SwiftAutoLayout is a tiny DSL for Autolayout intended to provide a more declarative way to express layout constraints. Here's a quick example:
// this:
let constraint = view1.left == view2.right * 2.0 + 10.0 ~ 750
// is equivalent to:
let constraint = NSLayoutConstraint(item: view1, attribute: NSLayoutAttribute.Left, relatedBy: NSLayoutRelation.Equal, toItem: view2, attribute: NSLayoutAttribute.Right, multiplier: 2.0, constant: 10.0)
constraint.priority = 750
You may notice that this looks a lot like the linear equation that a constraint represents. From the Apple documentation:
The relationship involves a first attribute, a relationship type, and a modified second value formed by multiplying an attribute by a constant factor and then adding another constant factor to it. In other words, constraints look very much like linear equations of the following form:
attribute1 == multiplier × attribute2 + constant
SwiftAutoLayout allows you to more effectively communicate the intent of a constraint by making the syntax more similar to the equation that it represents.
Use Swift Package Manager or add SwiftAutoLayout.xcodeproj
as a subproject and link against either SwiftAutoLayout-iOS.framework
or SwiftAutoLayout-Mac.framework
depending on the platform.
Layout attributes are defined as properties added in extensions of UIView
and UILayoutGuide
on iOS and NSView
and NSLayoutGuide
on OS X. For example, UIView.width
and UIView.height
represent NSLayoutAttribute.Width
and NSLayoutAttribute.Height
, respectively.
Layout guides (conforming to UILayoutSupport
) in UIViewController
are also supported using the topLayoutGuideTop
, topLayoutGuideBottom
, bottomLayoutGuideTop
, and bottomLayoutGuideBottom
properties.
Relations are expressed using the overloaded operators ==
(NSLayoutRelation.Equal
), >=
(NSLayoutRelation.GreaterThanOrEqual
), and <=
(NSLayoutRelation.LessThanOrEqual
).
(view1.left == view2.right * 2.0 + 10.0 ~ 750).active = true
NSLayoutConstraint.activateConstraints([
view2.centerX == view2.superview!.centerX,
view2.centerY == view2.superview!.centerY,
view1.left == view2.right * 2.0 + 10.0 ~ 750,
view1.top == view2.bottom + 5.0,
view1.width >= 200,
view1.height >= 400,
view1.trailing == layoutGuide.trailing,
view2.leading == layoutGuide.leading
])
- Indragie Karunaratne
- @indragie
- http://indragie.com
SwiftAutoLayout is licensed under the MIT License.