NEW: Master Swift design patterns with my latest book! >>

How to run code asynchronously using GCD async()

Written by Paul Hudson    @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

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

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

Need to know Objective-C fast?

I wrote a book dedicated to teaching Objective-C to developers who already know Swift – it's the fastest way to get up to speed!

Click here to visit the Hacking with Swift store >>