协议、willSet和didSet

Question

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(sideLength: size, name: name)
        triangle = EquilateralTriangle(sideLength: size, name: name)
    }
}
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.triangle.sideLength)

斯威夫特的协议就像Java中的接口？有人能解释一下上面的例子中的willSet和didSet到底是什么吗？

Answer 1

1.财产观察员

• 当属性值即将更改时，将调用willSet中的代码。
• 另一方面，当一个属性值刚刚被更改时，didSet就会被调用。

2.议定书

如果协议对您有帮助，您可以将其看作是类似于接口的协议，但您可能希望使用观看WWDC视频“面向协议的编程”。来查看协议在实践中是如何使用的。