Swift中的willSet与didSet zhuan

import Foundationclass People : NSObject
{//普通属性var firstName:String = ""var lastName:String  = ""var nickName:String  = ""//计算属性
    var fullName:String{get{return nickName + " " + firstName + " " + lastName}}//带属性监视器的普通属性var age:Int = 0{//我们需要在age属性变化前做点什么
        willSet{println("Will set an new value \(newValue) to age")}//我们需要在age属性发生变化后，更新一下nickName这个属性
        didSet{println("age filed changed form \(oldValue) to \(age)")if age<10{nickName = "Little"}else{nickName = "Big"}}}func toString() -> String{return "Full Name: \(fullName) " + ", Age: \(age) "}}var me = People()
me.firstName = "Zhang"
me.lastName  = "San"
me.age = 20println(me.toString())/*程序输出
Will set an new value 20 to age
age filed changed form 0 to 20
Full Name: Big Zhang San , Age: 20
*/