UPGRADE YOUR SKILLS: Learn advanced Swift and SwiftUI on Hacking with Swift+! >>

What are property observers?

Swift version: 5.6

Paul Hudson    @twostraws   

Property observers are Swift's way of letting you attach functionality to changes in property values. For example, you might want to say, "whenever the player's score changes, update this label to show their new score." Here's a basic example that prints message to the debug console when a variable changes:

var score = 0 {
    willSet {
        print("Score is about to change to \(newValue)")
    }

    didSet {
        print("Score just changed from \(oldValue) to \(score)")
    }
}

score = 10
Hacking with Swift is sponsored by RevenueCat

SPONSORED Take the pain out of configuring and testing your paywalls. RevenueCat's Paywalls allow you to remotely configure your entire paywall view without any code changes or app updates.

Learn more here

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 7.0 – see Hacking with Swift tutorial 1

Similar solutions…

About the Swift Knowledge Base

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

BUY OUR BOOKS
Buy Pro Swift Buy Pro SwiftUI Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 3.0/5

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.