extension to define contents of Navigation or Tabbar Controller

gistfile1.txt

extension UIViewController {
    var contents: UIViewController {
        if let navcon = self as? UINavigationController {
            return navcon.visibleViewController ?? self
        } else if let tabcon = self as? UITabBarController {
            return tabcon.selectedViewController ?? self
        } else {
            return self
        }
    }
}