Apple iOS Tutorial: Problems getting UIButton addTarget to Work - swift

Question

I am working through the "Start Developing iOS Apps" tutorial provided by Apple, and having a problem in the Implement a Custom Control section. I have tried everything to get the button to print something to the console, but can't get it to work. I am on the section in the tutorial "Add Buttons to the View" about a fifth of the way down the page.
Everything else works fine.
I have set up the RatingControl.swift file as follows:
import UIKit
class RatingControl: UIView {
// MARK: Initialisation
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
// Create a square button
let button = UIButton(frame: CGRect(x: 0, y: 0, width: 44, height: 44))
// Set the background colour of the button
button.backgroundColor = UIColor.darkGray
button.addTarget(self, action: #selector(RatingControl.ratingButtonTapped(_:)), for: .touchDown)
// Add the button to the view
addSubview(button)
}
// MARK: Button Action
func ratingButtonTapped(_: UIButton) {
print("Button pressed")
}
}
A few things there are slightly different to the tutorial, but that is because Xcode says things have changed.
In my Main.storyboard file I have added a View using the RatingControl class. The button displays but nothing happens when I click it.
Any help would be appreciated. If any extra information is needed please let me know.

Answer 1

There is actually a hierarchy of three views in this story:
A stack view (not mentioned in the original question)
The RatingControl
The button
Well, the stack view, a complicated control whose job involves a lot of voodoo with the constraints of its arranged subviews, is reducing the size of the RatingControl to zero. The button is thus outside the RatingControl's bounds (easily proved by giving the RatingControl a background color — the background color doesn't appear). The RatingControl does not clip to its bounds, so the button is still visible — but, being outside its superview, it is not tappable.
As for why the stack view is reducing the size of the RatingControl to zero: it's because the RatingControl has no intrisicContentSize. The reason why we need this is complicated and has to do with how a stack view manipulates its arranged subviews and gives them constraints. But in essence, it makes a lot of its decisions based on an arranged view's intrinsicContentSize.
In the comments you said:
In size inspector it has intrinsic size set to placeholder, width 240, height 44. Or is there something I need to do to stop the stack view making it zero sized?
The key thing to understand here is that that setting in the size inspector is only a placeholder. It is merely to shut the storyboard up so that it won't complain. It doesn't actually give the view any intrinsic size at runtime. To do that, you must actually override the intrinsicContentSize property, in your code, as a computed variable returning an actual size.

Answer 2

Looks like you're stumbling through the "Start Developing iOS Apps (Swift)" tutorial before it's updated for iOS 10 and Swift 3. Amazing you've made it this far! Anyhow, #matt has a great technical explanation below but did not include the actual code to get your tutorial working:
Add the following to your class definition (outside the init function):
override var intrinsicContentSize: CGSize {
return CGSize(width: 240, height: 44)
}

Answer 3

then your code will work : -
class RatingView: UIView {
// MARK: Initialisation
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
// Create a square button
let button = UIButton(frame: CGRect(x: 200, y: 100, width: 44, height: 44))
// Set the background colour of the button
button.backgroundColor = UIColor.darkGray
button.addTarget(self, action: #selector(self.ratingButtonTapped(_:)), for: .touchDown)
// Add the button to the view
addSubview(button)
}
// MARK: Button Action
func ratingButtonTapped(_: UIButton) {
print("Button pressed")
}
}