Returns the top most child in a view controller.

UIViewController+TopMostChild.swift

import UIKit

extension UIViewController {
  var topMostChild: UIViewController? {
    if let tab = self as? UITabBarController {
      return tab.selectedViewController?.topMostChild
    } else if let nav = self as? UINavigationController {
      return nav.topViewController?.topMostChild
    } else if let split = self as? UISplitViewController {
      return split.viewControllers.last?.topMostChild
    } else if let presented = presentedViewController {
      return presented.topMostChild
    }
    return self
  }
}