Adjust the size UIView to accommodate the size of its content in Swift

ViewController.swift

//
//  ViewController.swift
//  sizingTest
//
//  A Swift version of John Erck's SO answer:
//  http://stackoverflow.com/a/30511982/131385
//

import UIKit

class ViewController: UIViewController {

    var contentView: UIView = UIView()
    var myOtherLabel: UILabel = UILabel()
    var myLabel: UILabel = UILabel()
    
    override func viewDidLoad() {
        super.viewDidLoad()

        // INIT ALL REQUIRED UI ELEMENTS
        let viewsDictionary = ["contentView": contentView, "myLabel": myLabel, "myOtherLabel": myOtherLabel]

        // TURN AUTO LAYOUT ON FOR EACH ONE OF THEM
        self.contentView.translatesAutoresizingMaskIntoConstraints = false
        self.myLabel.translatesAutoresizingMaskIntoConstraints = false
        self.myOtherLabel.translatesAutoresizingMaskIntoConstraints = false
        
        // ESTABLISH VIEW HIERARCHY
        self.view.addSubview(self.contentView) // View adds content view
        self.contentView.addSubview(self.myLabel) // Content view adds my label (and all other UI... what's added here drives the container height (and width))
        self.contentView.addSubview(self.myOtherLabel)
        
        // LAYOUT
        
        // Layout CONTENT VIEW (Pinned to left, top. Note, it expects to get its vertical height (and horizontal width) dynamically based on whatever is placed within).
        // Note, if you don't want horizontal width to be driven by content, just pin left AND right to superview.
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|[contentView]", options:.DirectionLeadingToTrailing, metrics:nil, views:viewsDictionary)) // Only pinned to left, no horizontal width yet
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|[contentView]", options:.DirectionLeadingToTrailing, metrics:nil, views:viewsDictionary)) // Only pinned to top, no vertical height yet
        
        /* WHATEVER WE ADD NEXT NEEDS TO EXPLICITLY "PUSH OUT ON" THE CONTAINING CONTENT VIEW SO THAT OUR CONTENT DYNAMICALLY DETERMINES THE SIZE OF THE CONTAINING VIEW */
        // ^To me this is what's weird... but okay once you understand...
        
        // Layout MY LABEL (Anchor to upper left with default margin, width and height are dynamic based on text, font, etc (i.e. UILabel has an intrinsicContentSize))
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-[myLabel]", options:.DirectionLeadingToTrailing, metrics:nil, views:viewsDictionary))
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-[myLabel]", options:.DirectionLeadingToTrailing, metrics:nil, views:viewsDictionary))
        
        // Layout MY OTHER LABEL (Anchored by vertical space to the sibling label that comes before it)
        // Note, this is the view that we are choosing to use to drive the height (and width) of our container...
        
        // The LAST "|" character is KEY, it's what drives the WIDTH of contentView (red color)
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-[myOtherLabel]-|", options:.DirectionLeadingToTrailing, metrics:nil, views:viewsDictionary))
        
        // Again, the LAST "|" character is KEY, it's what drives the HEIGHT of contentView (red color)
        self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:[myLabel]-[myOtherLabel]-|", options:.DirectionLeadingToTrailing, metrics:nil, views:viewsDictionary))
        
        // COLOR VIEWS
        self.view.backgroundColor = UIColor.purpleColor()
        self.contentView.backgroundColor = UIColor.redColor()
        self.myLabel.backgroundColor = UIColor.orangeColor()
        self.myOtherLabel.backgroundColor = UIColor.greenColor()
        
        // CONFIGURE VIEWS
        
        // Configure MY LABEL
        self.myLabel.text = "HELLO WORLD\nLine 2\nLine 3, yo"
        self.myLabel.numberOfLines = 0; // Let it flow
        
        // Configure MY OTHER LABEL
        self.myOtherLabel.text = "My OTHER label... This\nis the UI element I'm\narbitrarily choosing\nto drive the width and height\nof the container (the red view)"
        self.myOtherLabel.numberOfLines = 0;
        self.myOtherLabel.font = UIFont.systemFontOfSize(21.0)

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}