Swift学习——A Swift Tour 对象和类

标签：swift   swift基础   实例   对象   类   

Objects and Classes  对象和类

使用关键字 class 定义一个类，在定义类的属性的时候与常量或者变量的定义相同（继承父类的属性定义不同），方法和函数的定义也相同

class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

class NamedShape {
    var numberOfSides: Int = 0
    var name: String
    
    init(name: String) {
        self.name = name
    }
    
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

使用 deinit 在对象被销毁之前做一些清理操作，同OC中的 dealloc 函数

类的继承

使用冒号 ： 进行继承，任何类不需要继承标准根类，如NSObject，可以根据需要包含或者省略一个超类

使用 override 关键字对父类的方法进行重写，如果不写关键字，编译器会报错，编译器还会自动检测写了 关键字但是父类实际上没有的方法

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)."
    }
}
let test = Square(sideLength: 5.2, name: "my test square")
test.area()
test.simpleDescription()

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 {
        sideLength = newValue / 3.0
    }
    }
    
    override func simpleDescription() -> String {
        return "An equilateral triagle with sides of length \(sideLength)."
    }
}
var triangle = EquilateralTriangle(sideLength: 3.1, name: "a triangle")
triangle.perimeter
triangle.perimeter = 9.9
triangle.sideLength

上面的构造器中进行以下三个步骤:

1. 为子类的属性赋值

2. 调用父类的构造器

3. 修改父类中定义的属性的值

使用WillSet 和 DidSet 在 setter 一个 newValue 之前和之后执行

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")
triangleAndSquare.square.sideLength
triangleAndSquare.triangle.sideLength
triangleAndSquare.square = Square(sideLength: 50, name: "larger square")
triangleAndSquare.triangle.sideLength

函数的参数只能在函数的内部使用，但是方法的参数名称除了在内部使用还可以在外部使用（第一个参数除外）

class Counter {
    var count: Int = 0
    func incrementBy(amount: Int, numberOfTimes times: Int) {
        count += amount * times
    }
}
var counter = Counter()
counter.incrementBy(2, numberOfTimes: 7)

？的另外一种用途

如果实例的值为 nil ，那么所有调用这个实例的语句都不会起作用

let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square")
let sideLength = optionalSquare?.sideLength

下一节说枚举和结构

Swift学习——A Swift Tour 对象和类,布布扣,bubuko.com

Swift学习——A Swift Tour 对象和类

标签：swift   swift基础   实例   对象   类   

原文地址：http://blog.csdn.net/zhenyu5211314/article/details/28401759