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Anchora

A small framework that abstracts over UIKit's Auto Layout engine in a native style to tidy up your constraints.

Usage

Each constraint is a linear equation with the following format:

item1.attribute1 = multiplier * item2.attribute2 + constant

Anchora makes use of this equation to provide a convenient and intuitive way of building constraints in a native style.

Single constraints are constructed using the following methods: equals(_:), lessOrEquals(_:), greaterOrEquals(_:), each of which represents a layout relation and takes a single expression of the following format, where multiplier and constant are optional:

anchor [* or /] multiplier [+ or -] constant

For instance,

view1.centerXAnchor.equals(view2.centerXAnchor * 2 + 10)

view1.rightAnchor.lessOrEquals(view2.leftAnchor - 8)

view1.heightAnchor.equals(view2.heightAnchor)

As an exception, NSLayoutDimension constraints can simply take a number.

view.widthAnchor.equals(80)

Anchor Groups

Apart from the existing anchors we all know, Anchora comes with some built-in anchor groups that serve a great means of brevity when constructing several related constraints at once. The order in the list of anchors a group represents matters!

  • centerAnchors == (centerXAnchor, centerYAnchor)
  • sizeAnchors == (widthAnchor, heightAnchor)
  • edgeAnchors == (topAnchor, leftAnchor, bottomAnchor, rightAnchor)

The constrain(...) method allows to create constraints by associating a set of individual anchors to their equivalents in the anchor group, while equal(_:) is the bulk variant of equals(_:) for an individual anchor.

view1.edgeAnchors.equal(view2.edgeAnchors)

// Equivalent to
view1.topAnchor.equals(view2.topAnchor)
view1.leftAnchor.equals(view2.leftAnchor)
view1.bottomAnchor.equals(view2.bottomAnchor)
view1.rightAnchor.equals(view2.rightAnchor)
view1.sizeAnchors.equal(100)

// Equivalent to
view1.widthAnchor.equals(100)
view1.heightAnchor.equals(100)
view1.centerAnchors.constrain(view2.centerXAnchor - 10, view2.centerYAnchor) 

// Equivalent to
view1.centerXAnchor.equals(view2.centerXAnchor - 10)
view1.centerYAnchor.equals(view2.centerYAnchor)

For convenience, Anchora methods return discardable active constraints. If you need an inactive constraint, use inactive().

let constraint = view1.rightAnchor.equals(view2.leftAnchor - 8).inactive()

Requirements

  • Xcode 9 +
  • Swift 4 +
  • iOS 10 +

Installation

You can integrate Anchora with CocoaPods. Add it to your Podfile and run $ pod install.

platform :ios, '10.0'
use_frameworks!

target '<Your Target>' do
    pod 'Anchora'
end