在Swift語言中用了willSet和didSet這兩個特性來監(jiān)視屬性的除初始化之外的屬性值變化
無需說太多吠裆，看看下面的代碼你就能很快明白的
import Foundation
class People : NSObject
{
//普通屬性
var firstName:String = ""
var lastName:String = ""
var nickName:String = ""
//計算屬性
var fullName:String
{
get
{
return nickName + " " + firstName + " " + lastName
}
}
//帶屬性監(jiān)視器的普通屬性
var age:Int = 0
{
//我們需要在age屬性變化前做點什么
willSet
{
println("Will set an new value \(newValue) to age")
}
//我們需要在age屬性發(fā)生變化后父阻，更新一下nickName這個屬性
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())
/*程序輸出
Will set an new value 20 to age
age filed changed form 0 to 20
Full Name: Big Zhang San , Age: 20
*/
