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 */