How to run code asynchronously using GCD async()

Paul Hudson    September 15th 2016    @twostraws

iOS gives you two ways to run code asynchronously: GCD and performSelector(inBackground:). The first option looks like this:

DispatchQueue.global(qos: .userInitiated).async { [unowned self] in
    self.yourCodeHere()
}

The .userInitiated quality of service setting is the highest priority after userInteractive. You can also use utility (lower priority) or .background (lowest priority.)

The second option looks like this:

performSelector(inBackground: #selector(yourCodeHere), with: nil)

You'll need to replace yourCodeHere with the name of an actual method. If you want to pass a parameter, make sure and use “yourCodeHere:" and provide a value for the with parameter.

Available from iOS 4.0 – see Hacking with Swift tutorial 9

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This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.