Я решил свою проблему.
Особенности этого крошечного фрагмента кода:
class FirstViewController: UIViewController {
let rectShape = CAShapeLayer()
let indicatorHeight: CGFloat = 5
var indicatorWidth: CGFloat!
let indicatorBottomMargin: CGFloat = 2
let indicatorLeftMargin: CGFloat = 2
override func viewDidLoad() {
super.viewDidLoad()
// setup tabbar indicator
rectShape.fillColor = UIColor.redColor().CGColor
indicatorWidth = view.bounds.maxX / 2 // count of items
self.tabBarController!.view.layer.addSublayer(rectShape)
self.tabBarController?.delegate = self
// initial position
updateTabbarIndicatorBySelectedTabIndex(0)
}
func updateTabbarIndicatorBySelectedTabIndex(index: Int) -> Void
{
let updatedBounds = CGRect( x: CGFloat(index) * (indicatorWidth + indicatorLeftMargin),
y: view.bounds.maxY - indicatorHeight,
width: indicatorWidth - indicatorLeftMargin,
height: indicatorHeight)
let path = CGPathCreateMutable()
CGPathAddRect(path, nil, updatedBounds)
rectShape.path = path
}
}
extension FirstViewController: UITabBarControllerDelegate {
func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
updateTabbarIndicatorBySelectedTabIndex(tabBarController.selectedIndex)
}
}