Load a view controller and then remove the previous one from memory

Question

Let's say I have a view controller A (subclass of UIViewController) which has a button, and if you press the button it will load and display view controller B (subclass of UIViewController) using a segue (so I made the connection using interface builder). Segue type is Show.

When B is displayed, I will never ever go back to A, so I want to kill, destroy, crush, maim it, so that the precious few bytes of memory can be used for other things.

Here is the code for A:

class ViewControllerA: UIViewController {
  deinit {
    print("I am immortal haha I cannot die!!!")
    print("This will not be displayed!!!")
  }
}

Here is the code for B:

class ViewControllerB: UIViewController {
  override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    print("Go away old view controller!!!")
    appDelegate.window!.rootViewController = self // (1)
  }
}

My code at (1) replaced the root view controller of the app. However, the old view controller seems to linger in memory, because the print message of its deinit is not displayed.

How can I accomplish the simple task of unloading an unneeded view controller and its view? Thanks a lot

Answer 1

When you present ViewControllerB from ViewControllerA, ViewControllerB hold a strong reference of ViewControllerA in its presentingViewController variable so thats why ViewControllerA never get deinitialized. What you need to do is to change app delegates window rootViewController directly from ViewControllerA which means you must get rid of segues.