Delegate function not called - ios

Question

I have two view controllers (ViewController and ActionViewController) and one manager (Brain), the second view controller is shown when a user tapped on a button by a show segue created in storyboard and to get back to the first I use a self.dismiss in the second view controller.
The user enter a number on ActionViewController that need to be retrieved in ViewController. So I created Brain to use the delegate pattern.
The problem is that the delegate function inside ViewController is never run, I read other SO answers but nothing work. I used print statement to know where the code is not running anymore and the only block not running is the didUpdatePrice inside ViewController
Here is the code
ViewController
class ViewController: UIViewController, BrainDelegate {
var brain = Brain()
#IBOutlet var scoreLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
brain.delegate = self
scoreLabel.layer.cornerRadius = 25
scoreLabel.layer.masksToBounds = true
}
func didUpdateScore(newScore: String) {
print("the new label is \(newScore)")
scoreLabel.text = newScore
}
}
ActionViewController
class ActionViewController: UIViewController {
var brain = Brain()
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func addButtonTapped(_ sender: Any) {
brain.newAction(actualScore: 0, newActionValue: 5, isPositive: true)
self.dismiss(animated: true)
}
}
Brain
protocol BrainDelegate {
func didUpdateScore(newScore: String)
}
struct Brain {
var delegate: BrainDelegate?
func newAction(actualScore: Int, newActionValue: Int, isPositive: Bool) {
let newScore: Int
if isPositive {
newScore = actualScore + newActionValue
} else {
newScore = actualScore - newActionValue
}
print("the new score is \(newScore)")
delegate?.didUpdateScore(newScore: String(newScore))
}
}

Answer 1

You dont need an additional Brain class/struct at all, You can achieve it with simple protocol and default extension of protocol.
Step 1: Select your show segue and provide an identifier to that in storyboard as shown below
Step 2: In your ViewController add prepare(for segue method
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "testIdentifier" {
guard let destinationViewController = segue.destination as? ActionViewController else { return }
destinationViewController.delegate = self
}
}
Step 3: In your ActionViewController declare a weak property named delegate
class ActionViewController: UIViewController {
weak var delegate: BrainDelegate? = nil
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func addButtonTapped(_ sender: Any) {
delegate?.newAction(actualScore: 0, newActionValue: 5, isPositive: true)
self.dismiss(animated: true)
}
}
Step 4: Add class clause to your BrainDelegate (Class bound protocol) so that you can hold a weak reference to delegate
protocol BrainDelegate: class {
func didUpdateScore(newScore: String)
func newAction(actualScore: Int, newActionValue: Int, isPositive: Bool)
}
Step 5:
Add a default extension to BrainDelegate and provide default implementation of newAction(actualScore:
extension BrainDelegate {
func newAction(actualScore: Int, newActionValue: Int, isPositive: Bool) {
let newScore: Int
if isPositive {
newScore = actualScore + newActionValue
} else {
newScore = actualScore - newActionValue
}
print("the new score is \(newScore)")
self.didUpdateScore(newScore: String(newScore))
}
}
Step 6: In your ActionViewController simply trigger delegate methods as
#IBAction func addButtonTapped(_ sender: Any) {
delegate?.newAction(actualScore: 0, newActionValue: 5, isPositive: true)
self.dismiss(animated: true)
}
This should do the job

Answer 2

First, on Brain you should use class, not struct. That is because when you use struct, passing the variable to another will make a copy, it will not use the same reference. And class will only copy the reference.
That means that your Brain struct will lose the delegate assigned on .delegate = self
second, you need to use the same instance on the second viewController and the first. like this:
on the first viewController
var brain = Brain()
// this one is the one that you will put your "brain.delegate = self"
on the second viewController, you will need to inject this variable from the first viewController into the second. That is to keep the same instance on both. And this will make the delegate callable.
to do this with storyboard you will do on the first ViewController:
// this function should be called when the next viewController should open.
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
switch segue.destination) {
case let vc as MyViewController:
vc.brain = self.brain
default:
break
}
}
super.prepare(for: segue, sender: sender)
}
inside the second viewController, use:
var brain: Brain?