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Miles H.
Miles H.

Reputation: 285

How to stop a timer countdown at 0. Swift

Does anyone know how I can tell the timer to stop when it reaches 0. Right now it keeps counting down below zero. 

import UIKit

class ViewController: UIViewController {
    var timerCount = 20
    var timerRunning = false
    var timer = NSTimer()

    @IBOutlet weak var timerLabel: UILabel!

    func Counting() {
        timerCount -= 1
        timerLabel.text = "\(timerCount)"
    }

    @IBAction func startButton(sender: UIButton) {
        if timerRunning == false {
            timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector ("Counting"), userInfo: nil, repeats: true)
            timerRunning = true
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        if timerCount == 0 {
            timerRunning = false
        }
    }
}

Upvotes: 0

Views: 3523

Answers (2)

Stefan Arentz
Stefan Arentz

Reputation: 34945

Also, some additional advice: keep local state to a minimum. You can get rid of the timerRunning variable because that state is already in the NSTimer via its valid property.

It simplifies code and results in less state errors if there is only a single place there you look.

Upvotes: 3

ahruss
ahruss

Reputation: 2130

Change your Counting function to this:

func Counting() {
    timerCount -= 1
    timerLabel.text = "\(timerCount)"
    if timerCount == 0 {
        timer.invalidate()
        timerRunning = false
    }
}

From the NSTimer documentation:

Stopping a Timer

invalidate()

Stops the receiver from ever firing again and requests its removal from its run loop.

Discussion

This method is the only way to remove a timer from an NSRunLoop object. The NSRunLoop object removes its strong reference to the timer, either just before the invalidate method returns or at some later point.

If it was configured with target and user info objects, the receiver removes its strong references to those objects as well.

Special Considerations

You must send this message from the thread on which the timer was installed. If you send this message from another thread, the input source associated with the timer may not be removed from its run loop, which could prevent the thread from exiting properly.

Upvotes: 6

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