     
     open func handleScroll(in scrollView: UIScrollView) {
         setup(with: scrollView)
+        guard isSetup else { return }
         updateHeight(for: scrollView)
         updateOffset(for: scrollView)
     }

 
 If the view uses auto layout to define its height, call
 `setup(with:heightConstraint:)` once all required views
 are available. If it does not use auto layout, call the
 `setup(with:)` function instead.
 
 Once everything is setup, simply call `handleScroll(in:)`
 in the `scrollViewDidScroll(:)` delegate function. This

        return displayHeight / baseHeight
    }
    
    public var isSetup: Bool {
        return baseHeight != nil
    }
    
    public var isStretching: Bool {
        guard let view = scrollView else { return false }
        return view.contentOffset.y < -baseHeight
