Reverse Animation Alternative

    UIView.animateKeyframesWithDuration(0.6, delay: 0.0, options: UIViewKeyframeAnimationOptions.CalculationModeLinear, animations: {
      UIView.setAnimationRepeatCount(3);

      self.myconstraint.constant = 40
      UIView.addKeyframeWithRelativeStartTime(0.0, relativeDuration: 0.3, animations: {
        self.view.layoutIfNeeded()
      })

      self.myconstraint.constant = 30
      UIView.addKeyframeWithRelativeStartTime(0.3, relativeDuration: 0.3, animations: {
        self.view.layoutIfNeeded()
      })
    }, completion: nil)