UIViewController's delegate var becomes nil - ios

Question

I have already read all articles but could not find a solution. I have a class to organize navigation between controllers:
class Navigator: NotesListViewControllerDelegate {
var rootController:UINavigationController!
lazy private var notesListController:NotesListViewController! = {
let controller = NotesListViewController(nibName: String(NotesListViewController), bundle: nil)
controller.title = "Notes"
return controller
}()
init() {
self.rootController = UINavigationController.init(rootViewController: self.notesListController)
self.notesListController.delegate = self
}
//MARK: NotesListController delegate
func plusButtonDidSelect() {
print("plus button did select")
}
}
My NotesListController:
protocol NotesListViewControllerDelegate:class {
func plusButtonDidSelect()
}
class NotesListViewController: UIViewController {
weak var delegate:NotesListViewControllerDelegate? {
didSet {
print("delegate = \(delegate)")
}
}
System shows in didSet what variable has setted. But in viewDidLoad self.delegate is already has nil value. What could be a problem?
EDIT: my didFinishLaunchingWithOptions method:
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
self.window = UIWindow.init(frame: UIScreen.mainScreen().bounds)
let navigator = Navigator()
if let window = self.window {
window.backgroundColor = UIColor.whiteColor()
window.rootViewController = navigator.rootController
window.makeKeyAndVisible()
}
return true
}
EDIT 2 I resolved this problem by taking out navigator variable from didFinishLaunchingWithOptions method to other class variables (it becomes like strong property in obj-c). But why system not keeps it in memory when it was declared localy in didFinishLaunchingWithOptions method?

Answer 1

What is maintaining a reference to your Navigator instance ?
The NotesListViewController instance only has a weak reference so if nothing else keeps the Navigator alive, it will go out of scope and the delegate variable will go nil in notesListController (which I assume is being referenced elsewhere because it is being presented)