When added to a scroll view, this control listens to the content offset and will trigger if it's pulled past a threshold then released. Inspired by Things 3.

ScrollTriggeredControl.swift

import UIKit

class ScrollTriggeredControl: UIControl {
    private let dragThreshold: CGFloat = 80

    private var previousFraction: CGFloat = 0
    private var shouldTrigger = false
    private var offsetObservation: NSKeyValueObservation?

    private let imageView = UIImageView()
    private let impactGenerator = UIImpactFeedbackGenerator(style: .medium)

    private lazy var widthConstraint: NSLayoutConstraint = widthAnchor.constraint(equalToConstant: 0)

    init(image: UIImage?) {
        super.init(frame: .zero)

        translatesAutoresizingMaskIntoConstraints = false
        clipsToBounds = false

        addSubview(imageView)
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.image = image

        let centerConstraint = imageView.centerXAnchor.constraint(equalTo: centerXAnchor)
        centerConstraint.priority = .defaultHigh

        NSLayoutConstraint.activate([
            imageView.heightAnchor.constraint(equalTo: heightAnchor),
            imageView.centerYAnchor.constraint(equalTo: centerYAnchor),
            imageView.trailingAnchor.constraint(lessThanOrEqualTo: trailingAnchor),
            centerConstraint, widthConstraint
        ])
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func didMoveToSuperview() {
        (superview as? UIScrollView).flatMap(observe)
    }

    private func observe(scrollView: UIScrollView) {
        offsetObservation = scrollView.observe(\.contentOffset) { [weak self] scrollView, _ in
            self?.updateOffset(for: scrollView)
        }
    }

    private func updateOffset(for scrollView: UIScrollView) {
        let offset = -scrollView.adjustedContentOffset.x
        let fraction = min(offset / dragThreshold, 1)
        widthConstraint.constant = max(offset, 0)
        imageView.alpha = fraction == 1 ? 1 : 0.5 * fraction

        if shouldTrigger, !scrollView.isTracking {
            sendActions(for: .primaryActionTriggered)
            shouldTrigger = false
        }

        if fraction < 1 {
            impactGenerator.prepare()
            shouldTrigger = false
        }

        if fraction == 1, previousFraction < 1, scrollView.isTracking {
            impactGenerator.impactOccurred()
            shouldTrigger = true
        }

        previousFraction = fraction
    }
}

extension UIScrollView {
    var adjustedContentOffset: CGPoint {
        var offset = contentOffset
        offset.x += adjustedContentInset.left
        offset.y += adjustedContentInset.top
        return offset
    }
}

An example of using this control:

let menuControl = ScrollTriggeredControl(image: UIImage(named: "Large Chevron"))
menuControl.addTarget(self, action: #selector(showMenu), for: .primaryActionTriggered)
menuControl.tintColor = .white
scrollView.addSubview(menuControl)
NSLayoutConstraint.activate([
    menuControl.centerYAnchor.constraint(equalTo: scrollView.contentLayoutGuide.centerYAnchor),
    menuControl.trailingAnchor.constraint(equalTo: scrollView.contentLayoutGuide.leadingAnchor),
])

In action in Cypher: