Swift中的willSet与didSet zhuan

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)") 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 
*/

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