Swift version: 5.1
Auto Layout anchors make it easy to position your views relative to others. There are lots of anchors to choose from: leading and trailing edges, top and bottom edges, center X and center Y, and more.
To try it out, first create a view something like this:
let child = UIView() child.translatesAutoresizingMaskIntoConstraints = false child.backgroundColor = .red view.addSubview(child)
Now we can position that view by activating various anchors. For example, we could pin it to the top and bottom edges of the screen, make it precisely 128 points wide, then center it horizontally:
child.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true child.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true child.widthAnchor.constraint(equalToConstant: 128).isActive = true child.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor).isActive = true
To explore anchors further, try typing
child.anchor and exploring the code completion options.
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Available from iOS 9.0
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.