Swift中的willSet与didSet

Swift中的willSet与didSet

周银辉

在Swift语言中用了willSet和didSet这两个特性来监视属性的除初始化之外的属性值变化

无需说太多，看看下面的代码你就能很快明白的

import Foundation

class 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)")ifage<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*/