斯威夫特：如何直接設置對象的屬性？

Question

這是Apple Doc的代碼：

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)
    }
}

如果我遵循文檔，

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

但是如果我只是更改triangle.sideLength ：

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

但是square.sideLength不是willSet ed：

triangleAndSquare.square.sideLength //50.0 

似乎willSet需要綁定到triangle或square ，因為square.sideLength = newValue.sideLength

僅在設置square的屬性而不創建新的Square對象時，如何直接更改triangle的屬性？

Answer 1

它無法正常工作，因為willSet ＆co。 作用於實際屬性（在本例中為triangle和square ）的變化。 由於它們是類，因此修改其屬性不會更改表示它們的類指針，而只會更改其內容所指向的位置（即，它是相同的三角形和正方形，而不是新實例）。

要執行您想要的操作，您將必須對Square和Triangle類進行子類化，以在您要觀察的屬性的這些子類中提供willSet 。 為了使其按預期工作，每個子類都必須具有一個新屬性（例如brother: NameShape ），您必須在復合類的init進行設置，以便它們可以更改彼此的屬性。