How do I write dispatch after GCD in Swift 3 4 and 5

Question

In Swift 2  I was able to use dispatch after to delay an action using grand central dispatch   var dispatchTime  dispatch time t   dispatch time DISPATCH TIME NOW  Int64 0 1   Double NSEC PER SEC     dispatch after dispatchTime  dispatch get main queue              your function here       But this no longer seems to compile since Swift 3  What is the preferred way to write this in modern Swift

User · Answer

If you just want the delay function in  Swift 4  amp  5  func delay interval  TimeInterval  closure   escaping    - gt  Void         DispatchQueue main asyncAfter deadline   now     interval              closure              You can use it like   delay interval  1         print  Hi

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None of the answers mentioned running on a non-main thread  so adding my 2 cents       On main queue  main thread      let mainQueue   DispatchQueue main let deadline   DispatchTime now      seconds 10  mainQueue asyncAfter deadline  deadline                   OR  DispatchQueue main asyncAfter deadline  DispatchTime now      seconds 10                     On global queue  non main thread  based on QOS specified        let backgroundQueue   DispatchQueue global   let deadline   DispatchTime now      milliseconds 100  backgroundQueue asyncAfter deadline  deadline  qos   background                    OR  DispatchQueue global   asyncAfter deadline  DispatchTime now      milliseconds 100   qos   background

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Swift 5 and above  DispatchQueue main asyncAfter deadline   now     2  execute          code to execute

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You can use  DispatchQueue main asyncAfter deadline   now      microseconds 100                Code

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The syntax is simply      to run something in 0 1 seconds  DispatchQueue main asyncAfter deadline   now     0 1           your code here       Note  the above syntax of adding seconds as a Double seems to be a source of confusion  esp since we were accustomed to adding nsec   That  add seconds as Double  syntax works because deadline is a DispatchTime and  behind the scenes  there is a   operator that will take a Double and add that many seconds to the DispatchTime   public func   time  DispatchTime  seconds  Double  - gt  DispatchTime   But  if you really want to add an integer number of msec    s  or nsec to the DispatchTime  you can also add a DispatchTimeInterval to a DispatchTime  That means you can do   DispatchQueue main asyncAfter deadline   now      milliseconds 500         os log  500 msec seconds later      DispatchQueue main asyncAfter deadline   now      microseconds 1 000 000         os log  1m   s seconds later      DispatchQueue main asyncAfter deadline   now      nanoseconds 1 500 000 000         os log  1 5b nsec seconds later       These all seamlessly work because of this separate overload method for the   operator in the DispatchTime class   public func   time  DispatchTime  interval  DispatchTimeInterval  - gt  DispatchTime     It was asked how one goes about canceling a dispatched task  To do this  use DispatchWorkItem  For example  this starts a task that will fire in five seconds  or if the view controller is dismissed and deallocated  its deinit will cancel the task   class ViewController  UIViewController        private var item  DispatchWorkItem       override func viewDidLoad             super viewDidLoad            item   DispatchWorkItem    weak self  in             self  doSomething               self  item   nil                    DispatchQueue main asyncAfter deadline   now     5  execute  item              deinit           item  cancel              func doSomething                Note the use of the  weak self  capture list in the DispatchWorkItem  This is essential to avoid a strong reference cycle  Also note that this does not do a preemptive cancelation  but rather just stops the task from starting if it hasn   t already  But if it has already started by the time it encounters the cancel   call  the block will finish its execution  unless you   re manually checking isCancelled inside the block

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Swift 4  You can create a extension on DispatchQueue and add function delay which uses DispatchQueue asyncAfter function internally  extension DispatchQueue      static func delay   delay  DispatchTimeInterval  closure   escaping    - gt              DispatchQueue main asyncAfter deadline   now     delay  execute  closure           and use   DispatchQueue delay  milliseconds 10        print  task to be done

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after Swift 3 release  also the  escaping has to be added  func delay   delay  Double  closure   escaping    - gt          DispatchQueue main asyncAfter deadline   now     delay        closure

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Swift 4   DispatchQueue main asyncAfter deadline   now      milliseconds 100           Code     For the time  seconds Int    microseconds Int  and  nanoseconds Int  may also be used

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In Swift 4 1 and Xcode 9 4 1  Simple answer is       To call function after 5 seconds time DispatchQueue main asyncAfter deadline   now     5 0      Here call your function

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This worked for me in Swift 3  let time1   8 23 let time2   3 42     Delay 2 seconds   DispatchQueue main asyncAfter deadline   now     2 0        print  Sum of times    time1   time2

User · Answer

try this  let when   DispatchTime now     1 5     DispatchQueue main asyncAfter deadline  when              some code

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call DispatchQueue main after when  DispatchTime  execute     - gt  Void   I d highly recommend using the Xcode tools to convert to Swift 3  Edit   Convert   To Current Swift Syntax   It caught this for me

User · Answer

A somewhat different flavour of the Accepted Answer   Swift 4  DispatchQueue main asyncAfter deadline   now     0 1    milliseconds 500      microseconds 500     nanoseconds 1000                     print  Delayed by 0 1 second   500 milliseconds   500 microseconds                          1000 nanoseconds

[swift] How do I write dispatch_after GCD in Swift 3, 4, and 5?

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