         let left:CGFloat = width * horizontal.rawValue
         let top:CGFloat = height * vertical.rawValue
         
-        self.addChildViewController(controller)
+        addChildViewController(controller)
         
         controller.beginAppearanceTransition(
             true,

            return
        }
        
        self.addChildViewController(controller)
        
        controller.beginAppearanceTransition(
            true,

        
        currentController.removeFromParentViewController()
        
        addChildViewController(controller)
        controller.beginAppearanceTransition(true, animated:true)
        currentController.beginAppearanceTransition(false, animated:true)
        
