TABSwiftLayout

What does it do?

A library for providing a flexible, yet very minimal API for dealing with AutoLayout programatically.

Why would I use it?

Using the standard Apple API is very cumbersome. Even something simple like constraining the width of a view:

let constraint = NSLayoutConstraint(item: view, attribute: .width, relatedBy: .equal, toItem: view, attribute: .width, multiplier: 1, constant: 100)
NSLayoutConstraint.activateConstraints([constraint])

Now with SwiftLayout:

view.size(.horizontal, relatedBy: .equal, size: 100)

As you can see, SwiftLayout also removes the need for you to activate your constraints, and removes the redundancy required in Apple's API.

What can I do with it?

Currently all the most common layout tasks can be completed with SwiftLayout.

Position:

view.pin(edge: .top, toEdge: .top, ofView: view.superview) // default margin 0
view.pin(edge: .top, toEdge: .top, ofView: view.superview, margin: 15)
view.pin(edges: [.left, .right], ofView: view.superview) // default margins (0, 0, 0, 0)
view.pin(edges: [.left, .right], ofView: view.superview, margins: EdgeMargins(top: 0, left: 15, bottom: 0, right: 15))

Sizing:

view.size(axis: .horizontal, ofViews: [view]) // default ratio 1.0
view.size(axis: .horizontal, ofViews: [view], ratio: 1.5)
view.size(axis: .horizontal, relatedBy: .equal, size: 100)
view.size(axis: .horizontal, relativeTo: .horizontal, ofView: view.superview) // default ratio 1.0
view.size(axis: .horizontal, relativeTo: .horizontal, ofView: view.superview, ratio: 0.5)

Alignment (convenience methods):

view.alignTop(toView: otherView)
view.alignBottom(toView: otherView)
view.alignLeft(toView: otherView)
view.alignRight(toView: otherView)

view.alignHorizontally(toView: otherView)
view.alignVertically(toView: otherView)

Caveats

As with Apple's API, you MUST ensure your view has been added to a superview BEFORE setting any constraints on it. However with SwiftLayout, the constraints will NOT be added in this case, and a nice print() message will indicate that you've made a mistake.

Additional API

SwiftLayout also includes an additional set of API for inspecting the types of constraints currently applied to a view.

let constraints = view.viewConstraints

This API differs slightly from Apple's implementation, since it will return automatically scan through the superview as well, in order to return ALL constraints currently being applied to this view.

let constraints = view.constraints(forTrait: .leftMargin)

This is extremely useful when you need to adjust the constant or replace a specific constraint entirely. Even better, its a bit mask, so you can request multiple constraints at once ;)

if view.contains(trait: [.leftMargin, .rightMargin]) {
  ...
}

Finally, you can also inspect a view, to determine if it contains a specific set of layout traits.