在Swift中将一行作为选择指示符添加到UITabbarItem

我解决了我的问题。

这个小代码段的功能：

• 宽度是动态的
• 它是动画的
• 它对于将来的功能更具可定制性

        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)    }    }