Swift 4.2基础---继承

继承（Inheritance）

1.基类

• 基类是不继承其他任何类的类；

class Vehicle {
    var currentSpeed = 0.0
    var description: String {
        return "traveling at \(currentSpeed) miles per hour"
    }
    func makeNoise() {
        // do nothing - an arbitrary vehicle doesn't necessarily make a noise
    }
}

2.子类

子类化语法格式：

class SomeSubclass: SomeSuperclass {
    // subclass definition goes here
}

class Bicycle: Vehicle {
    var hasBasket = false
}

class Tandem: Bicycle {
    var currentNumberOfPassengers = 0
}

3.重写

在Swift中，使用关键字override表明在子类中重写了父类的方法，属性或下标。

(1).访问父类的方法，属性，下标

• 当在子类中需要访问父类的方法，属性，下标时，用关键字super来访问。

(2).重写方法

class Train: Vehicle {
    override func makeNoise() {
        print("Choo Choo")
    }
}

let train = Train()
train.makeNoise()

(3)重写属性的Getters 和 Setters方法

class Car: Vehicle {
    var gear = 1
    override var description: String {
        return super.description + " in gear \(gear)"
    }
}

let car = Car()
car.currentSpeed = 25.0
car.gear = 3
print("Car: \(car.description)")
// Car: traveling at 25.0 miles per hour in gear 3

(4).重写属性的监听者

class AutomaticCar: Car {
    override var currentSpeed: Double {
        didSet {
            gear = Int(currentSpeed / 10.0) + 1
        }
    }
}

let automatic = AutomaticCar()
automatic.currentSpeed = 35.0
print("AutomaticCar: \(automatic.description)")
// AutomaticCar: traveling at 35.0 miles per hour in gear 4

3.防止重写

将父类的方法，属性，下标标记为final来防止被子类重写。

4.其他专题模块

Swift 4.2 基础专题详解