Using AutoLayout with UIView Subclasses in Playgrounds


Playgrounds on the Mac and iPad are a great way to develop quick prototypes for new classes. Recently I had the need to create a UIView subclass that contained a few labels. Unfortunately, I couldn’t get my labels to display in the playground. When I used a UIViewController instead of a UIView, everything displayed properly. However, when I changed the parent class to UIView and made the few appropriate changes, my background color changed but my labels no longer appeared. So, instead of seeing this:


I was seeing this:


My initial thought was to configure the label in layoutSubviews() but the result was still the same.

It turns out that the labels will not autolayout inline within the playground.  You must use the PlaygroundSupport module and the liveView window:

import UIKit
import PlaygroundSupport

class MyView: UIView {



let v = MyView(frame: CGRect(x: 0, y: 0, width: 200, height: 150))
PlaygroundPage.current.liveView = v

Here’s a complete example:

import UIKit
import PlaygroundSupport

class MyView: UIView {
    let label = UILabel()
    private func setup() {
        self.backgroundColor =

        label.translatesAutoresizingMaskIntoConstraints = false
        label.text = "Hello world"
        label.textAlignment = .center
        let margins = self.layoutMarginsGuide
        label.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: 0).isActive = true
        label.trailingAnchor.constraint(equalTo: margins.trailingAnchor, constant: 0).isActive = true
        label.topAnchor.constraint(equalTo: margins.topAnchor, constant: 0).isActive = true
        label.bottomAnchor.constraint(equalTo: margins.bottomAnchor, constant: 0).isActive = true
//    override func layoutSubviews() {
//    }
    override init(frame: CGRect) {
        super.init(frame: frame)

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")

let v = MyView(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
PlaygroundPage.current.liveView = v


Swift Cookbook Updated to Swift 3.0 Syntax

I updated my online Swift Cookbook to the 3.0 syntax.

Here are the current topics:

I also added a Github repo where all the sections are in one playground. In the near future, I hope to add sections for web, regular expressions, and files. Let me know if there are any other topics that interest you.

Functional Swift: Using Array filter and forEach functions

Recently, I started learning a couple of functional languages through online MOOCs:

Swift isn’t classified as a functional language. However, that doesn’t mean we can’t use lessons learned from functional programming to improve our code. In this article, I illustrate a few ways my programming has changed after a couple of weeks of functional programming.


There are many places in my code that looked something like this snippet:

self.retestQuestions = []

for q in questionList {
    if !q.isAnsweredCorrectly {

This translates to one line of Swift code:

let retestQuestions = questionList.filter({!$0.isAnsweredCorrectly})

In the past, I’ve used filter() to replace NSPredicate statements, which I used extensively in Objective C. In my first conversion to Swift, I directly translated my Objective C to Swift then cast my Swift array back to an NSArray to get the filter to work. Roughly my code looked like this:

let predicate = NSPredicate(format: "numWordsInGroup >= \(minWordCount) and  numPicturesInGroup >= \(minPictureCount)")

let answer = (a1 as NSArray).filtered(using: predicate)

Embracing the Array filter() function makes a lot more sense:

let answer = a1.filter({$0.numWordsInGroup >= minWordCount && $0.numPicturesInGroup >= minPictureCount})

After only a couple of weeks of functional programming, I’ve noticed many places in my code where this example, and other


The forEach() function isn’t a functional concept. However, without going into detail, my functional programming has led me to prefer using the Array forEach function more often. Here are several snippets from my code:

Add subviews to parent

[pronounView, answerWellView, answerConjugationView].forEach {self.mainContainerView.addSubview($0)}

Update: Someone pointed out on Reddit that this can be simplified:

// Simply pass func to apply to each element
[pronounView, answerWellView, answerConjugationView].forEach (mainContainerView.addSubview)

Active constraints

[c1, c2].forEach {NSLayoutConstraint.activate($0)}

Applying the same concept of passing the function as an argument to forEach(), activating constraints is even simpler.

[c1, c2].forEach(NSLayoutConstraint.activate) 

translatesAutoresizingMaskIntoConstraints and addSubviews

[answer1Btn, answer2Btn, answer3Btn, answer4Btn].forEach {
    $0.translatesAutoresizingMaskIntoConstraints = false

Disable and hide buttons

[answer1Btn,answer1Btn,answer3Btn,answer4Btn].forEach {
    $0.isEnabled = false
    $0.isHidden = false


I’ve just finished the second week, of a six week, Haskell MOOC. Hopefully, soon I’ll be using more functional concepts and my code will be “cleaner”, and more importantly contain fewer bugs.

Disabling Activity Tracing in Xcode 8

In Xcode 8, every time you run your app, there is additional logging information in the debugging window that looks similar to this:

2016-09-29 12:37:04.826400 LosVerbos[24208:17542891] subsystem:, category: HIDEventFiltered, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 1, privacy_setting: 2, enable_private_data: 0
2016-09-29 12:37:04.833232 LosVerbos[24208:17542891] subsystem:, category: HIDEventIncoming, enable_level: 0, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 1, privacy_setting: 2, enable_private_data: 0
2016-09-29 12:37:04.844944 LosVerbos[24208:17542886] subsystem:, category: MachPort, enable_level: 1, persist_level: 0, default_ttl: 0, info_ttl: 0, debug_ttl: 0, generate_symptoms: 0, enable_oversize: 0, privacy_setting: 0, enable_private_data: 0


While this may be useful at some point, I find that it makes it harder to see my own debugging messages. These messages can be disabled by setting an environment variable in your schema: OS_ACTIVITY_MODE disable


More on Apple’s new logging: WWDC 2016 – Session 721 – iOS, macOS – Unified Logging and Activity Tracing

My iOS 10 and Swift 3 Refactor List

I used an early beta of Xcode 8 to begin my conversion to Swift 3, which led to some issues so I had to do a lot of manual changes. Actually the conversion tool still works well a line at a time. Next Error followed by Return (CMD-‘, Return) is quite handy.

I thought it would be great to track them and keep a list in one place.

layerClass() method is now a variable:

override public class func layerClass() -> AnyClass {
    return CAEmitterLayer.self

override public class var layerClass: AnyClass {
    return CAEmitterLayer.self

Method signature in AppDelegate changed to:

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true

Still unresolved: ??

CGAffineTransform.scale(transform, scale, scale)
CGAffineTransform.scaledBy(transform, scale, scale) ???
transform = CGAffineTransform(scaleX: scale, y:scale)

CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0)
context.setStrokeColor(red: 1, green: 0, blue: 1, alpha: 1)
[color getRed:&red0 green:&green0 blue:&blue0 alpha:&alpha0];
       var red0:CGFloat = 0
        var green0:CGFloat = 0
        var blue0:CGFloat = 0
        var alpha0:CGFloat = 0
color.getRed(&red0, green: &green0, blue: &blue0, alpha: &alpha0)
NSMakeRange(col, 1) // Unresolved
let x = rowString.substring(with: <#T##Range#>)
UIFont *aFont = [UIFont fontWithName:"American Typewriter" size:fontSize]
let aFont = UIFont(name:"American Typewriter", size:fontSize)
NSDictionary *attributes = @{NSFontAttributeName:  aFont}
let attributes = [NSFontAttributeName:  aFont]
xmlText.components(separatedBy: "\n")
anArray.joined(separator: ",")
String(contentsOfURL: xmlUrl)
String(contentsOf: xmlUrl)
url.components(separatedBy: "/")
"  foobar  ".stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())
"  foobar  ".trimmingCharacters(in: NSCharacterSet.whitespaces)
forState: .Normal
forState: .normal
stringByReplacingOccurrencesOfString(" ", withString:"_")
"Hello, world".replacingOccurrences(of: "Hello", with: "Goodbye")
DispatchQueue.GlobalAttributes.qosDefault DispatchQoS.QoSClass.default).async {




touchesBegan() signature changed?

    override func touchesBegan(_ touches: Set, with event: UIEvent?) {
            if let touch = touches.first {
                let point = touch.location(in: self.superview)




CGContextSetLineWidth(context, 20)
self.bounds.insetBy(dx: 3, dy: 3)
self.view.bringSubview(toFront: cardFront)

self.tableView.registerClass(UITableViewCell.self, forCellReuseIdentifier:CellIdentifier)

self.tableView.register(UITableViewCell.self, forCellReuseIdentifier:CellIdentifier)

self.showViewController(viewController, sender: self), sender: self)

UIApplication.shared.openURL(URL(string: appStoreUrl)!)!, options: [:])




.dateByAddingComponents() dateComponents, to: )

Autolayout issue Xcode 8 beta 6: _SwiftValue nsli_superitem

I’m converting my Objective C and Swift 2.x code to Swift 3 and I started getting this strange error:

[_SwiftValue nsli_superitem]: unrecognized selector sent to instance 0x610000056740

This occurred in my NSLayoutConstraint.constraints() methods:

[constraintString1, constraintString2].forEach {

    let constraint = NSLayoutConstraint.constraints(withVisualFormat: $0, options: [], metrics: metrics, views: viewDictionary)



Currently, I used inferred types on my viewDictionary and metrics variables:

let viewDictionary = [
"answerView1": self.answerView1,
"answerView2": self.answerView2,
"answerView3": self.answerView3,
"answerView4": self.answerView4,

let metrics = [:]

The workaround seems to be to provide explicit types on these two variables:

let viewDictionary:[String:UIView] = [
"answerView1": self.answerView1,
"answerView2": self.answerView2,
"answerView3": self.answerView3,
"answerView4": self.answerView4,

let metrics:[String:AnyObject] = [:]

There’s probably a deeper issue here but at this point, I’m simply glad to have my app running again. I’ll post more if I figure out any additional details.

Should I Use Objective C or Swift for Writing iOS Apps?

Simply look at these code snippets:

@import UIKit; // Other imports below
#import “ViewController1.h”
#import “ViewController2.h”
#import “MyDataModel.h”
#import “NoLongerUsed.h”

NSString *s = @”Swift is the future”;
UIViewController *vc = [[UIViewController alloc] init];
UILabel *label1 = [[UILabel alloc] init];
UIButton *button1 = [[UIButton alloc] init];
NSArray *names = @[@”John”, @”Paul”, @”George”, @”Ringo”];
NSDictionary *ages = @{@”John”: @(1940), @”Paul”: @(1942), @”George”: @(1943), @”Ringo”: @(1940)};


import UIKit // No other imports needed

let s = “Swift is the future”
let vc = UIViewController()
let label1 = UILabel()
let button1 = UIButton()
let names = [“John”, “Paul”, “George”, “Ringo”]
let ages = [“John”: 1940, “Paul”: 1942, “George”: 1943, “Ringo”: 1940]

Swift is less visually noisy. Now, imagine 100,000 of code of each language. Which is more maintainable?

Less code and more maintainable code directly translates to a cost savings. The only valid argument developers have is that Swift is still an evolving language so the source will break, at least in the next version. I claim that you’re still better off writing in Swift and fixing any breaking changes than writing in Objective C. You will have done less work and your code will be safer and more maintainable.

By the way, if you want to learn Swift, there’s a lot of information available: books, blogs, and other reference material.