如何在Swift中覆盖setter

Question

超类:

class MySuperView : UIView{
    var aProperty ;
}

子类继承超类:

class Subclass : MySuperClass{
    // I want to override the aProperty's setter/getter method
}

我想覆盖超类的属性的setter/getter方法,

如何在Swift中覆盖此方法？请帮帮我,谢谢.

Answer 1

你想用自定义setter做什么？如果您希望类在设置值之前/之后执行某些操作,则可以使用willSet/ didSet:

class TheSuperClass { 
   var aVar = 0 
} 

class SubClass: TheSuperClass { 
     override var aVar: Int { 
         willSet { 
            print("WillSet aVar to \(newValue) from \(aVar)") 
        } 
        didSet { 
            print("didSet aVar to \(aVar) from \(oldValue)") 
        } 
    } 
} 


let aSub = SubClass()
aSub.aVar = 5

控制台输出:

将aVar从0设置为5

did将aVar从0设置为5

但是,如果要完全更改setter与超类的交互方式:

class SecondSubClass: TheSuperClass { 
     override var aVar: Int { 
        get {
            return super.aVar
        }
        set { 
            print("Would have set aVar to \(newValue) from \(aVar)") 
        } 
    } 
} 

let secondSub = SecondSubClass()
print(secondSub.aVar)
secondSub.aVar = 5
print(secondSub.aVar)

控制台输出:

0

将aVar从0设置为5

0