Timer issue presenting time

Question

I am trying to update the label with the current Time.

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var label: UILabel!
    let date = Date()

    override func viewDidLoad() {
        super.viewDidLoad()

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


    func updateTime(){

        label.text = DateFormatter.localizedString(from: Date(), dateStyle: .none, timeStyle: .long)

    }


}

when I am using at updateTime() label.text = DateFormatter.localizedString(from: Date(), dateStyle: .none, timeStyle: .long) I am getting the result that I want

When I am using label.text = DateFormatter.localizedString(from: date, dateStyle: .none, timeStyle: .long)

the timer is not working. can someone please explain me ? ?

From my understanding I if I use a date and not Date() then I need a timer/counter to count and calculate. If so any suggestions ?

Thanks a lot

P

Answer 1

In your second example, date is a constant value. So even though updateTime() is called every second, it is setting the label to the same value every time.

From the comments, it seems you want to be able to advance a constant time when the timer is running.

To count up from an arbitrary constant Date, store a start time when the timer is started. Use that to compute the interval the timer has been running, and then use that interval to advance date:

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var label: UILabel!
    let date = Date()
    var start: Date?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Save the time when the timer starts 
        start = Date()

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


    func updateTime(){

        // compute how long the timer has been running
        let interval = Date().timeIntervalSince(start!)

        // compute new date based on how long the timer has been running
        let newDate = date.addingTimeInterval(interval)
        label.text = DateFormatter.localizedString(from: newDate, dateStyle: .none, timeStyle: .long)

    }
}

The timer firing is not very accurate, and you might see your counting pause for a second and then jump 2 seconds. If you make your timer interval something smaller, like 0.1 for instance, you can avoid a visual glitch.