dotOne.transform = CGAffineTransform.init(scaleX: 0.01, y: 0.01)
// OptionSet，可以多选，例如[.repeat, .autoreverse]
UIView.animate(withDuration: 0.6, delay: 0.0, options: [.repeat, .autoreverse], animations: {
self.dotOne.transform = CGAffineTransform.identity
}, completion: nil)
// 枚举写发，不同于oc
enum vcName: String {
case chat = "ChatViewController"
case stories = "StoriesViewController"
case discover = "DiscoverViewController"
}
// rawvalue
let chatVC = UIViewController.init(nibName: vcName.chat.rawValue, bundle: nil)
// didMove，少了这行代码，view是乱的
childVC.didMove(toParentViewController: parentViewController)