Swift语言中用了willSet和didSet

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

import Foundation

class People : NSObject

{

//普通属性

var name1:String = ""

var lastName:String = ""

var nickName:String = ""

//计算属性

var fullName:String

{

get

{

return nickName + " " + name1 + " " + 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 = 20

println(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

*/