Swift-类

1. 类的初探

class Person {
    
    let firstName: String
    let lastName: String
    var career: String?
    
    init(firstName: String, lastName: String, career: String) {
        self.firstName = firstName
        self.lastName = lastName
        self.career = career
    }
    
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
    
    func fullName() -> String {
        return firstName + " " + lastName
    }
}

let person = Person(firstName: "qin", lastName: "zhen", career: "programmer")
person.fullName()

2. 添加一个新的方法（方法可以改变对象的值）

func setNewCareer(newCareer: String) {
        self.career = newCareer
    }
//对于引用类型而言，变量的实例是一个常量的话，依然可以修改定义在类中可变量的值，且可以通过方法直接修改实例本身
person.setNewCareer(newCareer: "freelancer") //不报错

3. 引用类型对比值类型

// 方法前不加mutating关键字会报错
//类比结构体
struct Location {
    var x: Int = 0
    var y: Int = 0
    
    mutating func goEast(){
        self.x += 1 //如果不加mutating则报错，x不可修改
    }
}
var location = Location()
location.goEast()

//类比枚举
enum Switch {
    case On
    case Off
    
    mutating func click() {
        switch self {
        case .On:
            self = .Off
        case .Off:
            self = .On
        }
    }
}
var button = Switch.Off
button.click()

4. 引用类型的比较

let person1 = Person(firstName: "qin", lastName: "zhen", career: "programmer")
let person2 = person

//person2 == person1 //报错
person2 === person1 //true，判断两个对象是否指向同一块内存空间，符号适用于引用类型

let person3 = Person(firstName: "qin", lastName: "zhen", career: "programmer")

person3 === person1 //false，person1和person3分别指向两块不同的内存空间
person3 !== person1 //true

。

5. 什么时候用结构体，什么时候用类

1. 把结构看作是值：位置（经纬度），坐标（二维、三维坐标），温度等（栈）
2. 把类看作是物体：人、车、商品、动物等 （堆）

6. 计算型属性

struct Point {
    
    var x = 0.0
    var y = 0.0
}

struct Size {
    
    var width = 0.0
    var height = 0.0
}

class Rectangle {
    
    var origin = Point()
    var size = Size()

    //计算型属性必须声明为var
    var center: Point {
        
        // getter和setter方法
        get {
            let centerX = origin.x + size.width / 2
            let centerY = origin.y + size.height / 2
            return Point(x: centerX, y: centerY)
        }
        
        set {
            origin.x = newValue.x - size.width / 2
            origin.y = newValue.y - size.height / 2
        }
    }
    
    init(origin: Point, size: Size) {
        self.origin = origin
        self.size = size
    }
    
    //如果只是取值，直接return即可
    var area: Double {
        return size.height * size.width
    }
}

var rec = Rectangle(origin: Point(), size: Size(width: 10, height: 10))

//使用get方法获取属性值
rec.center
//使用set方法修改center坐标
rec.center = Point()