Blog - Hamburger Menu on iOS Done Right - gesturePan Selector

gesturePan Selector

@IBAction func gesturePan(_ sender: UIPanGestureRecognizer) {

      // retrieve the current state of the gesture
      if sender.state == UIGestureRecognizerState.began {

          // no need to do anything
      } else if sender.state == UIGestureRecognizerState.changed {

          // retrieve the amount viewMenu has been dragged
          let translationX = sender.translation(in: sender.view).x
          if translationX > 0 {

              // viewMenu fully dragged out
              constraintMenuLeft.constant = 0
              viewBlack.alpha = maxBlackViewAlpha
          } else if translationX < -constraintMenuWidth.constant {

              // viewMenu fully dragged in
              constraintMenuLeft.constant = -constraintMenuWidth.constant
              viewBlack.alpha = 0
          } else {

              // it's being dragged somewhere between min and max amount
              constraintMenuLeft.constant = translationX

              let ratio = (constraintMenuWidth.constant + translationX) / constraintMenuWidth.constant
              let alphaValue = ratio * maxBlackViewAlpha
              viewBlack.alpha = alphaValue
          }
      } else {

          // if the drag was less than half of it's width, close it. Otherwise, open it.
          if constraintMenuLeft.constant < -constraintMenuWidth.constant / 2 {
              self.hideMenu()
          } else {
              self.openMenu()
          }
      }
  }