swift 學習筆記(23)-屬性(計算屬性)

計算屬性,前面已經提到過一些.大緻和 oc 中的 set 和get 方法差不多,讀取和指派等

//點

struct Point{
    var x = 100
    var y = 100
}
var point = Point()
print(point)


// 寬高
struct Size{
    var width = 100
    var height = 100
}
var size = Size()
print(size)

//區域
struct Rect{
    var size = Size()
    var origin = Point()

    var center:Point{

        // 隻寫 get 方法,就會是隻讀屬性
        get {
            let x = rect.origin.x + rect.size.width/2
            let y = rect.origin.y + rect.size.height/2
            return Point(x: x , y: y )
        }
        //set 隻是通過一種途徑來修改屬性的值
        set(newValue) {

            let x = newValue.x - size.width/2
            let y = newValue.y - size.height/2
            origin = Point(x: x, y:y)


        }
    }



}
var rect = Rect()
print(rect)



//求區域中心點



var p = Point(x: 100, y: 100)
var s = Size(width: 100, height: 100)
var r = Rect(size: s, origin: p)
print(r.center)
r.center = Point(x: 10, y: 10)
print(r.origin)