swift語言的學習筆記十一(willSet與didSet)

標籤：swift   willset   didset   

在Swift語言中用了willSet和didSet這兩個特性來監視屬性的除初始化之外的屬性值變化

無需說太多，看看下面的代碼你就能很快明白的

複製代碼
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屬性變化前做點什麼    willSet    {        println("Will set an new value \(newValue) to age")    }    //我們需要在age屬性發生變化後，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())

/*程式輸出
Will set an new value 20 to age
age filed changed form 0 to 20
Full Name: Big Zhang San , Age: 20
*/

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swift語言的學習筆記十一(willSet與didSet)