. – Leo Dabus Dec 23 '18 at 11:26
1

@LeoDabus okay. Thank you so much! Your advices move me forward! :-) – Robert Dresler Dec 23 '18 at 11:27
you are welcome. dont forget to update the time on view did load otherwise it might take a long time to display it at first – Leo Dabus Dec 23 '18 at 11:29
@LeoDabus I think I wrote it into brackets – Robert Dresler Dec 23 '18 at 11:30
Regarding the common mode it its always a good idea to add the timer to the common mode because allows it to fire in all modes. The timer might not fire under certain circumstances which would look like the clock/timer it is not working. This is more evident when coding for macOS and the user clicks the file menu. https://stackoverflow.com/a/27997548/2303865 – Leo Dabus Dec 23 '18 at 11:36
1

@LeoDabus yes, I'm using it for example when I need to scroll `UITableView` and I also need cells be updated in every time period. – Robert Dresler Dec 23 '18 at 11:46

Displaying Live Time Label in Swift 4?

2 Answers2