Swift-属性监听

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)