Tiny Swift DSL for Autolayout
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
])
SwiftAutoLayout is licensed under the MIT License.