ScrollHandling.swift

extension ViewController : UIScrollViewDelegate,UITableViewDelegate {
    
    func scrollViewWillEndDragging(scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        let yInset = scrollView.contentInset.top
        
        if scrollView.contentOffset.y > -topOffset && targetContentOffset.memory.y < -topOffset {
            targetContentOffset.memory.y = scrollView.contentOffset.y
            scrollView.setContentOffset(CGPointMake(0, -topOffset), animated: true)
        }
        else if  -topOffset > targetContentOffset.memory.y   && targetContentOffset.memory.y > (-topOffset + (topOffset - yInset)/2) {
            targetContentOffset.memory.y = scrollView.contentOffset.y
            scrollView.setContentOffset(CGPointMake(0, -topOffset), animated: true)
            
        }
        else if   (-topOffset + (topOffset - yInset)/2) > targetContentOffset.memory.y {
            targetContentOffset.memory.y = scrollView.contentOffset.y
            scrollView.setContentOffset(CGPointMake(0, -yInset), animated: true)
        }
    }
}