Question

这是来自Apple的Doc：

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)
    }
}

如果我关注Doc，

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

但如果我只是更改triangle.sideLength：

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

但square.sideLength不是willSet ed：

triangleAndSquare.square.sideLength //50.0

似乎willSet需要绑定到triangle或square，因为square.sideLength = newValue.sideLength

如果我设置了triangle的属性，但是没有创建新的square对象，我怎样才能直接更改Square的属性？

Answer 1

它没有像您期望的那样工作，因为willSet＆amp;合。对实际财产（在这种情况下为triangle＆amp; square）进行更改。由于它们是类，修改它们的属性不会改变表示它们的类指针，只会改变它的内容依次指向它（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，你必须继承类Square＆amp; Triangle在您要观察的属性上为这些子类提供willSet。为了使它按预期工作，每个子类都必须有一个新属性（比如brother: NameShape），你必须在复合类的init中设置它们，这样它们就可以互相改变了属性。

Swift：如何直接设置对象的属性？

1 个答案: