sundarsan / anchorage

A collection of operators and utilities that simplify iOS layout code.

Anchorage

A collection of intuitive operators and utilities that simplify iOS layout code. Anchorage is built directly on top of the NSLayoutAnchor API, so fully supports UILayoutGuide. Each equation or inequality acts on one or more NSLayoutAnchors, and returns active NSLayoutConstraints.

Spacing

// Pin the button to at least 12 pts from the edges of its container view, and center it
button.leftAnchor    >= container.leftAnchor + 12
button.centerXAnchor == container.centerXAnchor
button.centerYAnchor == container.centerYAnchor

// Pin all edges of a view to its container
imageView.edgeAnchors == container.edgeAnchors

// Pin only leading and trailing edges of a view to be within its container
// Note that in this case the >= is interpreted to mean "leading >=, trailing <="
imageView.horizontalAnchors >= container.horizontalAnchors

// Pin only top and bottom edges of a view to be within its container
// Note that in this case the >= is interpreted to mean "top >=, bottom <="
imageView.verticalAnchors >= container.verticalAnchors

Sizing

// Constrain a view's width to be at most 100 pts
view.widthAnchor <= 100

// Constrain two views to be the same size
view1.widthAnchor  == view2.widthAnchor
view1.heightAnchor == view2.heightAnchor

// Constrain view to 4:3 aspect ratio
view.widthAnchor == 4 * view.heightAnchor / 3

Priority

Priority of NSLayoutConstraints must be set before they are active. The ~ is used to specify priority of the constraint resulting from an equation:

// Align view 20 points from the center of its superview, with low priority
view.centerXAnchor == (view.superview.centerXAnchor + 20) ~ UILayoutPriorityDefaultLow

UIKit provides UILayoutPriorityDefaultLow, UILayoutPriorityDefaultHigh, and UILayoutPriorityRequired constants, but you may specify any Float for a priority value.