UIViewController.View.Window is null in ViewDidLoad method

Question

Regardless on which controller type (UIViewController, UITableViewController), the following line always yields null in the View

Answer 1

Instead of self.view.window use

[(YourAppDelegate *)[[UIApplication sharedApplication] delegate] window]

Answer 2

According to the documentation of UIView, the window property is nil if the view has not yet been added to a window which is the case when viewDidLoad is called.

Answer 3

self.view.window will be available in viewDidAppear:

override func viewDidAppear(_ animated: Bool) {
    print(self.view.window)
    let vc = self.storyboard?.instantiateViewController(identifier: "SecondViewController") as? SecondViewController
    self.view.window?.rootViewController = vc
}