NSLayoutConstraint playground test

nslayoutconstraint_test.swift

// how to programatically create NSLayoutConstraints inside a playground

import UIKit

let viewFrame = CGRect(x: 0, y: 0, width: 640, height: 750)
let view = UIView(frame: viewFrame)
view.backgroundColor = UIColor.greenColor()

// initially the subView will obscure the entire view
let subView = UIVisualEffectView(effect: UIBlurEffect(style: UIBlurEffectStyle.Dark))
subView.backgroundColor = UIColor.redColor()

view.addSubview(subView)

// Align the top of the subView to the top of its parent view
let topConstraint = NSLayoutConstraint(
    item: subView,
    attribute: NSLayoutAttribute.Top,
    relatedBy: NSLayoutRelation.Equal,
    toItem: subView.superview,
    attribute: NSLayoutAttribute.Top,
    multiplier: 1,
    constant: 0
)

// Align the leading (left) edge to the leading (left) edge of its parent view
let leadingConstraint = NSLayoutConstraint(
    item: subView,
    attribute: NSLayoutAttribute.Leading,
    relatedBy: NSLayoutRelation.Equal,
    toItem: subView.superview,
    attribute: NSLayoutAttribute.Leading,
    multiplier: 1,
    constant: 0
)

// Align the trailing (right) edge to the trailing (right) edge of its partent view
let trainlingConstraint = NSLayoutConstraint(
    item: subView,
    attribute: NSLayoutAttribute.Trailing,
    relatedBy: NSLayoutRelation.Equal,
    toItem: subView.superview,
    attribute: NSLayoutAttribute.Trailing,
    multiplier: 1,
    constant: 0
)

// Give the subView a constant height of 64 points. Not the special "NotAnAttribute"
let heightConstraint = NSLayoutConstraint(
    item: subView,
    attribute: NSLayoutAttribute.Height,
    relatedBy: NSLayoutRelation.Equal,
    toItem: nil,
    attribute: NSLayoutAttribute.NotAnAttribute,
    multiplier: 1,
    constant: 64
)

subView.setTranslatesAutoresizingMaskIntoConstraints(false)

view.addConstraint(topConstraint)
view.addConstraint(leadingConstraint)
view.addConstraint(trainlingConstraint)
view.addConstraint(heightConstraint)
// This is necessary to force autolayout to reposition the views
view.layoutIfNeeded()

view