willSet and didSet observers are not called when a property is first initialized. They are only called when the property’s value is set outside of an initialization context.
英語不好环肘，翻譯的大概意思就是willSet和didSet如果在初始化的時(shí)候調(diào)用是無效的
但是又非常想在初始化的時(shí)候調(diào)用didSet柬批，那么可以采用KVC的方式給對(duì)象初始化搏嗡，就可以調(diào)用didSet了
