How do you trigger a block after a delay like -performSelector withObject afterDelay

Question

Is there a way to call a block with a primitive parameter after a delay  like using performSelector withObject afterDelay  but with an argument like int double float

User · Answer

Here are my 2 cents   5 methods      I like encapsulate these details and have AppCode tell me how to finish my sentences    void dispatch after delay float delayInSeconds  dispatch queue t queue  dispatch block t block        dispatch time t popTime   dispatch time DISPATCH TIME NOW  delayInSeconds   NSEC PER SEC       dispatch after popTime  queue  block      void dispatch after delay on main queue float delayInSeconds  dispatch block t block        dispatch queue t queue   dispatch get main queue        dispatch after delay delayInSeconds  queue  block      void dispatch async on high priority queue dispatch block t block        dispatch async dispatch get global queue DISPATCH QUEUE PRIORITY HIGH  0   block      void dispatch async on background queue dispatch block t block        dispatch async dispatch get global queue DISPATCH QUEUE PRIORITY BACKGROUND  0   block      void dispatch async on main queue dispatch block t block        dispatch async dispatch get main queue    block

User · Answer

You can either wrap the argument in your own class  or wrap the method call in a method that doesn t need to be passed in the primitive type  Then call that method after your delay  and within that method perform the selector you wish to perform

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For Swift I ve created a global function  nothing special  using the dispatch after method  I like this more as it s readable and easy to use   func performBlock block    - gt  Void  afterDelay delay NSTimeInterval       dispatch after dispatch time DISPATCH TIME NOW  Int64 delay   Double NSEC PER SEC     dispatch get main queue    block      Which you can use as followed   performBlock      - gt  Void in        Perform actions    afterDelay  0 3

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You can use dispatch after to call a block later  In Xcode  start typing dispatch after and hit Enter to autocomplete to the following     Here s an example with two floats as  arguments   You don t have to rely on any type of macro  and the intent of the code is quite clear    Swift 3  Swift 4  let time1   8 23 let time2   3 42     Delay 2 seconds DispatchQueue main asyncAfter deadline   now     2 0        print  Sum of times    time1   time2        Swift 2  let time1   8 23 let time2   3 42     Delay 2 seconds dispatch after dispatch time DISPATCH TIME NOW  Int64 2 0   Double NSEC PER SEC     dispatch get main queue         - gt  Void in         println  Sum of times    time1   time2        Objective C  CGFloat time1   3 49  CGFloat time2   8 13      Delay 2 seconds dispatch after dispatch time DISPATCH TIME NOW   int64 t  2 0   NSEC PER SEC    dispatch get main queue           CGFloat newTime   time1   time2      NSLog   New time   f   newTime

User · Answer

verified on Xcode 11 3 1 in June 2020   Xcode provides a code snippet to do this  You just have to enter the delay value and the code you wish to run after the delay    click on the   button at the top right of Xcode  search for after It will return only 1 search result  which is the desired snippet  see screenshot   Double click it and you re good to go

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There s a nice one in the BlocksKit framework   BlocksKit   and the class   BBlocksKit m

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Here s the Swift 3 way to queue work after a delay   DispatchQueue main asyncAfter    DispatchTime now     DispatchTimeInterval seconds 2            do work

User · Answer

Swift 3  amp  Xcode 8 3 2  This code will help you  i add an explanation too     Create custom class  this will make your life easier class CustomDelay        static let cd   CustomDelay           This is your custom delay function     func runAfterDelay   delay Double  closure  escaping   - gt               let when   DispatchTime now     delay         DispatchQueue main asyncAfter deadline  when  execute  closure               here how to use it  Example 1  class YourViewController  UIViewController           example delay time 2 second     let delayTime   2 0      override func viewDidLoad             super viewDidLoad            CustomDelay cd runAfterDelay delayTime                   This func will run after 2 second                Update your UI here  u don t need to worry to bring this to the main thread because your CustomDelay already make this to main thread automatically                self runFunc                           example function 1     func runFunc                do your method 1 here             here how to use it  Example 2  class YourSecondViewController  UIViewController           let say you want to user run function shoot after 3 second they tap a button         Create a button  This is programatically  you can create with storyboard too      let shootButton  UIButton             let button   UIButton type   system          button frame   CGRect x  15  y  15  width  40  height  40     Customize where do you want to put your button inside your ui         button setTitle  Shoot   for   normal          button translatesAutoresizingMaskIntoConstraints   false         return button              override func viewDidLoad             super viewDidLoad               create an action selector when user tap shoot button         shootButton addTarget self  action   selector shoot   for   touchUpInside                   example shoot function     func shoot                example delay time 3 second then shoot         let delayTime   3 0             delay a shoot after 3 second         CustomDelay cd runAfterDelay delayTime                   your shoot method here                Update your UI here  u don t need to worry to bring this to the main thread because your CustomDelay already make this to main thread automatically

User · Answer

Here is how you can trigger a block after a delay in Swift   runThisAfterDelay seconds  2       - gt     in     print  Prints this 2 seconds later in main queue          EZSwiftExtensions func runThisAfterDelay seconds seconds  Double  after     - gt            let time   dispatch time DISPATCH TIME NOW  Int64 seconds   Double NSEC PER SEC        dispatch after time  dispatch get main queue    after      Its included as a standard function in my repo

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How about using Xcode built-in code snippet library   Update for Swift  Many up votes inspired me to update this answer  The build-in Xcode code snippet library has dispatch after for only objective-c language  People can also create their own Custom Code Snippet for Swift  Write this in Xcode  dispatch after dispatch time DISPATCH TIME NOW  Int64  lt  delayInSeconds  gt    Double NSEC PER SEC     dispatch get main queue               lt  code to be executed after a specified delay  gt          Drag this code and drop it in the code snippet library area   Bottom of the code snippet list  there will be a new entity named My Code Snippet  Edit this for a title  For suggestion as you type in the Xcode fill in the Completion Shortcut  For more info see CreatingaCustomCodeSnippet  Update Swift 3 Drag this code and drop it in the code snippet library area  DispatchQueue main asyncAfter deadline   now      seconds  lt  delayInSeconds  gt           lt  code to be executed after a specified delay  gt

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Here s a handy helper to prevent making the annoying GCD call over and over again   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 the Main thread like this   delay bySeconds  1 5            delayed code     If you want to delay your code to different thread   delay bySeconds  1 5  dispatchLevel   background            delayed code that will run on background thread       If you prefer a Framework that also has some more handy features then checkout HandySwift  You can add it to your project via Carthage then use it exactly like in the examples above   import HandySwift      delay bySeconds  1 5            delayed code

User · Answer

I think you re looking for dispatch after     It requires your block to accept no parameters  but you can just let the block capture those variables from your local scope instead   int parameter1   12  float parameter2   144 1      Delay execution of my block for 10 seconds  dispatch after dispatch time DISPATCH TIME NOW  10   NSEC PER SEC   dispatch get main queue           NSLog   parameter1   d parameter2   f   parameter1  parameter2         More  https   developer apple com documentation dispatch 1452876-dispatch after

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I believe the author is not asking how to wait for a fractional time  delay   but instead how to pass a scalar as argument of the selector  withObject   and the fastest way in modern objective C is    obj performSelector      withObject   0 123123123  afterDelay 10    your selector have to change its parameter to NSNumber  and retrieve the value using a selector like floatValue or doubleValue

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PerformSelector WithObject always takes an object  so in order to pass arguments like int double float etc      You can use something like this     NSNumber is an object     self performSelector  selector setUserAlphaNumber        withObject   NSNumber numberWithFloat  1 0f              afterDelay 1 5      - void  setUserAlphaNumber   NSNumber   number         txtUsername setAlpha   number floatValue          Same way you can use  NSNumber numberWithInt   etc     and in the receiving method you can convert the number into your format as  number int  or  number double

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Perhaps simpler than going thru GCD  in a class somewhere  e g   Util    or a Category on Object      void runBlock  void       block       block         void runAfterDelay  CGFloat delay block  void       block        void   block         block copy  autorelease        self performSelector  selector runBlock   withObject block  afterDelay delay       So to use    Util runAfterDelay 2 block        NSLog   two seconds later

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Xcode 10 2 and Swift 5 and above  DispatchQueue main asyncAfter deadline   now     2  execute          code to execute

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Expanding on Jaime Cham s answer I created a NSObject Blocks category as below   I felt these methods better matched the existing performSelector  NSObject methods   NSObject Blocks h   import  lt Foundation Foundation h gt    interface NSObject  Blocks   -  void performBlock  void       block afterDelay  NSTimeInterval delay    end   NSObject Blocks m   import  NSObject Blocks h    implementation NSObject  Blocks   -  void performBlock  void       block       block       -  void performBlock  void       block afterDelay  NSTimeInterval delay       void   block        block copy      autorelease this if you re not using ARC      self performSelector  selector performBlock   withObject block  afterDelay delay       end   and use like so    anyObject performBlock         anotherObject doYourThings stuff     afterDelay 0 15

User · Answer

In swift 3  We can simply use  DispatchQueue main asyncAfter function to trigger any function or action after the delay of  n  seconds  Here in code we have set delay after 1 second  You call any function inside the body of this function which will trigger after the delay of 1 second   let when   DispatchTime now     1 DispatchQueue main asyncAfter deadline  when            Trigger the function action after the delay of 1Sec

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The dispatch after function dispatches a block object to a dispatch queue after a given period of time  Use below code to perform some UI related taks after 2 0 seconds               let delay   2 0             let delayInNanoSeconds   dispatch time DISPATCH TIME NOW  Int64 delay   Double NSEC PER SEC                let mainQueue   dispatch get main queue                dispatch after delayInNanoSeconds  mainQueue                     print  Some UI related task after delay                    In swift 3 0                let dispatchTime  DispatchTime   DispatchTime now     Double Int64 2 0   Double NSEC PER SEC      Double NSEC PER SEC              DispatchQueue main asyncAfter deadline  dispatchTime  execute

[ios] How do you trigger a block after a delay, like -performSelector:withObject:afterDelay:?

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