                 constant: 0
             )
             _containerView.addConstraint(_drawerConstraint)
+
+            let viewDictionary = ["drawerView" : drawerViewController.view]
             _containerView.addConstraints(
                 NSLayoutConstraint.constraintsWithVisualFormat(
                     "V:|-0-[drawerView]-0-|",

                oldController.view.removeFromSuperview()
                oldController.removeFromParentViewController()
            }
            guard let mainViewController = mainViewController else { return }
            let viewDictionary      = ["mainView" : mainViewController.view]
            mainViewController.view.translatesAutoresizingMaskIntoConstraints = false
            addChildViewController(mainViewController)
            view.insertSubview(mainViewController.view, atIndex: 0)
            view.addConstraints(
                NSLayoutConstraint.constraintsWithVisualFormat(
                    "V:|-0-[mainView]-0-|",

                    views: viewDictionary
                )
            )

            mainViewController.didMoveToParentViewController(self)
        }
    }
