     public init(scrollView: UIScrollView, viewController: UIViewController, navigationBar: UIView? = nil) {
         super.init()
         scrollView.delegate = self
+        __scrollView = scrollView
         self.viewController = viewController
         if let navigationBar = navigationBar ?? viewController.navigationController?.navigationBar {
             let gesture = UIPanGestureRecognizer(target: self, action: #selector(handlePanGesture(_:)))

        if let panGesture = panGesture {
            panGesture.view?.removeGestureRecognizer(panGesture)
        }
    }
    
    fileprivate var targetViewController: UIViewController? {

    fileprivate var previousContentOffsetY: CGFloat = 0.0
    fileprivate weak var viewController: UIViewController?
    
    private var __scrollView: UIScrollView?
    private var panGesture: UIPanGestureRecognizer?
    private var backgroundView: UIView?
    private var navigationBarHeight: CGFloat = 0.0
