Delegate is getting reset to nil - ios

Question

I have a NewCartViewController that's embedded in a UINavigationController
In my ContainerViewController:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "goToCart" {
self.cartVC = segue.destination as? NewCartViewController
self.cartVC?.delegate = self
print("cartVC Delegate", cartVC?.delegate) // value is NOT nil here
let pendingCart = PendingCart(color: .blue)
self.cartVC?.setupPaintOrder(cart: pendingCart)
}
}
In my NewCartViewController
protocol NewCartViewControllerDelegate: class {
func vcDidFinishWithCancel(_ newCartViewController: NewCartViewController)
}
class NewCartViewController: UIViewController {
weak var delegate: NewCartViewControllerDelegate?
....
#objc func dismissVC() { // called from the leftBarButtonItem
print(delegate) // nil
}
I've looked at other answers that are related but I'm not sure what's going on here. Any help would be appreciated. Thanks!
Edit - more detail on how the VC is instantiated:
My BuyButtonVC calls a delegate method back to AddToCartContainerVC:
extension AddToCartContainerViewController: BuyButtonViewControllerDelegate {
func buyButtonVCDidPressButton(_ vc: BuyButtonViewController) {
performSegue(withIdentifier: "goToCart", sender: self)
}
}
Which then fires the prepare(for segue:) function from the first code block above where the we look at the the segue.destination and set the delegate.
I have a print on the didSet on the delegate in my NewCartViewController and I see that the delegate is set.
The user goes to the screen, the didSet is never called again as if it was getting set to nil. But then when I try to call the delegate method in the second code block, the delegate is nil

Answer 1

I have tried with the following code and seems to work fine.
Few times we get this unknown behavior and is frustrating when stuck. Try to clean build and quit Xcode clear derived data and do it again.
class ContainerViewController: UIViewController, NewViewControllerDelegate {
weak var cartVC: NewViewController?
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "goToCart" {
self.cartVC = segue.destination as? NewViewController
self.cartVC?.delegate = self
print("cartVC Delegate", cartVC?.delegate) // value is NOT nil here
// let pendingCart = PendingCart(color: .blue)
// self.cartVC?.setupPaintOrder(cart: pendingCart)
}
}
func vcDidFinishWithCancel(_ newViewController: NewViewController) {
print(newViewController.delegate)
self.navigationController?.popViewController(animated: true)
}
}
protocol NewViewControllerDelegate: class {
func vcDidFinishWithCancel(_ newViewController: NewViewController)
}
class NewViewController: UIViewController {
weak var delegate: NewViewControllerDelegate?
#IBOutlet weak var leftBarButtonItem: UIBarButtonItem!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
navigationItem.leftBarButtonItem = UIBarButtonItem(title: "Cancel", style: .plain, target: self, action: #selector(dismissVC))
}
#objc func dismissVC() { // called from the leftBarButtonItem
print(delegate) // nil
delegate?.vcDidFinishWithCancel(self)
}
}
Output: when leftbarbuttonitem clicked
cartVC Delegate Optional(<NetworkExtensionTest.ViewController: 0x7f84c6d07670>)
Optional(<NetworkExtensionTest.ViewController: 0x7f84c6d07670>)
Optional(<NetworkExtensionTest.ViewController: 0x7f84c6d07670>)