swift - 如何覆盖 Swift 中的属性？

Question

我有这个类和一个来自 Swift 教程的子类。遗憾的是，本教程没有提及如何覆盖属性。我的第一次测试惨遭失败:

// generic shape
class Shape {
    var numberOfSides = 0
    var name: String

    init(name: String) {
        self.name = name
    }

    func simpleDescription() -> String {
        return self.name + " with \(numberOfSides) sides."
    }
}

// creating a subclass and reset the property
class Triangle: Shape {
    // this doesnt work
    override var numberOfSides = 3

    // this also doesnt work
    var numberOfSides = 3

    // and this doesnt work either
    numberOfSides = 3

    // this works
    override func simpleDescription() -> String {
        return "Triangle name: " + self.name + " number of sides: \(numberOfSides)"
    }
}

var blurgh = Triangle(name: "supertriangle")
println(blurgh.simpleDescription())

那么在子类上设置属性的正确方法是什么？

Answer 1

在您的示例中，您不想覆盖您只想更改其值的属性。最好的方法是 init 方法:

init(name: String) {
    super.init(name: name)
    numberOfSides = 3
}

要覆盖属性，您应该对其 getter 或 setter 方法进行一些更改，例如:

override var numberOfSides  {
    get {
        return super.numberOfSides
    }
    set {
        super.numberOfSides = newValue + 10
    }
}