Do something every x minutes in Swift

Question

How can I run a function every minute? In JavaScript I can do something like setInterval, does something similar exist in Swift?

Wanted output:

Hello World once a minute...

Answer 1

var helloWorldTimer = NSTimer.scheduledTimerWithTimeInterval(60.0, target: self, selector: Selector("sayHello"), userInfo: nil, repeats: true)

func sayHello() 
{
    NSLog("hello World")
}

Remember to import Foundation.

Swift 4:

 var helloWorldTimer = Timer.scheduledTimer(timeInterval: 60.0, target: self, selector: #selector(ViewController.sayHello), userInfo: nil, repeats: true)

 @objc func sayHello() 
 {
     NSLog("hello World")
 }

Answer 2

If targeting iOS version 10 and greater, you can use the block-based rendition of Timer, which simplifies the potential strong reference cycles, e.g.:

weak var timer: Timer?

func startTimer() {
    timer?.invalidate()   // just in case you had existing `Timer`, `invalidate` it before we lose our reference to it
    timer = Timer.scheduledTimer(withTimeInterval: 60.0, repeats: true) { [weak self] _ in
        // do something here
    }
}

func stopTimer() {
    timer?.invalidate()
}

// if appropriate, make sure to stop your timer in `deinit`

deinit {
    stopTimer()
}

---

While Timer is generally best, for the sake of completeness, I should note that you can also use dispatch timer, which is useful for scheduling timers on background threads. With dispatch timers, since they're block-based, it avoids some of the strong reference cycle challenges with the old target/selector pattern of Timer, as long as you use weak references.

So:

var timer: DispatchSourceTimer?

func startTimer() {
    let queue = DispatchQueue(label: "com.domain.app.timer")  // you can also use `DispatchQueue.main`, if you want
    timer = DispatchSource.makeTimerSource(queue: queue)
    timer!.schedule(deadline: .now(), repeating: .seconds(60))
    timer!.setEventHandler { [weak self] in
        // do whatever you want here
    }
    timer!.resume()
}

func stopTimer() {
    timer = nil
}

For more information, see the the Creating a Timer section of Dispatch Source Examples in the Dispatch Sources section of the Concurrency Programming Guide.

---

For Swift 2, see previous revision of this answer.

Answer 3

If you can allow for some time drift here's a simple solution executing some code every minute:

private func executeRepeatedly() {
    // put your code here

    DispatchQueue.main.asyncAfter(deadline: .now() + 60.0) { [weak self] in
        self?.executeRepeatedly()
    }
}

Just run executeRepeatedly() once and it'll be executed every minute. The execution stops when the owning object (self) is released. You also can use a flag to indicate that the execution must stop.

Answer 4

Here's an update to the NSTimer answer, for Swift 3 (in which NSTimer was renamed to Timer) using a closure rather than a named function:

var timer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true) {
    (_) in
    print("Hello world")
}

Answer 5

You can use Timer (swift 3)

var timer = Timer.scheduledTimerWithTimeInterval(60, target: self, selector: Selector("function"), userInfo: nil, repeats: true)

In selector() you put in your function name

Answer 6

In swift 3.0 the GCD got refactored:

let timer : DispatchSourceTimer = DispatchSource.makeTimerSource(flags: [], queue: DispatchQueue.main)

timer.scheduleRepeating(deadline: .now(), interval: .seconds(60))
timer.setEventHandler
{
    NSLog("Hello World")
}
timer.resume()

This is specially useful for when you need to dispatch on a particular Queue. Also, if you're planning on using this for user interface updating, I suggest looking into CADisplayLink as it's synchronized with the GPU refresh rate.

Answer 7

Here is another version algrid's answer with an easy way to stop it

@objc func executeRepeatedly() {

    print("--Do something on repeat--")
        
    perform(#selector(executeRepeatedly), with: nil, afterDelay: 60.0)
}

Here's an example of how to start it and stop it:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    executeRepeatedly() // start it
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)

    NSObject.cancelPreviousPerformRequests(withTarget: self) // stop it
}

Answer 8

timer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true, block: myMethod)

func myMethod(_:Timer) {
...
}

or

timer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true) { _ in
...
}

make sure to invalid the timer at some point like your time is no longer visible, or you object is deist