Swapping rootViewController on UIWindow does not deallocate view controller

Question

If you swap out a rootViewController in UIWindow, for example, to present a log in window, if the rootViewController has presented (modal) view controllers, those presented view controllers and possibly the old rootViewController will not be deallocated.

self.window.rootViewController = newViewController

Answer 1

You must always do a dismissal of all modals when swapping out the rootViewController, otherwise there will be a retain cycle.

if window?.rootViewController.presentedViewController != nil {
    window?.rootViewController.dismiss?(animated: false) {
        window?.rootViewController = newViewController
    }
}
else {
    window?.rootViewController.dismiss?(animated: false)
    window?.rootViewController = newViewController
}

If you want to do a nice transition, you could always wrap it in an animation:

func transition() {
    if window?.rootViewController.presentedViewController != nil {
        window?.rootViewController.dismiss?(animated: false) {
            window?.rootViewController = newViewController
        }
    }
    else {
        window?.rootViewController.dismiss?(animated: false)
        window?.rootViewController = newViewController
    }
}

UIView.transition(with: window!,
                  duration: 0.3,
                  options: .transitionCrossDissolve,
                  animations: transition)