Swift: Change value of another ViewController with delegation programmatically - ios

Question

I am trying to change the value of one ViewController by clicking a button inside a second ViewController with delegation.
But so far it only prints a message, but doesn't change the value.
I have this class where I defined a view:
class CounterView: UIView {
public var creditPointValue = Int()
let label = UILabel()
override init(frame: CGRect) {
super.init(frame: frame)
self.translatesAutoresizingMaskIntoConstraints = false
backgroundColor = .cyan
self.addSubview(label)
label.text = "Credit Points: \(creditPointValue)"
label.translatesAutoresizingMaskIntoConstraints = false;
label.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
label.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
}
func changeCreditPointValue(value:Int){
creditPointValue = creditPointValue + value
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
I am using that view inside this ViewController and I want to manipulate the variable "creditPointValue":
protocol AddCreditsDelegate {
func addCreditsToCounter()
}
class ViewController: UIViewController {
var delegate: AddCreditsDelegate?
var counterView = CounterView()
let label = UILabel()
let button = UIButton(frame: CGRect(x: 100, y: 100, width: 100, height: 50))
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
view.backgroundColor = .white
view.addSubview(button)
button.backgroundColor = .red
button.setTitle("View2", for: .normal)
button.translatesAutoresizingMaskIntoConstraints = false
button.addTarget(self, action: #selector(changeView), for: .touchUpInside)
button.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
button.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
}
override func viewDidAppear(_ animated: Bool) {
view.addSubview(counterView)
counterView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
counterView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
counterView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
//counterView.frame.size.height = 30
counterView.bottomAnchor.constraint(equalTo: counterView.topAnchor, constant: 50).isActive = true
}
#objc func changeView(){
delegate?.addCreditsToCounter()
navigationController?.pushViewController(ViewController2(), animated: true)
}
}
And inside this second ViewController I am trying to change the value by clicking the button I added to the view:
class ViewController2: UIViewController {
let button = UIButton(frame: CGRect(x: 100, y: 100, width: 100, height: 50))
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
view.addSubview(button)
button.backgroundColor = .red
button.setTitle("add Credits", for: .normal)
button.translatesAutoresizingMaskIntoConstraints = false
button.addTarget(self, action: #selector(addCreditsButton), for: .touchUpInside)
button.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
button.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
}
#objc func addCreditsButton(){
addCreditsToCounter()
}
}
extension ViewController2 : AddCreditsDelegate{
func addCreditsToCounter() {
let vc = ViewController()
vc.delegate = self
vc.counterView.creditPointValue += 5
print("pressed")
}
}
So far only the message "pressed" gets printed each time I click the button and I don't even know if I am going into the right direction with my approach trying to use delegation.

Answer 1

You should not create a new ViewController instance each time you call ViewController2.addCreditsToCounter, you already have a ViewController that creates a ViewController2 instance in ViewController.changeView. Just store a weak reference to ViewController in ViewController2 using delegate. In such case ViewController (not ViewController2) should conform to AddCreditsDelegate.
First of all, replace
protocol AddCreditsDelegate {
func addCreditsToCounter()
}
with
protocol AddCreditsDelegate: AnyObject {
func addCreditsToCounter()
}
Then add weak var delegate: AddCreditsDelegate? to ViewController2 and remove ViewController.delegate. Remove ViewController2.addCreditsToCounter, ViewController2 should not conform to AddCreditsDelegate. It means that in ViewController2.addCreditsButton you should call delegate?.addCreditsToCounter(), not addCreditsToCounter().
ViewController should conform to AddCreditsDelegate:
extension ViewController: AddCreditsDelegate {
func addCreditsToCounter() {
counterView.creditPointValue += 5
print("pressed")
}
}
And don't forget to initialize ViewController2.delegate. Replace your ViewController.changeView implementation with
let controller = ViewController2()
controller.delegate = self
navigationController?.pushViewController(controller, animated: true)

Answer 2

You create a new instance here
let vc = ViewController()
instead you need
#objc func changeView() {
let sec = ViewController2(),
sec.delegate = self
navigationController?.pushViewController( animated: true)
}
Then declare this inside the SecondVC
weak var delegate:ViewController?
Finally
func addCreditsToCounter() {
delegate?.counterView.creditPointValue += 5
print("pressed")
}