Registers scroll view and label to navigation bar. Title attachs the navigation bar if scrolled out of screen

UIViewController+NavigationBarScrollingTitleView

private var UIViewControllerRegisteredLabel: UInt8 = 0
private var UIViewControllerScrollTitleLabel: UInt8 = 1
extension UIViewController {
    
    private var registeredLabel: UILabel? {
        get {
            return objc_getAssociatedObject(self, &UIViewControllerRegisteredLabel) as? UILabel
        } set (value) {
            objc_setAssociatedObject(self, &UIViewControllerRegisteredLabel, value, UInt(OBJC_ASSOCIATION_RETAIN_NONATOMIC))
        }
    }
    
    private var scrollTitleLabel: UILabel? {
        get {
            return objc_getAssociatedObject(self, &UIViewControllerScrollTitleLabel) as? UILabel
        } set (value) {
            objc_setAssociatedObject(self, &UIViewControllerScrollTitleLabel, value, UInt(OBJC_ASSOCIATION_RETAIN_NONATOMIC))
        }
    }
    
    func registerScrollLabel (scroll: UIScrollView, label: UILabel) {
        
        if let nav = navigationController {
            registeredLabel = label
            
            let container = UIView (frame: nav.navigationBar.frame)
            container.y -= UIScreen.StatusBarHeight
            container.clipsToBounds = true
            container.tag = 10
            nav.navigationBar.addSubview(container)
            
            scrollTitleLabel = UILabel (frame: container.frame)
            scrollTitleLabel?.text = label.text
            scrollTitleLabel?.textColor = label.textColor
            scrollTitleLabel?.textAlignment = .Center
            container.addSubview(scrollTitleLabel!)
            
            scroll.addObserver(self, forKeyPath: "contentOffset", options: .New, context: nil)
        }
    }
    
    public override func observeValueForKeyPath(
        keyPath: String,
        ofObject object: AnyObject,
        change: [NSObject : AnyObject],
        context: UnsafeMutablePointer<Void>) {
     
        let container = navigationController!.navigationBar.viewWithTag(10)!
        let scroll = object as! UIScrollView
        let position = scroll.convertPoint(registeredLabel!.frame.origin, toView: container)
            
        let targetY = position.y +
                        scroll.contentInset.top -
                        registeredLabel!.frame.size.height -
                        scrollTitleLabel!.frame.size.height
        let maxY =  container.frame.size.height -
                    scrollTitleLabel!.frame.size.height
            
        let y = max (targetY, maxY)
        scrollTitleLabel?.frame.origin.y = y
    }
}

Example usage

class ViewController: UIViewController {

    var scroll: UIScrollView!

    override func viewDidLoad() {
        scroll = UIScrollView (frame: view.frame)
        view.addSubview(scroll)

        let label = UILabel (
            x: 10,
            y: 50,
            text: "Some Label",
            textColor: UIColor.blackColor(),
            textAlignment: .Left,
            font: UIFont.systemFontOfSize(15))
        scroll.addSubview(label)
        scroll.contentHeight = label.bottomWithOffset(10)

        for _ in 0...20 {
            scroll.addSubview(item (scroll.contentHeight))
            scroll.contentHeight += 160
        }

        let tit = UIView (x: 0, y: 0, w: 35, h: 30)
        tit.backgroundColor = UIColor.redColor()
        navigationItem.titleView = tit

        self.registerScrollLabel(scroll, label: label)
    }

    func item (y: CGFloat) -> UIView {
        let v = UIView (frame: CGRect (x: 10, y: y, width: view.w - 20, height: 150))
        v.backgroundColor = UIColor.randomColor()
        return v
    }
}