     func openDrawer() {
         UIView.animateWithDuration(0.3, animations: { () -> Void in
             self.leftSideConstraint.constant = 84
-            self.containerView.setNeedsLayout()
+            self.containerView.layoutIfNeeded()
         })
     }
     

                if oldVC == activeViewController {
                    return
                }
                oldVC.willMoveToParentViewController(nil)
                oldVC.view.removeFromSuperview()
                oldVC.removeFromParentViewController()
            }
            if let newVC = activeViewController {
                self.addChildViewController(newVC)
                newVC.view.frame = self.containerView.bounds
                self.containerView.addSubview(newVC.view)
                newVC.didMoveToParentViewController(self)
            }
        }
    }

    func closeDrawer() {
        UIView.animateWithDuration(0.3, animations: { () -> Void in
            self.leftSideConstraint.constant = -16
            self.containerView.layoutIfNeeded()
        })
    }
    
