Check out example codes for "get presented view controller swift". It will help you in understanding the concepts better.

Code Example 1

// MARK: UIApplication extensions

extension UIApplication {

    class func getTopViewController(base: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {

        if let nav = base as? UINavigationController {
            return getTopViewController(base: nav.visibleViewController)

        } else if let tab = base as? UITabBarController, let selected = tab.selectedViewController {
            return getTopViewController(base: selected)

        } else if let presented = base?.presentedViewController {
            return getTopViewController(base: presented)
        }
        return base
    }
}
// How to use

if let topVC = UIApplication.getTopViewController() {
   topVC.view.addSubview(forgotPwdView)
}

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