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How to run code after a delay using asyncAfter() and perform()

Swift version: 5.0

Paul Hudson    @twostraws   

There are two ways to run code after a delay using Swift: GCD and perform(_:with:afterDelay:), but GCD has the advantage that it can run arbitrary blocks of code, whereas the perform() method runs methods.

So, using GCD we can write something that runs code after a half-second delay:

DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
    // your code here
}

An alternative option is to use perform(_:with:afterDelay:), which lets you specify a method to call after a certain time has elapsed.

To call the authenticate() method after 1 second, you would use this code:

perform(#selector(authenticate), with: nil, afterDelay: 1)

Note: any method called using perform(_:with:afterDelay:) must be marked with the @objc attribute.

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Available from iOS 4.0

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