PullToDismiss.swift

override func viewDidLoad() {
    super.viewDidLoad()
    isModalInPresentation = true
    navigationController?.presentationController?.delegate = self
}

/// conforming to UIAdaptivePresentationControllerDelegate
func presentationControllerDidAttemptToDismiss(_ presentationController: UIPresentationController) {
    let controller = UIAlertController(title: nil, message: nil, preferredStyle: .actionSheet)
    // ...
    present(controller, animated: true)
}