Introduction

What is it?

ScrollingBars make top and bottom bars follow scrollilng of a UIScrollView or similar view (e.g. UITableView or UIWebView). It works like the Safari app for iOS8.

ScrollingBars can't use with UINavigationController's navigation bar because the navigation bar provides no way to change it's height or position. It is recommended to create top bar as a generic UIView.

So what can I do with it?

Installation

Add the following to your Podfile and run $ pod install.

pod 'ScrollingBars'

If you don't have CocoaPods installed or integrated into your project, you can learn how to do so here.

Example

ScrollingBarsExample.xcworkspace in the ScrollingBarsExample directory serves as an example implementation of ScrollingBars.

Usage

Import ScrollingBars module.

import ScrollingBars

Define your view controller class with ScrollingBarsDelegate.

class YourViewController: UIViewController, ScrollingBarsDelegate {

Create outlet connections.

    @IBOutlet weak var topBar: UIView!
    @IBOutlet weak var bottomBar: UIToolbar!

    @IBOutlet weak var topBarTopSpaceConstraint: NSLayoutConstraint!
    @IBOutlet weak var bottomBarBottomSpaceConstraint: NSLayoutConstraint!

Define ScrollingBarsDelegate methods.

    // MARK: - ScrollingBarsDelegate
    
    var topBarHeight: CGFloat {
        return self.topBar.frame.size.height
    }
    
    var topBarMinHeight: CGFloat {
        if UIApplication.sharedApplication().statusBarFrame.size.height > 20  {
            // In-Call statusbar
            return 0
        } else {
            return UIApplication.sharedApplication().statusBarFrame.size.height
        }
    }

    var topBarPosition: CGFloat {
        get {
            return -self.topBarTopSpaceConstraint.constant
        }
        set {
            self.topBarTopSpaceConstraint.constant = -newValue
            // layout for animation
            self.topBar.layoutIfNeeded()
        }
    }

    var bottomBarHeight: CGFloat {
        return self.bottomBar.frame.size.height
    }
    
    var bottomBarPosition: CGFloat {
        get {
            return -self.bottomBarBottomSpaceConstraint.constant
        }
        set {
            self.bottomBarBottomSpaceConstraint.constant = -newValue
            // layout for animation
            self.bottomBar.layoutIfNeeded()
        }
    }

    var bottomBarMinHeight: CGFloat {
        return 0
    }

For the return values of theese delegate methods, see the below picture.

Call ScrollingBars's follow method in viewDidLoad (or other appropriate place), and set ScrollingBar instance to UIScrollView delegate.

    scrollingBars.follow(self.scrollView, delegate: self)
    self.scrollView.delegate = scrollingBars

    // In addition, you may need to set this.
    self.automaticallyAdjustsScrollViewInsets = false

If you can't overwrite UIScrollView delegate, pass proxy UIScrollView delegate methods manually like follows.

   func scrollViewWillBeginDragging(scrollView: UIScrollView) {
        scrollingBars.scrollViewWillBeginDragging(scrollView)
   }

    func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        scrollingBars.scrollViewDidEndDragging(scrollView, willDecelerate: decelerate)
    }

    func scrollViewDidScroll(scrollView: UIScrollView) {
        scrollingBars.scrollViewDidScroll(scrollView)
    }

    func scrollViewWillBeginDecelerating(scrollView: UIScrollView) {
        scrollingBars.scrollViewWillBeginDecelerating(scrollView)
    }

    func scrollViewShouldScrollToTop(scrollView: UIScrollView) -> Bool {
        return scrollingBars.scrollViewShouldScrollToTop(scrollView)
    }

If your view will rotate, you should probabily change the top bar height.

    override func viewWillTransitionToSize(size: CGSize, withTransitionCoordinator coordinator: UIViewControllerTransitionCoordinator) {
        coordinator.animateAlongsideTransition({ (context : UIViewControllerTransitionCoordinatorContext!) -> Void in
            self.updateTopBarHeight()
            }, completion: nil)
    }

    func updateTopBarHeight() {
        let orientation = UIApplication.sharedApplication().statusBarOrientation
        var height: CGFloat
        if orientation.isPortrait || UIDevice.currentDevice().userInterfaceIdiom == .Pad {
            height = 64
        } else {
            height = 44
        }

        let isHeightChanged = self.topBarHeightConstraint.constant != height
        if isHeightChanged {
            self.topBarHeightConstraint.constant = height
            self.topBar.layoutIfNeeded()
            self.scrollingBars.refresh(animated: false)
        }
    }

Requirements

Requires iOS 7.0, Swift.

Contributing

Forks, patches and other feedback are welcome.