       if !switchLocked {
         let currentVc = self.children.last
         let newVc = ColorViewController()
-        newVc.color = currentVc?.view.backgroundColor == .orange ? .blue : .orange
+        newVc.color = currentVc?.view?.backgroundColor == .orange ? .blue : .orange
         self.ex.switchChilds(from: currentVc,
                              to: newVc,
                              in: self.ibExampleView,

    }
    return retValue
  }
  
  static var count: Int { return ButtonKind.switchChild.hashValue + 1 }
}

final class UIKitViewController: UIViewController {

extension UIKitViewController: UITableViewDataSource {
  
  func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return ButtonKind.allCases.count
  }
  
  func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
