autolayout programmatically

translatesAutoresizingMaskIntoConstraints = false

let constraints = [
    view.centerXAnchor.constraint(equalTo: superview.centerXAnchor),
    view.centerYAnchor.constraint(equalTo: superview.centerYAnchor),
    view.widthAnchor.constraint(equalToConstant: 100),
    view.heightAnchor.constraint(equalTo: view.widthAnchor)
]
NSLayoutConstraint.activate(constraints)


NSLayoutConstraint.activate([
    view.centerXAnchor.constraint(equalTo: superview.centerXAnchor),
    view.centerYAnchor.constraint(equalTo: superview.centerYAnchor),
    view.widthAnchor.constraint(equalToConstant: 100),
    view.heightAnchor.constraint(equalTo: view.widthAnchor)
])

view 에 가능한 anchor 변수

var bottomAnchor: NSLayoutYAxisAnchor
//A layout anchor representing the bottom edge of the view’s frame.
var centerXAnchor: NSLayoutXAxisAnchor
//A layout anchor representing the horizontal center of the view’s frame.
var centerYAnchor: NSLayoutYAxisAnchor
//A layout anchor representing the vertical center of the view’s frame.
var firstBaselineAnchor: NSLayoutYAxisAnchor
//A layout anchor representing the baseline for the topmost line of text in the view.
var heightAnchor: NSLayoutDimension
//A layout anchor representing the height of the view’s frame.
var lastBaselineAnchor: NSLayoutYAxisAnchor
//A layout anchor representing the baseline for the bottommost line of text in the view.
var leadingAnchor: NSLayoutXAxisAnchor
//A layout anchor representing the leading edge of the view’s frame.
var leftAnchor: NSLayoutXAxisAnchor
//A layout anchor representing the left edge of the view’s frame.
var rightAnchor: NSLayoutXAxisAnchor
//A layout anchor representing the right edge of the view’s frame.
var topAnchor: NSLayoutYAxisAnchor
//A layout anchor representing the top edge of the view’s frame.
var trailingAnchor: NSLayoutXAxisAnchor
//A layout anchor representing the trailing edge of the view’s frame.
var widthAnchor: NSLayoutDimension
//A layout anchor representing the width of the view’s frame.

Building Constraints
func constraint(equalTo: NSLayoutAnchor<AnchorType>) -> NSLayoutConstraint
//Returns a constraint that defines one item’s attribute as equal to another.
func constraint(equalTo: NSLayoutAnchor<AnchorType>, constant: CGFloat) -> NSLayoutConstraint
//Returns a constraint that defines one item’s attribute as equal to another item’s attribute plus a constant offset.
func constraint(greaterThanOrEqualTo: NSLayoutAnchor<AnchorType>) -> NSLayoutConstraint
//Returns a constraint that defines one item’s attribute as greater than or equal to another.
func constraint(greaterThanOrEqualTo: NSLayoutAnchor<AnchorType>, constant: CGFloat) -> NSLayoutConstraint
//Returns a constraint that defines one item’s attribute as greater than or equal to another item’s attribute plus a constant offset.
func constraint(lessThanOrEqualTo: NSLayoutAnchor<AnchorType>) -> NSLayoutConstraint
//Returns a constraint that defines one item’s attribute as less than or equal to another.
func constraint(lessThanOrEqualTo: NSLayoutAnchor<AnchorType>, constant: CGFloat) -> NSLayoutConstraint
//Returns a constraint that defines one item’s attribute as less than or equal to another item’s attribute plus a constant offset.

layout guide

layoutMarginsGuide: Set constraints and keep the layout margins as spacing
readableContentGuide: Constraints the width to a size that is easy for the user to read
safeAreaLayoutGuide: Represents the portion of your view that is unobscured by bars and other content

greenView.heightAnchor.constraint(equalTo: greenView.widthAnchor, multiplier: 16/9).isActive = true