BLACK FRIDAY: Save 50% on all books and bundles! >>

What’s the difference between leading, trailing, left, and right anchors?

Swift version: 5.2

Paul Hudson    @twostraws   

If you wanted to pin a button to the left edge of its parent, you might write code like this:

button.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true

However, that has a problem: in right-to-left languages, the user interface ought to be flipped horizontally for the most part, but your button won’t move – you’ve specifically asked it to be pinned to the left edge regardless of the user’s device settings.

If that’s what you want, you don’t have a problem. However, if you meant “left edge for left-to-right languages and right edge for right-to-left languages,” then you should use leadingAnchor instead of leftAnchor, like this:

button.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor).isActive = true

For the same effect on the opposite edge, you should use trailingAnchor rather than rightAnchor. Again, if you specifically want something to appear on the right regardless of language then this does not apply.

Save 50% in my Black Friday sale.

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

Available from iOS 8.0

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 Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) 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 Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 5.0/5

Link copied to your pasteboard.