实现控件的缩放很简单，就是用动画改变frame的大小。
func animateLabel() {
// 1
holderView.removeFromSuperview()
view.backgroundColor = Colors.blue
// 2
var label: UILabel = UILabel(frame: view.frame)
label.textColor = Colors.white
label.font = UIFont(name: "HelveticaNeue-Thin", size: 170.0)
label.textAlignment = NSTextAlignment.Center
label.text = "S" label.transform = CGAffineTransformScale(label.transform, 0.25, 0.25)
view.addSubview(label)
// 3
UIView.animateWithDuration(0.4, delay: 0.0, usingSpringWithDamping: 0.7, initialSpringVelocity: 0.1, options: UIViewAnimationOptions.CurveEaseInOut,
animations: ({
label.transform = CGAffineTransformScale(label.transform, 4.0, 4.0) }), completion: nil)}
和操作layer的动画不同，控件缩放其实是调用UIView的静态方法。设置缩放比例即可。
