How can I use NSTimer in Swift?

Question

I tried

var timer = NSTimer()
timer(timeInterval: 0.01, target: self, selector: update, userInfo: nil, repeats: false)

But, I got an error saying

'(timeInterval: $T1, target: ViewController, selector: () -> (), userInfo: NilType, repeats: Bool) -> $T6' is not identical to 'NSTimer'

Answer 1

Check with:

var timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: Selector("update"), userInfo: nil, repeats: true);

Answer 2

for swift 3 and Xcode 8.2 (nice to have blocks, but if You compile for iOS9 AND want userInfo):

...

        self.timer = Timer(fireAt: fire,
                           interval: deltaT,
                           target: self,
                           selector: #selector(timerCallBack(timer:)),
                           userInfo: ["custom":"data"],
                           repeats: true)

        RunLoop.main.add(self.timer!, forMode: RunLoopMode.commonModes)
        self.timer!.fire()
}

func timerCallBack(timer: Timer!){
        let info = timer.userInfo
        print(info)
    }

Answer 3

Repeated event

You can use a timer to do an action multiple times, as seen in the following example. The timer calls a method to update a label every half second.

Here is the code for that:

import UIKit

class ViewController: UIViewController {

    var counter = 0
    var timer = Timer()

    @IBOutlet weak var label: UILabel!

    // start timer
    @IBAction func startTimerButtonTapped(sender: UIButton) {
        timer.invalidate() // just in case this button is tapped multiple times

        // start the timer
        timer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(timerAction), userInfo: nil, repeats: true)
    }

    // stop timer
    @IBAction func cancelTimerButtonTapped(sender: UIButton) {
        timer.invalidate()
    }

    // called every time interval from the timer
    func timerAction() {
        counter += 1
        label.text = "\(counter)"
    }
}

Delayed event

You can also use a timer to schedule a one time event for some time in the future. The main difference from the above example is that you use repeats: false instead of true.

timer = Timer.scheduledTimer(timeInterval: 2.0, target: self, selector: #selector(delayedAction), userInfo: nil, repeats: false)

The above example calls a method named delayedAction two seconds after the timer is set. It is not repeated, but you can still call timer.invalidate() if you need to cancel the event before it ever happens.

Notes

• If there is any chance of starting your timer instance multiple times, be sure that you invalidate the old timer instance first. Otherwise you lose the reference to the timer and you can't stop it anymore. (see this Q&A)
• Don't use timers when they aren't needed. See the timers section of the Energy Efficiency Guide for iOS Apps.

Related

• How to work with dates and time in Swift

Answer 4

Swift 3, pre iOS 10

func schedule() {
    DispatchQueue.main.async {
      self.timer = Timer.scheduledTimer(timeInterval: 20, target: self,
                                   selector: #selector(self.timerDidFire(timer:)), userInfo: nil, repeats: false)
    }
  }

  @objc private func timerDidFire(timer: Timer) {
    print(timer)
  }

Swift 3, iOS 10+

DispatchQueue.main.async {
      self.timer = Timer.scheduledTimer(withTimeInterval: 20, repeats: false) { timer in
        print(timer)
      }
    }

Notes

• It needs to be on the main queue
• Callback function can be public, private, ...
• Callback function needs to be @objc

Answer 5

timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(createEnemy), userInfo: nil, repeats: true)

And Create Fun By The Name createEnemy

fund createEnemy ()
{
do anything ////
}

Answer 6

As of iOS 10 there is also a new block based Timer factory method which is cleaner than using the selector:

    _ = Timer.scheduledTimer(withTimeInterval: 5, repeats: false) { timer in
        label.isHidden = true
    }