ios - Swift:如何直接设置对象的属性？

Question

这是 Apple 文档中的代码:

class NameShape{
    var numberOfSide: Int = 0
    var name:String
    func simpleDescription() -> String {
        return "A square with \(numberOfSide) sides."
    }
    init (name: String){
        self.name = name
        }
}

class Square:NameShape{
    var sideLength: Double
    init(name: String, sideLength: Double){
        self.sideLength = sideLength
        super.init(name: name)


        numberOfSide = 4
    }

    func area() ->Double {
        return sideLength * sideLength
    }

    override func simpleDescription() -> String {
        return "A square with sides of length \(sideLength)."
    }

}

class EquilateralTriangle:NameShape{
    var sideLength: Double = 0.0

    init(sideLength: Double, name: String){
        self.sideLength = sideLength
        super.init(name: name)
        numberOfSide = 3
    }

    var perimeter: Double{
    get{
        return 3.0 * sideLength
    }
    set{
        sideLength = newValue / 3.0
    }
    }

    override func simpleDescription() -> String {
        return "An equilateral triangle with sides of length \(sideLength)."
    }
}

class TriangleAndSquare{
    var triangle:EquilateralTriangle{
    willSet {
    square.sideLength = newValue.sideLength
    }
    }
    var square: Square{
    willSet {
        triangle.sideLength = newValue.sideLength
    }
    }
    init(size: Double, name: String){
        square = Square(name: name, sideLength: size)
        triangle = EquilateralTriangle(sideLength: size, name: name)
    }
}

如果我遵循文档，

var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
triangleAndSquare.square.sideLength //10.0
triangleAndSquare.triangle.sideLength //10.0
triangleAndSquare.square = Square(name: "larger square", sideLength: 50)
triangleAndSquare.triangle.sideLength //500.0

但如果我只是改变triangle.sideLength:

triangleAndSquare.triangle.sideLength = 25
triangleAndSquare.triangle.sideLength //25.0

但是 square.sideLength 不是 willSeted:

triangleAndSquare.square.sideLength //50.0 

似乎 willSet 需要绑定(bind)到 triangle 或 square，因为 square.sideLength = newValue.sideLength

如果我设置了square的属性，我如何才能直接改变triangle的属性，而不是创建一个新的Square 对象？

Answer 1

它没有像您预期的那样工作，因为 willSet & co.作用于实际属性(在本例中为 triangle 和 square)变化。因为它们是类，修改它们的属性不会改变代表它们的类指针，只会改变它的内容依次指向的地方(即它是相同的三角形和正方形，而不是新实例)。

要做你想做的事，你必须子类 Square 和 Triangle 以在属性的这些子类中提供 willSet你想观察。为了使其按预期工作，每个子类都必须有一个新属性(比如 brother: NameShape )，您必须在复合类的 init 中设置该属性, 这样他们就可以改变彼此的属性。