拖动单元格时如何自动滚动表格视图？

Question

一旦我接近最后一个可见的单元格，如何在拖动单元格时自动向上或向下滚动表格视图？我已经尝试了很多事情，但是对于我来说，没有任何事情能顺利进行。

当我的长按手势handleLongPressChanged为gestureRecognizer.state时，将调用方法.changed。我认为这是我需要添加拖动功能的地方。我曾尝试使用scrollToRowAtIndexPath方法，但无法使其正常工作。

您将如何做？

这是我的扩展程序，用于处理用户的长按操作，该操作使用户可以拖动单元格：

import UIKit

private struct LongPressPersistentValues {
  static var indexPath: IndexPath?
  static var cellSnapShot: UIView?
}

extension CustomTableVC: UIGestureRecognizerDelegate {

  // MARK: - Long Press Setup

  func setUpTableViewLongPressGesture() {
  let longPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(handleLongPress))
  longPressGestureRecognizer.minimumPressDuration = 0.3
  longPressGestureRecognizer.delegate = self
  tableView.addGestureRecognizer(longPressGestureRecognizer)
  }

  // MARK: - Long Press Gesture Delegate Methods

  @objc func handleLongPress(_ gestureRecognizer: UIGestureRecognizer) {
      let locationInView = gestureRecognizer.location(in: self.tableView)
      let currentIndexPath = tableView.indexPathForRow(at: locationInView)

      switch gestureRecognizer.state {
      case .began:
          handleLongPressBegan(currentIndexPath, locationInView)
      case .changed:
          handleLongPressChanged(currentIndexPath, locationInView)
      case .ended:
          handleLongPressEnded()
      default:
          break
      }
  }

  // MARK: - Long Press Gesture Other Methods

  func snapshopOfCell(inputView: UIView) -> UIView {
      UIGraphicsBeginImageContextWithOptions(inputView.bounds.size, false, 0.0)
      inputView.layer.render(in: UIGraphicsGetCurrentContext()!)
      let image = UIGraphicsGetImageFromCurrentImageContext()!
      UIGraphicsEndImageContext()
      let cellSnapshot: UIView = UIImageView(image: image)
      cellSnapshot.layer.masksToBounds = false
      cellSnapshot.layer.cornerRadius = 0.0
      cellSnapshot.layer.shadowOffset = CGSize(width: -5.0, height: 0.0)
      cellSnapshot.layer.shadowRadius = 5.0
      cellSnapshot.layer.shadowOpacity = 0.4
      return cellSnapshot
  }

  func handleLongPressBegan(_ currentIndexPath: IndexPath?, _ locationInView: CGPoint) {
      let hapticGenerator = UINotificationFeedbackGenerator()
      hapticGenerator.notificationOccurred(.success)
      if currentIndexPath != nil {
          LongPressPersistentValues.indexPath = currentIndexPath
          guard let cell = tableView.cellForRow(at: currentIndexPath!) else { return }
          LongPressPersistentValues.cellSnapShot = snapshopOfCell(inputView: cell)
          var center = cell.center
          LongPressPersistentValues.cellSnapShot?.center = center
          LongPressPersistentValues.cellSnapShot?.alpha = 0.0
          tableView.addSubview(LongPressPersistentValues.cellSnapShot!)

          UIView.animate(withDuration: 0.25, animations: {
              center.y = locationInView.y
              LongPressPersistentValues.cellSnapShot?.center = center
              LongPressPersistentValues.cellSnapShot?.transform = CGAffineTransform(scaleX: 1.05, y: 1.05)
              LongPressPersistentValues.cellSnapShot?.alpha = 0.98
              cell.alpha = 0.0
          }, completion: { _ in
              cell.isHidden = true
          })
      }
  }

  func handleLongPressChanged(_ currentIndexPath: IndexPath?, _ locationInView: CGPoint) {
      var center = LongPressPersistentValues.cellSnapShot?.center
      center?.y = locationInView.y
      LongPressPersistentValues.cellSnapShot?.center = center!
      if (currentIndexPath != nil) && (currentIndexPath != LongPressPersistentValues.indexPath) {
          delegate.moveElement(from: LongPressPersistentValues.indexPath!, to: currentIndexPath!)
          tableView.moveRow(at: LongPressPersistentValues.indexPath!, to: currentIndexPath!)
          LongPressPersistentValues.indexPath = currentIndexPath
      }
  }

  func handleLongPressEnded() {
      let hapticGenerator = UIImpactFeedbackGenerator(style: .light)
      hapticGenerator.impactOccurred()
      guard let cell = tableView.cellForRow(at: LongPressPersistentValues.indexPath!) else { return }
      cell.isHidden = false
      cell.alpha = 0.0
      UIView.animate(withDuration: 0.25, animations: {
          LongPressPersistentValues.cellSnapShot?.center = cell.center
          LongPressPersistentValues.cellSnapShot?.transform = .identity
          LongPressPersistentValues.cellSnapShot?.alpha = 0.0
          cell.alpha = 1.0
      }, completion: { (finished) -> Void in
          if finished {
              LongPressPersistentValues.indexPath = nil
              LongPressPersistentValues.cellSnapShot?.removeFromSuperview()
          LongPressPersistentValues.cellSnapShot = nil
          self.tableView.reloadData()
          }
      })
  }

}