How to create a delay in Swift

Question

I want to pause my app at a certain in point  In other words  I want my app to execute the code  but then at a certain point  pause for 4 seconds  and then continue on with the rest of the code  How can I do this   I am using Swift

User · Answer

Try the following implementation in Swift 3.0

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

Usage

delayWithSeconds(1) {
   //Do something
}

User · Answer

Instead of a sleep  which will lock up your program if called from the UI thread  consider using NSTimer or a dispatch timer   But  if you really need a delay in the current thread   do       sleep 4      This uses the sleep function from UNIX

User · Answer

Using a dispatch after block is in most cases better than using sleep time  as the thread on which the sleep is performed is blocked from doing other work  when using dispatch after the thread which is worked on does not get blocked so it can do other work in the meantime   If you are working on the main thread of your application  using sleep time  is bad for the user experience of your app as the UI is unresponsive during that time  Dispatch after schedules the execution of a block of code instead of freezing the thread   Swift   3 0  let seconds   4 0 DispatchQueue main asyncAfter deadline   now     seconds           Put your code which should be executed with a delay here     Swift  lt  3 0  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

User · Answer

this is the simplest      delay 0 3  closure               put her any code you want to fire it with delay         button removeFromSuperview

User · Answer

If you need to set a delay of less than a second  it is not necessary to set the  seconds parameter  I hope this is useful to someone   DispatchQueue main asyncAfter deadline   now     0 5  execute               your code hear

User · Answer

DispatchQueue global qos   background  async       sleep 4      print  Active after 4 sec  and doesn t block main       DispatchQueue main async            do stuff in the main thread here

User · Answer

I agree with Palle that using dispatch after is a good choice here  But you probably don t like the GCD calls as they are quite annoying to write  Instead you can add this handy helper  public func delay bySeconds seconds  Double  dispatchLevel  DispatchLevel    main  closure   escaping    - gt  Void        let dispatchTime   DispatchTime now     seconds     dispatchLevel dispatchQueue asyncAfter deadline  dispatchTime  execute  closure     public enum DispatchLevel       case main  userInteractive  userInitiated  utility  background     var dispatchQueue  DispatchQueue           switch self           case  main                  return DispatchQueue main         case  userInteractive       return DispatchQueue global qos   userInteractive          case  userInitiated         return DispatchQueue global qos   userInitiated          case  utility               return DispatchQueue global qos   utility          case  background            return DispatchQueue global qos   background                     Now you simply delay your code on a background thread like this  delay bySeconds  1 5  dispatchLevel   background            delayed code that will run on background thread    Delaying code on the main thread is even simpler  delay bySeconds  1 5            delayed code  by default run in main thread     If you prefer a Framework that also has some more handy features then checkout HandySwift  You can add it to your project via SwiftPM then use it exactly like in the examples above  import HandySwift      delay by   seconds 1 5             delayed code

User · Answer

In Swift 4 2 and Xcode 10 1  You have 4 ways total to delay  Out of these option 1 is preferable to call or execute a function after some time  The sleep   is least case in use   Option 1   DispatchQueue main asyncAfter deadline   now     5 0        self yourFuncHere       Your function here     func yourFuncHere          Option 2   perform  selector yourFuncHere2   with  nil  afterDelay  5 0     Your function here    objc func yourFuncHere2         print  this is          Option 3   Timer scheduledTimer timeInterval  5 0  target  self  selector   selector yourFuncHere3   userInfo  nil  repeats  false     Your function here    objc func yourFuncHere3          Option 4   sleep 5    If you want to call a function after some time to execute something don t use sleep

User · Answer

You can create extension to use delay function easily  Syntax  Swift 4 2    extension UIViewController       func delay   delay Double  closure  escaping   - gt               DispatchQueue main asyncAfter              deadline  DispatchTime now     Double Int64 delay   Double NSEC PER SEC      Double NSEC PER SEC   execute  closure            How to use in UIViewController  self delay 0 1  closure         execute code

User · Answer

To create a simple time delay  you can import Darwin and then use sleep seconds  to do the delay  That only takes whole seconds  though  so for more precise measurements you can import Darwin and use usleep millionths of a second  for very precise measurement  To test this  I wrote   import Darwin print  This is one    sleep 1  print  This is two    usleep 400000  print  This is three      Which prints  then waits for 1 sec and prints  then waits for 0 4 sec then prints  All worked as expected

User · Answer

Comparison between different approaches in swift 3 0  1  Sleep  This method does not have a call back  Put codes directly after this line to be executed in 4 seconds  It will stop user from iterating with UI elements like the test button until the time is gone  Although the button is kind of frozen when sleep kicks in  other elements like activity indicator is still spinning without freezing  You cannot trigger this action again during the sleep   sleep 4  print  done    Do stuff here     2  Dispatch  Perform and Timer  These three methods work similarly  they are all running on the background thread with call backs  just with different syntax and slightly different features   Dispatch is commonly used to run something on the background thread  It has the callback as part of the function call  DispatchQueue main asyncAfter deadline   now      seconds 4   execute        print  done        Perform is actually a simplified timer  It sets up a timer with the delay  and then trigger the function by selector   perform  selector callback   with  nil  afterDelay  4 0   func callback         print  done        And finally  timer also provides ability to repeat the callback  which is not useful in this case  Timer scheduledTimer timeInterval  4  target  self  selector   selector callback   userInfo  nil  repeats  false    func callback         print  done        For all these three method  when you click on the button to trigger them  UI will not freeze and you are allowed to click on it again  If you click on the button again  another timer is set up and the callback will be triggered twice     In conclusion  None of the four method works good enough just by themselves  sleep will disable user interaction  so the screen  freezes  not actually  and results bad user experience  The other three methods will not freeze the screen  but you can trigger them multiple times  and most of the times  you want to wait until you get the call back before allowing user to make the call again    So a better design will be using one of the three async methods with screen blocking  When user click on the button  cover the entire screen with some translucent view with a spinning activity indicator on top  telling user that the button click is being handled  Then remove the view and indicator in the call back function  telling user that the the action is properly handled  etc

User · Answer

You can also do this with Swift 3    Perform the function after delay like so   override func viewDidLoad         super viewDidLoad        self perform  selector ClassName performAction   with  nil  afterDelay  2 0            objc func performAction       This function will perform after 2 seconds             print  Delayed

User · Answer

If your code is already running in a background thread  pause the thread using this method in Foundation  Thread sleep forTimeInterval    For example   DispatchQueue global qos   userInitiated  async           Code is running in a background thread already so it is safe to sleep     Thread sleep forTimeInterval  4 0       See other answers for suggestions when your code is running on the main thread

User · Answer

NSTimer The answer by  nneonneo suggested using NSTimer but didn t show how to do it  This is the basic syntax  let delay   0 5    time in seconds NSTimer scheduledTimerWithTimeInterval delay  target  self  selector   selector myFunctionName   userInfo  nil  repeats  false   Here is a very simple project to show how it might be used  When a button is pressed it starts a timer that will call a function after a delay of half a second  import UIKit class ViewController  UIViewController        var timer   NSTimer       let delay   0 5             start timer when button is tapped      IBAction func startTimerButtonTapped sender  UIButton                cancel the timer in case the button is tapped multiple times         timer invalidate               start the timer         timer   NSTimer scheduledTimerWithTimeInterval delay  target  self  selector   selector delayedAction   userInfo  nil  repeats  false                function to be called after the delay     func delayedAction             print  quot action has started quot            Using dispatch time  as in Palle s answer  is another valid option  However  it is hard to cancel  With NSTimer  to cancel a delayed event before it happens  all you need to do is call timer invalidate    Using sleep is not recommended  especially on the main thread  since it stops all the work being done on the thread  See here for my fuller answer

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