Protocols，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)

swift中的协议就像Java中的接口一样？     任何人都可以解释一下上面例子中willSet和didSet到底是做什么的吗？

Answer 1

1。财产观察员

• 当属性的值即将发生变化时，willSet中的代码会被调用。
• 另一方面，当刚刚更改了属性的值时，将调用didSet。

2。协议

如果协议对您有帮助，您可以将协议视为接口，但您可能希望watch the WWDC video "Protocol-oriented programming"查看协议在实践中的使用方式。