https://newgr8player.com/2018/03/24/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F-%E8%A7%82%E5%AF%9F%E8%80%85%E6%A8%A1%E5%BC%8F/ 设计模式-观察者模式
https://newgr8player.com/2018/03/24/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F-%E8%A7%82%E5%AF%9F%E8%80%85%E6%A8%A1%E5%BC%8F/
设计模式-观察者模式