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本帖最后由 漆雕古代 于 2017-3-12 20:48 编辑
最近在看一点swift遇到一个问题，不知道该怎么解决，代码如下
class NamedShape {
var numberOfSides: Int = 0
var name: String
init(name: String) {
self.name = name
}
func simpleDescription() -> String {
return "A shape with \(numberOfSides) sides."
}
}
class Square: NamedShape {
var sideLength: Double
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 4
}
func area() -> Double {
return sideLength * sideLength
}
override func simpleDescription() -> String {
return "A square with sides of length \(sideLength)."
}
}
class EquilateralTriangle: NamedShape {
var sideLength: Double = 0.0
init(sideLength: Double, name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 3
}
var perimeter: Double {
get {
return 3.0 * sideLength
}
set {
self.sideLength = newValue / 3.0
}
}
override func simpleDescription() -> String {
return "An equilateral triagle with sides of length \(sideLength)."
}
}
class TriangleAndSquare {
var triangle: EquilateralTriangle {
willSet {
square.sideLength = newValue.sideLength
}
}
//var triangle.sideLength { // 由于用perimeter改变triangle的sideLength属性，导致重新设置的不是triangle而是triangle.sideLength
//willSet {
//print(newValue.sideLength)
//square.sideLength = newValue
//}
//didSet {
//print("triangle a change")
//}
//}
var square: Square {
willSet {
print(newValue.sideLength)
triangle.sideLength = newValue.sideLength
}
}
init(size: Double, name: String) {
self.square = Square(sideLength: size, name: name)
self.triangle = EquilateralTriangle(sideLength: size, name: name)
}
}
//第一次test
var triangleAndSquare = TriangleAndSquare(size: 10, name: "another test shape")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
//第二次test
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
//第三次test测试setter设置的值会不会影响willSet
triangleAndSquare.triangle.perimeter = 60
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
输出如下//第一次test输出结果
10.0
10.0
//第二次test输出结果
50.0
50.0
50.0
//第三次test输出结果
50.0
20.0
这段代码出自苹果的官方教程，目的在于让等边三角形和正方形的边长随时保持相等。
本来是一切ok的，但是我想在EquilateralTriangle中有一个perimeter属性拥有getter和setter的功能，可以直接更改sideLength的值，所以在这种情况下willSet不会触发，代码的目是无法达成的吧。
然后一试果然如此，自己尝试解决了一下，但是依旧不行，我自己思考出来的代码无法运行，上网搜索资料页偏少。
我就是想知道有没有可以解决这个问题的办法？ | 
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狗仔卡
发表于 2017-3-12 20:45:43
置顶卡
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显身卡
发表于 2017-9-18 21:54:05
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