Delaying function in swift

Question

I don't have a code to sample or anything, because I have no idea how to do it, but can someone please tell me how to delay a function with swift for a set amount of time?

You should include things you've tried/looked up. I know the language is fairly new, but it has to have documentation somewhere. — Carcigenicate, Mar 03 '15 at 00:05
Not the most legitimate of sources, but give this a look over: http://www.reddit.com/r/swift/comments/28v5pv/wait_function/ — Carcigenicate, Mar 03 '15 at 00:07
Just a word of advice – there are countless examples of how to do this in Obj-C. If you ever want to be a competent iOS developer, you will need to learn Obj-C, or at least how to translate Obj-C into Swift. — AdamPro13, Mar 03 '15 at 00:12
To name a couple of methods, take a look in the Apple documentation at dispatch_after and NSTimer. — MirekE, Mar 03 '15 at 00:14
^ No, don't use `sleep(10)`. That will put the entire thread to sleep. — AdamPro13, Mar 03 '15 at 00:23
The best one around [Matt's Answer](http://stackoverflow.com/a/24318861/3648310) — Supratik Majumdar, Sep 01 '16 at 07:31

score 458 · Accepted Answer · edited Oct 22 '21 at 09:34

458

You can use GCD (in the example with a 10 second delay):

Swift 2

let triggerTime = (Int64(NSEC_PER_SEC) * 10)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, triggerTime), dispatch_get_main_queue(), { () -> Void in
    self.functionToCall()
})

Swift 3 and Swift 4

DispatchQueue.main.asyncAfter(deadline: .now() + 10.0, execute: {
    self.functionToCall()
})

Swift 5 or Later

 DispatchQueue.main.asyncAfter(deadline: .now() + 10.0) {
        //call any function
 }

edited Oct 22 '21 at 09:34

Mudith Chathuranga Silva

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answered Mar 03 '15 at 00:13

Farlei Heinen

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GCD stands for "Grand Central Dispatch". Apple define it as: _Grand Central Dispatch (GCD) comprises language features, runtime libraries, and system enhancements that provide systemic, comprehensive improvements to the support for concurrent code execution on multicore hardware in iOS and OS X._ You can find more info [HERE](https://developer.apple.com/library/ios/documentation/Performance/Reference/GCD_libdispatch_Ref/) – Farlei Heinen Jun 01 '16 at 04:18
1

What if you wanted to do a fraction of a second say 0.5? – Cody Weaver Aug 17 '16 at 13:38
1

@CodyWeaver: then you need to change the first line cast to: `let triggerTime = (Int64(Double(NSEC_PER_SEC) * 0.5))` – Farlei Heinen Aug 17 '16 at 21:00
What's the reason I should use this method and not something like NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(3), target: self, selector: "functionHere", userInfo: nil, repeats: false) ? – Lucas van Dongen Nov 15 '16 at 22:10
I think the main reason is code locality. All the logic is on the same block. But if you want a repeating block NSTimer is better. – Farlei Heinen Nov 15 '16 at 22:21
Where do you get DISPATCH_TIME_NOW – Droid Chris Feb 05 '17 at 00:22
1

@DroidChris - If you are trying this code in Swift 3 you need to use DispatchTime.now() - The code in this answer is for Swift 2 – Farlei Heinen Feb 06 '17 at 20:55
how to call the function on class method , where we can use Self.functioncall() ? – Tejas Jun 23 '17 at 14:24
This, like 99% of answers to the simple question: "how to delay code?" misses the point. The question does not ask how to call another function after a delay, but to simply add a delay a function. Semantics here are everything. – drew.. Jun 10 '18 at 12:31
deadline: .now() + .seconds(10) – nbaroz Jun 28 '20 at 12:27

Anand · Answer 2 · 2019-10-15T05:55:54.013

38

Swift 3 and Above Version(s) for a delay of 10 seconds

    DispatchQueue.main.asyncAfter(deadline: .now() + 10) { [unowned self] in
        self.functionToCall()
    }

edited Oct 15 '19 at 05:55

answered Oct 15 '16 at 11:58

Anand

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DispatchQueue.main.asyncAfter(deadline: .now() + 10, execute: { something() }) – Nov 02 '16 at 14:00
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WRT the unowned self, I think it is better to declare unowned self in the lambda, e.g., `{ [unowned self] in self.functionToCall() }`. That way the class doesn't have an unowned reference that it really doesn't need. – sschilli Oct 14 '19 at 16:54
@sschilli: Thanks for the comment. Updated the code. – Anand Oct 15 '19 at 05:57

score 24 · Answer 3 · answered Apr 19 '15 at 12:10

24

 NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(3), target: self, selector: "functionHere", userInfo: nil, repeats: false)

This would call the function functionHere() with a 3 seconds delay

answered Apr 19 '15 at 12:10

JChomali

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how to send argument in that function functionHere()? – PAC Feb 11 '16 at 18:03
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Swift 3 version of this: Timer.scheduledTimer(timeInterval: TimeInterval(3), target: self, selector: "functionHere", userInfo: nil, repeats: false) – Anooj Krishnan G Nov 08 '16 at 11:59

score 4 · Answer 4 · answered Feb 23 '16 at 00:32

For adding argument to delay function.

First setup a dictionary then add it as the userInfo. Unwrap the info with the timer as the argument.

let arg : Int = 42
let infoDict : [String : AnyObject] = ["argumentInt", arg]

NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(3), target: self, selector: "functionHereWithArgument:", userInfo: infoDict, repeats: false)

Then in the called function

func functionHereWithArgument (timer : NSTimer)
{
    if let userInfo = timer.userInfo as? Dictionary<String, AnyObject>
    {
         let argumentInt : Int = (userInfo[argumentInt] as! Int)
    }
}

Delaying function in swift

4 Answers4

Swift 2

Swift 3 and Swift 4

Swift 5 or Later

Linked