BHMenuTransitionAnimatorPart2.swift

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
  let containerView = transitionContext.containerView
  transitionContext.viewController(forKey: .from)
  let fromVc = transitionContext.viewController(forKey: .from)!
  let toVc = transitionContext.viewController(forKey: .to)!
  let isPresenting = self.fromViewController == fromVc ? true : false
  if  isPresenting{
    let targetWidth = fromVc.view.frame.width * 0.85
    toVc.view.frame = CGRect(x: targetWidth * -1, y: 0, width: targetWidth, height: fromVc.view.frame.height)
    containerView.addSubview(toVc.view)
    UIView.animate(withDuration: 0.33, animations: {
    toVc.view.frame.origin.x = 0
    }, completion: { (isDone) in
    transitionContext.completeTransition(true)
    })
  }else {
    UIView.animate(withDuration: 0.33, animations: {
    fromVc.view.frame.origin.x = fromVc.view.frame.width * -1
    }, completion: { (isDone) in
    transitionContext.completeTransition(true )
    })
  }
}