ASwiftTour(4)-ObjectsandClasses

2019-11-14 20:25:23

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Objects and Classes(对象和类)

用 class 关键字后面跟一个类名来创建一个class，在一个类中声明常亮或变量，他存在于当前类的上下文，函数的方法是同样的

var numberOfSides = 0    let numberOfSidesLet = 1        func simpleDescription() -> String    {        return "A shape with /(numberOfSides)  /(numberOfSidesLet) sides."    }

通过括号的方式来创建一个类实例，使用点语法来访问该实例的属性和方法

var shape = Shape()shape.numberOfSides=10var str = shape.simpleDescription()PRintln(str)

吐槽一下，不知道是xcode6 bate版本问题还是什么原因，写代码的提示功能特别差

这个版本的一个重要的修改：在创建的时候设置初始值的项，使用init来创建，如下：

 1 class Shape { 2      3     var name:String 4      5     init(name:String) 6     { 7         self.name = name 8     } 9     10     var numberOfSides = 011     let numberOfSidesLet = 112     13     14     func simpleDescription() -> String15     {16         return "A shape with /(numberOfSides)  /(numberOfSidesLet) sides."17     }18 }

请注意 self 关键字用来区分属性name 和参数 name(这个和oc中的还是一样)

如果你要释放一些对象，那么需要创建一个deinitializer，使用deinit来释放资源

子类和父类之间用冒号分开，在继承标准的子类时，不需要声明，所以可以根据需要来忽略或者包括父类

子类重写父类的方法要使用overside关键字(C#,java比较相似)，如果没有重载，则会提示错误

class Square: Shape {       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)"    }} var square = Square(sideLength:10.1,name:"my test") square.area() var str = square.simpleDescription() println(str)

除了简单的属性，属性也可以有getter 和 setter方法

 1 class EquilateralTriangle: Shape { 2     3     var sideLength:Double = 0.0 4      5     init(sideLength:Double,name:String) 6     { 7         self.sideLength = sideLength 8         super.init(name:name) 9         numberOfSides=310     }11     12     var perimeter:Double13     {14         get{15             return 3.0*sideLength16         }17         set18         {19             sideLength = newValue/3.020         }21     }22     23     override func simpleDescription()->String24     {25         return "An equilateral triagle with sides of length /(sideLength)"26     }27 }28  var triangle = EquilateralTriangle(sideLength:3.1,name:"a triangle")29  println(triangle.perimeter)30  triangle.perimeter = 9.931  println(triangle.sideLength)

在perimeter的setter方法中，新值得隐式名称是newValue,你可以在setter之后提供一个名字

初始化EquilateralTriangle类有三步：

1. 设置属性的值

2. 调用父类的构造方法(init)

3. 改变父类定义的属性值，其他的方法也可以在这里设置

如果你不需要计算属性，但是在setter之前或者之后执行，可以使用willSet和didSet，例如：下面的类永远保证三角形的边长等于正方形的边长

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:"ray test shape")        println(triangleAndSquare.square.sideLength)        println(triangleAndSquare.triangle.sideLength)        triangleAndSquare.square = Square(sideLength:50,name:"larger square")        println(triangleAndSquare.triangle.sideLength)        println(triangleAndSquare.square.sideLength)//打印出来的值为：10.0，10.0，50.0，50.0

函数和方法有一个不同点，函数的参数名只能在函数中使用，but parameters names in methods are also used when you call the method (except for the first parameter). By default, a method has the same name for its parameters when you call it and within the method itself. You can specify a second name, which is used inside the method(这个不知道怎么翻译)

 1 class Counter { 2     3     var count:Int = 0 4     func incrementBy(amount:Int,numberOfTimes times:Int) 5     { 6         count += amount*times 7     } 8 } 9  var counter = Counter()10  counter.incrementBy(2,numberOfTimes:7)11

当使用可选值时，可以像方法属性一样在操作符前使用问号(?)，如果值本来就是nil，那所有在？之后的代码将会忽略，整个表达式都是nil，Otherwise, the optional value is unwrapped, and everything after the ? acts on the unwrapped value. In both cases, the value of the whole expression is an optional value.

1  let optionalSquare :Square?=Square(sideLength:2.5,name:"optional square")2  let sideLength = optionalSquare?.sideLength  //注意：等号和optionalSquare之间必须有空格，不知道编译器为什么会这样