Swift中的willSet与didSet

<p style="margin: 10px auto; padding-top: 0px; padding-bottom: 0px; line-height: 24px; font-size: 13px; font-family: Verdana,Arial,Helvetica,sans-serif; color: rgb(51,51,51);"></p><p style="margin: 10px auto; padding-top: 0px; padding-bottom: 0px; color: rgb(51,51); font-family: Verdana,sans-serif; font-size: 13px; line-height: 24px;">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</p><p style="margin: 10px auto; padding-top: 0px; padding-bottom: 0px; color: rgb(51,sans-serif; font-size: 13px; line-height: 24px;">无需说太多，看看下面的代码你就能很快明白的</p>

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)")
            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
*/

（编辑：李大同）

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