转载请注明出处：http://www.jianshu.com/p/d487a87105e7 ，本文出自老初的简书.

如何自定义TabBarController我们在上一篇已经讲过，现在为自定义的TabBar增加动画效果。

直接上代码：

// 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)
    }              
}

添加onClick方法，动画效果也在这里面实现：

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
}

最终效果如下：

效果展示.gif

GIF截的不好，各位老师都是用的什么截图软件啊？

GitHub地址