Swift自定义iOS中的TabBarController并为其添加动画

    // 声明新的无标题TabBarItem    
    let tabBarItem = UITabBarItem(title: nil, image: image, selectedImage: selectedImage)
    // 设置 tabBarItem 的 imageInsets 可以使图标居中显示
    tabBarItem.imageInsets = UIEdgeInsetsMake(6, 0, -6, 0)

    viewController.tabBarItem = tabBarItem
}

// 用记录下的frame建立一个UIView
let myView = UIView(frame: rect)
// 设置这个View的背景色
myView.backgroundColor = UIColor(patternImage: UIImage(named: "TabBarBG")!)
self.view.addSubview(myView)

for var i = 0; i < self.viewControllers?.count; i++ {

    let button = UIButton()

    // 根据子ViewController的个数计算Button的宽度
    let width = myView.frame.size.width / CGFloat(self.viewControllers!.count)
    let x = CGFloat(i) * width
    button.frame = CGRectMake(x, 0, width, myView.frame.size.height)

    // 设置Button未选中时候的图标
    let image = UIImage(named: "TabBar\(i)")?.imageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal)
    button.setImage(image, forState: UIControlState.Normal)

    // 设置Button选中时候的图标，注意这里Button的状态是Selected，而不是Highlighted
    let selImage = UIImage(named: "TabBar\(i)Sel")?.imageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal)
    button.setImage(selImage, forState: UIControlState.Selected)

    // 设置Button未选中和选中时候的背景图
    button.setBackgroundImage(UIImage(named: "TabBarBG"), forState: UIControlState.Normal)
    button.setBackgroundImage(UIImage(named: "TabBarBGSel"), forState: UIControlState.Selected)

    // 去掉UIButton自带的高光效果
    button.adjustsImageWhenHighlighted = false

    myView.addSubview(button)

    // 设置UIButton的标记
    button.tag = i

    button.addTarget(self, action: "onClick:", forControlEvents: UIControlEvents.TouchUpInside)

    // 设置默认的选中项
    if i == 0 {
        button.selected = true
        self.selectButton = button
    }
}
    /**
    自定义Button的点击事件

    :param: button
    */
    func onClick(button: UIButton) {
        // 将上个选中按钮设置为未选中
        self.selectButton.selected = false
        // 当前按钮设置为选中
        button.selected = true
        // 记录选中按钮
        self.selectButton = button

        // 通过UITabBarController的selectedIndex属性设置选中了哪个UIViewController
        self.selectedIndex = button.tag
    }

// 用来记录当前选中按钮
private var currentSelectedButton = UIButton()
// 用来指示选中的背景
private var selectionIndicatorImageView: UIImageView!
// 单个item的宽度
private var itemWidth: CGFloat!
在viewDidLoad()方法中加入以下代码：

override func viewDidLoad() {
    super.viewDidLoad()

    // 记录TabBarController自带TabBar的位置
    let rect = self.tabBar.frame
    // 移除TabBarController自带的TabBar
    self.tabBar.removeFromSuperview()

    // 自定义TabBar的背景
    let backgroundView = UIView(frame: rect)
    backgroundView.backgroundColor = UIColor(patternImage: UIImage(named: "TabBarBG")!)

    self.view.addSubview(backgroundView)

    itemWidth = backgroundView.frame.size.width / CGFloat(self.viewControllers!.count)

    selectionIndicatorImageView = UIImageView(frame: CGRectMake(0, 0, itemWidth, backgroundView.frame.size.height))
    selectionIndicatorImageView.image = UIImage(named: "TabBarBGSel")

    backgroundView.addSubview(selectionIndicatorImageView)

    for var i = 0; i < viewControllers!.count; i++ {

        let button = CGMTabBarButton(frame: CGRectMake(itemWidth * CGFloat(i), 0, itemWidth, backgroundView.frame.size.height))

        let image = UIImage(named: "TabBar\(i)")!
        let selImage = UIImage(named: "TabBar\(i)Sel")!

        button.setImage(image, forState: UIControlState.Normal)
        button.setImage(selImage, forState: UIControlState.Selected)

        button.addTarget(self, action: "onClick:", forControlEvents: UIControlEvents.TouchUpInside)

        button.tag = i

        // 去掉buttond的高光效果
        button.adjustsImageWhenHighlighted = false

        backgroundView.addSubview(button)
    }             
}

func onClick(button: UIButton) {
    // 将上个选中俺就设置为为选中
    self.currentSelectedButton.selected = false
    // 当前按钮设置为选中
    button.selected = true

    self.currentSelectedButton = button

    let x = CGFloat(button.tag) + 0.5

    // 为TabBarItem的背景添加动画
    UIView.animateWithDuration(0.4, delay: 0.0, usingSpringWithDamping: 0.7, initialSpringVelocity: 10.0, options: UIViewAnimationOptions.CurveEaseInOut, animations: { () -> Void in

        self.selectionIndicatorImageView.center.x = self.itemWidth * x

        }, completion: nil)

    self.selectedIndex = button.tag
}