A Swift-based DSL to make Auto Layout friendlier.
Auto Layout has gotten nice, but it can still be pretty verbose. Cully provides handy lil' helpers to reduce the amount of boilerplate code needed to layout views and dramatically improves the readability of that code.
Let's say we want to position a fixed-size
UIView in the center of another
// With `NSLayoutConstraint`s let box = UIView() view.addSubview(box) box.translatesAutoresizingMaskIntoConstraints = false NSLayoutConstraint(item: box, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 1.0, constant: 0).isActive = true NSLayoutConstraint(item: box, attribute: .centerY, relatedBy: .equal, toItem: view, attribute: .centerY, multiplier: 1.0, constant: 0).isActive = true NSLayoutConstraint(item: box, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 100).isActive = true NSLayoutConstraint(item: box, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 100).isActive = true
Woof – that's a lot to parse. The same layout with Cully:
// With Cully let box = UIView() view.addSubview(box) box.constrain(width: 100, height: 100) box.constrain(centerIn: view)
- Works directly with native types (
NSLayoutConstraint) and retains the full-power of the native API
- Adds just enough syntactic sugar to be useful, but not so much as to be overwhelming
- Reads more naturally than the native API
- Saves some time
Yes, one could use
NSLayoutAnchors, and yes, perhaps when the world is all SwiftUI this becomes less relevant, and yes, _____________________, but this is the house I built and I intend on living in it. 🏡
By default, Cully sets the receiver view's
false and activates the requested constraint.
Methods for adding constraints are namespaced
myView.constrain(bottom: .equal, .top, of: someView)
Single constraint method names mirror
NSLayoutContraint.Attributes. They all return a single
NSLayoutConstraint. Some special case convenience helpers that require creating more than one constraint return
// Singly-activated `NSLayoutConstraint`s let leftConstraint = myView.constrain(left: .equal, .left, of: someView) let baselineConstraint = myView.constrain(lastBaseline: .lessThanOrEqual, .lastBaseline, of: someView) // An array of `NSLayoutConstraint`s let dimensionConstraints = myView.constrain(width: 50, height: 80)
Methods for accessing and modifying
NSLayoutConstraints are namespaced
myView.constraints(for [.width, .height]) myView.constraints(activate: trailingConstraint)
KeyedConstraints is a typealias representing a Dictionary of
NSLayoutConstraints keyed by
let keyedConstraints = myView.constraints.keyed keyedConstraints[.width]?.constant = 150
You can also easily access the native
NSLayoutConstraint initialization API, as well as a helper on
UIView to activate and deactivate constraints.
let topConstraint = myView.constrain(.top, .equal, .top, of: view, multiplier: 1.0, constant: 100, isActive: false) ... myView.constraints(activate: topConstraint)
Cully supports the Swift Package Manager in Xcode 11. Or give Carthage a try, how 'bout?
Add the following to your
github "staykids/Cully" "1.0.1"
Cully is opinionatedly tailored to my own needs and uses, but feel free to open a pull request if you think of something cool, notice an issue, or feel something's missing.