swift - 快速覆盖实例属性(帮助)

Question

嗨，我最近开始学习 swift ，在阅读继承章节时，我遇到了这个问题，所以我创建了一个车辆类作为我的父类(super class)，创建了一个汽车类作为我的子类，汽车类继承自车辆类，之后我创建了一个automaticCar类作为另一个子类，它继承自car类(如果有任何歧义，请查看代码)，所以当我尝试覆盖dangerText时，Xcode似乎跳过了代码并且不会更改dangerText:- (如果我做错了什么，请告诉我，我不是在寻找替代方法，因此请通过使用覆盖解决方案更正我的代码来回答提前致谢!

import Foundation
class viehcle {
//SuperClass viehcle
var currentSpeed = 0
let maxSpeed = 180
var descripion:String{
    return "Current speed is \(currentSpeed)"
 }
}
class car:viehcle{
//SubClass car inherits from viehcle
var currentGear = 1
var dangerText = ""
//override of description instance property
override var descripion: String{
    return ("The current speed is \(super.currentSpeed) and the gear is \(currentGear) \(dangerText)")
 }
}
class AutomaticCar:car{
//SubClass AutomaticCar which inherits fom superClass car 


//override of dangerText instance property of car
override var dangerText: String{
    didSet{
        if currentSpeed>maxSpeed{
            let slowDown = "Slow Down !"
            dangerText = dangerText.stringByAppendingString(slowDown)
        }
    }
}
//override current speed instance property of car
override var currentSpeed: Int{
    didSet{

        currentGear = (currentSpeed/40)+1

        if currentGear <= 4 {

        currentGear = self.currentGear

        }
        else{
            currentGear = 4
           }
       }
  }
}

var myCar = car() // obj/instance created from car class
var myAutomaticCar = AutomaticCar() // obj/instance created from AutomaticCar class
myAutomaticCar.currentSpeed = 300 // set Automatic car's current speed to 300

print(myCar.descripion)
print(myAutomaticCar.descripion)

Answer 1

您在 AutomaticCar 类(class)中犯了一个小错误。在该类中，无需覆盖dangerText，而是当您将新值设置为currentSpeed时，只需更新dangerText，如下所示...

class AutomaticCar:car {
    override var currentSpeed: Int {
        didSet {
            currentGear = (currentSpeed/40)+1
            if currentGear <= 4 {
                currentGear = self.currentGear
            }
            else{
                currentGear = 4
            }
            if currentSpeed > maxSpeed {
                let slowDown = "Slow Down !"
                dangerText = dangerText.stringByAppendingString(slowDown)
            }
        }
    }
}

现在检查dangerText将附带给定当前速度和最大速度的描述。