A swift pan gestureRecognizer that can discriminate in a particular direction. Useful for views requiring (for example) horizontal pan support nested inside a uiscrollview (for example)

DSFRestrictedPanGestureRecognizer.swift

//
//  DSFRestrictedPanGestureRecognizer.swift
//  Time Zones
//
//  Created by Darren Ford on 30/6/18.
//  Copyright © 2018 Darren Ford. All rights reserved.
//

import UIKit
import UIKit.UIGestureRecognizerSubclass

class DSFRestrictedPanGestureRecognizer: UIPanGestureRecognizer {
   let kDirectionPanThreshold: CGFloat = 2.0;

   public enum RestrictTo {
      case vertical
      case horizontal
   }

   var _drag: Bool = false
   var _moveX: CGFloat = 0
   var _moveY: CGFloat = 0
   public var direction: RestrictTo = .vertical

   override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent) {
      super.touchesMoved(touches, with: event)
      if self.state == .failed {
         return
      }

      guard let touch = touches.first else {
         return
      }

      let nowPoint = touch.location(in: self.view!)
      let prevPoint = touch.previousLocation(in: self.view!)
      _moveX = prevPoint.x - nowPoint.x
      _moveY = prevPoint.y - nowPoint.y
      if !_drag {
         if fabs(_moveX) > kDirectionPanThreshold {
            if self.direction == .vertical {
               self.state = .failed
            }
            else {
               _drag = true
            }
         }
         else if fabs(_moveY) > kDirectionPanThreshold {
            if self.direction == .horizontal {
               self.state = .failed
            }
            else {
               _drag = true
            }
         }
      }
   }

   override func reset() {
      super.reset()
      _drag = false
      _moveX = 0
      _moveY = 0
   }
}