Playground - Testing NSLayoutConstraints

gistfile1.swift

// Playground - noun: a place where people can play

import UIKit

var base = UIView()
base.frame = CGRectMake(0, 0, 400, 500)
base.backgroundColor = UIColor.lightGrayColor()

var topImageView = UIImageView()
topImageView.setTranslatesAutoresizingMaskIntoConstraints(false)
topImageView.backgroundColor = UIColor.greenColor()



var labelA = UILabel()
labelA.setTranslatesAutoresizingMaskIntoConstraints(false)
labelA.backgroundColor = UIColor.grayColor()
labelA.text = "Label A"

var labelB = UILabel()
labelB.setTranslatesAutoresizingMaskIntoConstraints(false)
labelB.backgroundColor = UIColor.grayColor()
labelB.text = "Label B"

var labelC = UILabel()
labelC.setTranslatesAutoresizingMaskIntoConstraints(false)
labelC.backgroundColor = UIColor.grayColor()
labelC.text = "Label C"

var views = Dictionary<String, UIView>()
views["image"] = topImageView
views["labelA"] = labelA
views["labelB"] = labelB
views["labelC"] = labelC

base.addSubview(topImageView)
base.addSubview(labelA)
base.addSubview(labelB)
base.addSubview(labelC)

//Main constraints
base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-20-[image]-20-|", options: nil, metrics: nil, views: views))
base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-40-[image(80)]", options: nil, metrics: nil, views: views))

base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-20-[labelA]-20-|", options: nil, metrics: nil, views: views))
base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-20-[labelB]-20-|", options: nil, metrics: nil, views: views))
base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-20-[labelC]-20-|", options: nil, metrics: nil, views: views))

base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:[image]-20-[labelA]", options: nil, metrics: nil, views: views))

base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:[labelA]-20-[labelB]", options: nil, metrics: nil, views: views))
base.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:[labelB]-20-[labelC]", options: nil, metrics: nil, views: views))


//Fallback constraints


var constraintLabelCTop2 = NSLayoutConstraint(item: labelC, attribute: .Top, relatedBy: .Equal, toItem: labelA, attribute: .Bottom, multiplier: 1, constant: 20)
constraintLabelCTop2.priority = 100

var constraintLabelCTop3 = NSLayoutConstraint(item: labelC, attribute: .Top, relatedBy: .Equal, toItem: topImageView, attribute: .Bottom, multiplier: 1, constant: 20)
constraintLabelCTop3.priority = 100

base.addConstraint(constraintLabelCTop2)
base.addConstraint(constraintLabelCTop3)


var constraintLabelBTop2 = NSLayoutConstraint(item: labelB, attribute: .Top, relatedBy: .Equal, toItem: topImageView, attribute: .Bottom, multiplier: 1, constant: 20)
constraintLabelBTop2.priority = 100

base.addConstraint(constraintLabelBTop2)


//=============
//Tests

//labelA.removeFromSuperview()  //Uncomment
//labelB.removeFromSuperview()  //Uncomment
//labelC.removeFromSuperview()  //Uncomment

base.layoutIfNeeded()
base    // Add this to timeline