A UIScrollView subclass that honours the reduce motion accessibility setting

ReduceMotionScrollView.swift

// Douglas Hill, October 2018

import UIKit

/**
 A scroll view that honours the reduce motion accessibility setting.

 If reduce motion is enabled, animated adjustments to contentOffset
 will use a cross dissolve instead of translation.

 This  does not handle scrolling to the top when tapping the status bar.
 To use a cross dissolve for that, the scroll view’s delegate must
 implement scrollViewShouldScrollToTop: by scrolling to the top manually
 and returing false.
 */
class ReduceMotionScrollView: UIScrollView {
    override func setContentOffset(_ newContentOffset: CGPoint, animated: Bool) {
        guard
            animated,
            UIAccessibility.isReduceMotionEnabled,
            let superview = superview,
            let snapshot = self.snapshotView(afterScreenUpdates: false) else
        {
            super.setContentOffset(newContentOffset, animated: animated)
            return
        }

        snapshot.frame = frame
        superview.insertSubview(snapshot, aboveSubview: self)

        super.setContentOffset(newContentOffset, animated: false)

        UIView.transition(with: superview, duration: 0.2, options: .transitionCrossDissolve, animations: {
            snapshot.removeFromSuperview()
        }, completion: nil)
    }
}