class Dog: NSObject {

    var name:String?{

//        属性监听器

//        属性即将改变监听

        willSet{

//            print("111")

//            print(name)

            print(newValue)

        }

//        属性已经改变监听

//        开发中常用这个监听属性改变

        didSet{

//            print("222")

//            print(name)

            print(oldValue)

        }

    }

}

let d = Dog()

d.name = "why"

//d.name = "ee"

print(d.name)