UIApplication设置了rootViewController，以在新的ViewController view.window中保持UIWindow关联

Question

我正在使用此类代码替换UIApplication窗口rootViewController

extension UIWindow {

    func set(rootViewController newViewController: UIViewController, withTransition transition: CATransition? = nil) {

        let previousViewController = self.rootViewController

        if let transition = transition {
            // Add the transition
            layer.add(transition, forKey: kCATransition)
        }

        self.rootViewController = newViewController

        // Update status bar appearance using the new view controllers appearance - animate if needed
        if UIView.areAnimationsEnabled {
            UIView.animate(withDuration: CATransaction.animationDuration()) {
                newViewController.setNeedsStatusBarAppearanceUpdate()
            }
        } else {
            newViewController.setNeedsStatusBarAppearanceUpdate()
        }

        /// The presenting view controllers view doesn't get removed from the window as its currently transistioning and presenting a view controller
        if let transitionViewClass = NSClassFromString("UITransitionView") {
            for subview in self.subviews where subview.isKind(of: transitionViewClass) {
                subview.removeFromSuperview()
            }
        }
        if let previousViewController = previousViewController {
            // Allow the view controller to be deallocated
            previousViewController.dismiss(animated: false) {
                // Remove the root view in case its still showing
                previousViewController.view.removeFromSuperview()
            }
        }
    }
}

几乎可以很好地工作，这是因为设置rootViewController不会在View Hierarchy Debugger中使ViewController重复。

但是它有一个警告，因为替换View Controller并没有关联self.view.window。没有基础窗口会导致例如view.convert（point，to：nil）不能正常工作，因为没有此窗口：/

任何帮助，为什么ViewController会丢失与窗口的关联