How to program a delay in Swift 3

Question

In earlier versions of Swift, one could create a delay with the following code:

let time = dispatch_time(dispatch_time_t(DISPATCH_TIME_NOW), 4 * Int64(NSEC_PER_SEC)) dispatch_after(time, dispatch_get_main_queue()) { //put your code which should be executed with a delay here }

But now, in Swift 3, Xcode automatically changes 6 different things but then the following error appears: "Cannot convert DispatchTime.now to expected value dispatch_time_t aka UInt64."

How can one create a delay before running a sequence of code in Swift 3?

Daniel Storm · Accepted Answer · 2019-01-09 17:48:58Z

1177

After a lot of research, I finally figured this one out.

DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) { // Change `2.0` to the desired number of seconds. // Code you want to be delayed }

This creates the desired "wait" effect in Swift 3 and Swift 4.

Inspired by a part of this answer.

edited Jan 9, 2019 at 17:48

Daniel Storm

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answered Jun 25, 2016 at 17:30

owlswipe

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9 Comments

RenniePet Over a year ago

You could make your code a bit more swifty by replacing "+ 2" with "+ .seconds(2)". Or, for the ultimate in swiftyness, you could drop the first line and replace "deadline: when" with "deadline: .now() + .seconds(2)".

owlswipe Over a year ago

@OctavioAntonioCedeño Happy to help. This really bugged me for a while :D

jiawen Over a year ago

if the delay is long, say 10 min, and the phone goes to sleep. the task will never be run even after the phone is woken up after 10 min.

owlswipe Over a year ago

@jiawen That's true, but that would be the case with any such delay. I can't think of a use case other than notifications where this could be an issue, and for waiting to send a notification you should definitely use .firedate instead.

owlswipe Over a year ago

Working on iOS 11 and Swift 4!

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byaruhaf · Accepted Answer · 2019-12-21 12:58:48Z

I like one-line notation for GCD, it's more elegant:

 DispatchQueue.main.asyncAfter(deadline: .now() + 42.0) { // do stuff 42 seconds later }

Also, in iOS 10 we have new Timer methods, e.g. block initializer:

(so delayed action may be canceled)

 let timer = Timer.scheduledTimer(withTimeInterval: 42.0, repeats: false) { (timer) in // do stuff 42 seconds later }

Btw, keep in mind: by default, timer is added to the default run loop mode. It means timer may be frozen when the user is interacting with the UI of your app (for example, when scrolling a UIScrollView) You can solve this issue by adding the timer to the specific run loop mode:

RunLoop.current.add(timer, forMode: .common)

At this blog post you can find more details.

plus one for the Timer comparison and the disclaimer about the main runloop!

Vakas · Accepted Answer · 2017-12-17 08:52:34Z

Try the following function implemented in Swift 3.0 and above

func delayWithSeconds(_ seconds: Double, completion: @escaping () -> ()) { DispatchQueue.main.asyncAfter(deadline: .now() + seconds) { completion() } }

Usage

delayWithSeconds(1) { //Do something }

You basically just copied this answer but yes this is good, thanks.

Peter · Accepted Answer · 2018-12-29 12:28:27Z

14

Try the below code for delay

//MARK: First Way func delayForWork() { delay(3.0) { print("delay for 3.0 second") } } delayForWork()

// MARK: Second Way DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) { // your code here delayed by 0.5 seconds }

edited Dec 29, 2018 at 12:28

Peter

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answered May 31, 2018 at 12:18

Anand Verma

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2 Comments

Jerry Chong Over a year ago

First way displays have error "Use of unresolved identifier 'delay'"

Nick Perkins Over a year ago

This programmer is working with a helper method in his code base and has for a long time. So delay was code he has used for a while not knowing it is not apart of Apple's SDK.

Paul B · Accepted Answer · 2021-10-31 17:21:19Z

Most common things to use are asyncAfter() and Timer. But if blocking thread is OK, then there is an option:

sleep(3) // in seconds usleep // in 1/million of second

For asynchronous programming (Swift 5.5) pausing in func looks like this:

func someAsyncFunc() async { await Task.sleep(2_000_000_000) // Two seconds // Code to be executed with a delay here }

sleep(3) worked for me. Got a compilation error on usleep.
usleep needs and argument, of course, @AbdurrahmanMubeenAli. Something like usleep(3000000).

Zohaib Brohi · Accepted Answer · 2019-07-25 11:09:58Z

One way is to use DispatchQueue.main.asyncAfter as a lot of people have answered.

Another way is to use perform(_:with:afterDelay:). More details here

perform(#selector(delayedFunc), with: nil, afterDelay: 3) @IBAction func delayedFunc() { // implement code }

Pratyush Pratik Sinha · Accepted Answer · 2018-02-28 13:09:50Z

//Runs function after x seconds

public static func runThisAfterDelay(seconds: Double, after: @escaping () -> Void) { runThisAfterDelay(seconds: seconds, queue: DispatchQueue.main, after: after) } public static func runThisAfterDelay(seconds: Double, queue: DispatchQueue, after: @escaping () -> Void) { let time = DispatchTime.now() + Double(Int64(seconds * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC) queue.asyncAfter(deadline: time, execute: after) }

//Use:-

runThisAfterDelay(seconds: x){ //write your code here }

leo · Accepted Answer · 2023-08-17 17:18:32Z

UI can also use Task as shown in MultiNodeTestConductor.swift:

/// puse execution by the given druation private func delayUiUpdate(duration: Double) async { do { try await Task.sleep(until: .now + .seconds(duration), clock: .continuous) } catch { logger.error("Task delay error \(error.localizedDescription)") } }

You call it like this:

await delayUiUpdate(duration: 2)

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