view controller's navigation controller property is nil after being pushed

Question

I am trying to understand why a) vc2's navController property is nil, and b) why the nav controller vc stack does not have vc2.

import UIKit

let vc1 = UIViewController()

let navController1 = UINavigationController(rootViewController: vc1)

print(navController1.viewControllers) // prints vc1
print(vc1.navigationController) // prints navController1

let vc2 = UIViewController()

navController1.pushViewController(vc2, animated: true)

print(navController1.viewControllers) // prints only vc1. Hmmm

print(vc2.navigationController) // prints nil

Answer 1

Timing...

let vc1 = UIViewController()

let navController1 = UINavigationController(rootViewController: vc1)

print(navController1.viewControllers) // prints vc1
print(vc1.navigationController) // prints navController1

let vc2 = UIViewController()

// animated: true !!!!
navController1.pushViewController(vc2, animated: true)

// next two lines execute BEFORE the above line finishes
print(navController1.viewControllers) // prints only vc1. Hmmm

print(vc2.navigationController) // prints nil

Change animated to false:

// animated: false !!!!
navController1.pushViewController(vc2, animated: false)

and you'll see what you were expecting to see.