             if vc == nil {
                 
                 vc = storyboard.instantiateViewController(withIdentifier: "ChildViewController2") as? PageViewController
+                vc?.identifier = "ChildViewController2"
             }
             
         } else {

            if vc == nil {
             
                vc = storyboard.instantiateViewController(withIdentifier: "ChildViewController1") as? PageViewController
            }
            
        } else if index == 1 {

            if vc == nil {
                
                vc = storyboard.instantiateViewController(withIdentifier: "ChildViewController3") as? PageViewController
                vc?.identifier = "ChildViewController3"
            }
            
        }
