dispatch_after - GCD in Swift?

Question

I\'ve gone through the iBook from Apple, and couldn\'t find any definition of it:

Can someone explain the structure of dispatch_after?

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Answer 1

use this code to perform some UI related task 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")
            })

Swift 3.0 version

Following closure function execute some task after delay on main thread.

func performAfterDelay(delay : Double, onCompletion: @escaping() -> Void){

    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + delay, execute: {
       onCompletion()
    })
}

Call this function like:

performAfterDelay(delay: 4.0) {
  print("test")
}