苹果编程语言Swift中文教程.doc

《苹果编程语言Swift中文教程.doc》由会员分享，可在线阅读，更多相关《苹果编程语言Swift中文教程.doc（13页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、苹果编程语言Swift中文教程：Swift简介本文来自于：这篇文章简要介绍了苹果于WWDC 2014发布的编程语言Swift。Swift是什么？Swift是苹果于WWDC 2014发布的编程语言，这里引用The Swift Programming Language的原话：“”Swift is a new programming language for iOS and OS X apps that builds on the best of C and Objective-C, without the constraints of C compatibility.Swift adopts sa

2、fe programming patterns and adds modern features to make programming easier, more flexible and more fun.Swifts clean slate, backed by the mature and much-loved Cocoa and Cocoa Touch frameworks, is an opportunity to imagine how software development works.Swift is the first industrial-quality systems

3、programming language that is as expressive and enjoyable as a scripting language.简单的说：“”Swift用来写iOS和OS X程序。（估计也不会支持其它屌丝系统）Swift吸取了C和Objective-C的优点，且更加强大易用。Swift可以使用现有的Cocoa和Cocoa Touch框架。Swift兼具编译语言的高性能（Performance）和脚本语言的交互性（Interactive）。Swift语言概览基本概念注：这一节的代码源自The Swift Programming Language中的A Swift

4、 Tour。Hello, world类似于脚本语言，下面的代码即是一个完整的Swift程序。“”println(Hello, world) 变量与常量Swift使用var声明变量，let声明常量。“”var myVariable = 42myVariable = 50let myConstant = 42类型推导Swift支持类型推导（Type Inference），所以上面的代码不需指定类型，如果需要指定类型：“”let explicitDouble : Double = 70Swift不支持隐式类型转换（Implicitly casting），所以下面的代码需要显式类型转换（Explici

5、tly casting）：“”let label = The width is let width = 94let width = label + String(width)字符串格式化Swift使用(item)的形式进行字符串格式化：“”let apples = 3let oranges = 5let appleSummary = I have (apples) apples.let appleSummary = I have (apples + oranges) pieces of fruit.数组和字典Swift使用操作符声明数组（array）和字典（dictionary）：“”var

6、shoppingList = catfish, water, tulips, blue paintshoppingList1 = bottle of watervar occupations = Malcolm: Captain, Kaylee: Mechanic,occupationsJayne = Public Relations一般使用初始化器（initializer）语法创建空数组和空字典：“” let emptyArray = String() let emptyDictionary = Dictionary()如果类型信息已知，则可以使用声明空数组，使用:声明空字典。控制流概览Sw

7、ift的条件语句包含if和switch，循环语句包含for-in、for、while和do-while，循环/判断条件不需要括号，但循环/判断体（body）必需括号：“”let individualScores = 75, 43, 103, 87, 12var teamScore = 0for score in individualScores if score 50 teamScore += 3 else teamScore += 1 可空类型结合if和let，可以方便的处理可空变量（nullable variable）。对于空值，需要在类型声明后添加?显式标明该类型可空。“”var opt

8、ionalString: String? = HellooptionalString = nilvar optionalName: String? = John Appleseedvar gretting = Hello!if let name = optionalName gretting = Hello, (name)灵活的switchSwift中的switch支持各种各样的比较操作：“”let vegetable = red pepperswitch vegetable case celery: let vegetableComment = Add some raisins and ma

9、ke ants on a log.case cucumber, watercress: let vegetableComment = That would make a good tea sandwich.case let x where x.hasSuffix(pepper): let vegetableComment = Is it a spicy (x)?default: let vegetableComment = Everything tastes good in soup.其它循环for-in除了遍历数组也可以用来遍历字典：“”let interestingNumbers = Pr

10、ime: 2, 3, 5, 7, 11, 13, Fibonacci: 1, 1, 2, 3, 5, 8, Square: 1, 4, 9, 16, 25,var largest = 0for (kind, numbers) in interestingNumbers for number in numbers if number largest largest = number largestwhile循环和do-while循环：“”var n = 2while n 100 n = n * 2nvar m = 2do m = m * 2 while m 100mSwift支持传统的for循环

11、，此外也可以通过结合.（生成一个区间）和for-in实现同样的逻辑。“”var firstForLoop = 0for i in 0.3 firstForLoop += ifirstForLoopvar secondForLoop = 0for var i = 0; i String return Hello (name), today is (day).greet(Bob, Tuesday)通过元组（Tuple）返回多个值：“”func getGasPrices() - (Double, Double, Double) return (3.59, 3.69, 3.79)getGasPrice

12、s()支持带有变长参数的函数：“”func sumOf(numbers: Int.) - Int var sum = 0 for number in numbers sum += number return sumsumOf()sumOf(42, 597, 12)函数也可以嵌套函数：“”func returnFifteen() - Int var y = 10 func add() y += 5 add() return yreturnFifteen()作为头等对象，函数既可以作为返回值，也可以作为参数传递：“”func makeIncrementer() - (Int - Int) func

13、 addOne(number: Int) - Int return 1 + number return addOnevar increment = makeIncrementer()increment(7) func hasAnyMatches(list: Int, condition: Int - Bool) - Bool for item in list if condition(item) return true return falsefunc lessThanTen(number: Int) - Bool return number Int in let result = 3 * n

14、umber return result )当闭包的类型已知时，可以使用下面的简化写法：“”numbers.map( number in 3 * number )此外还可以通过参数的位置来使用参数，当函数最后一个参数是闭包时，可以使用下面的语法：“”sort(1, 5, 3, 12, 2) $0 $1 类和对象 创建和使用类Swift使用class创建一个类，类可以包含字段和方法：“”class Shape var numberOfSides = 0func simpleDescription() - String return A shape with (numberOfSides) side

15、s.创建Shape类的实例，并调用其字段和方法。“”var shape = Shape()shape.numberOfSides = 7varshapeDescription = shape.simpleDescription()通过init构建对象，既可以使用self显式引用成员字段（name），也可以隐式引用（numberOfSides）。“”class NamedShape var numberOfSides: Int = 0 var name: String init(name: String) self.name = name func simpleDescription() - S

16、tring return A shape with (numberOfSides) sides. 使用deinit进行清理工作。继承和多态Swift支持继承和多态（override父类方法）：“”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 * side

17、Length 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()注意：如果这里的simpleDescription方法没有被标识为override，则会引发编译错误。属性为了简化代码，Swift引入了属性（property），见下面的perimeter字段：“”class Equ

18、ilateralTriangle: 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 A

19、n equilateral triagle with sides of length (sideLength). var triangle = EquilateralTriangle(sideLength: 3.1, name: a triangle)triangle.perimetertriangle.perimeter = 9.9triangle.sideLength注意：赋值器（setter）中，接收的值被自动命名为newValue。willSet和didSetEquilateralTriangle的构造器进行了如下操作：为子类型的属性赋值。 调用父类型的构造器。 修改父类型的属性。如果

20、不需要计算属性的值，但需要在赋值前后进行一些操作的话，使用willSet和didSet：“”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)

21、triangle = EquilateralTriangle(sideLength: size, name: name) var triangleAndSquare = TriangleAndSquare(size: 10, name: another test shape)triangleAndSquare.square.sideLengthtriangleAndSquare.square = Square(sideLength: 50, name: larger square)triangleAndSquare.triangle.sideLength从而保证triangle和square拥

22、有相等的sideLength。调用方法Swift中，函数的参数名称只能在函数内部使用，但方法的参数名称除了在内部使用外还可以在外部使用（第一个参数除外），例如：“”class Counter var count: Int = 0 func incrementBy(amount: Int, numberOfTimes times: Int) count += amount * times var counter = Counter()counter.incrementBy(2, numberOfTimes: 7)注意Swift支持为方法参数取别名：在上面的代码里，numberOfTimes面向外

23、部，times面向内部。?的另一种用途使用可空值时，?可以出现在方法、属性或下标前面。如果?前的值为nil，那么?后面的表达式会被忽略，而原表达式直接返回nil，例如：“”let optionalSquare: Square? = Square(sideLength: 2.5, name: optionalsquare)let sideLength = optionalSquare?.sideLength当optionalSquare为nil时，sideLength属性调用会被忽略。枚举和结构枚举使用enum创建枚举注意Swift的枚举可以关联方法：“”enum Rank: Int case

24、Ace = 1 case Two, Three, Four, Five, Six, Seven, Eight, Nine, Ten case Jack, Queen, King func simpleDescription() - String switch self case .Ace: return ace case .Jack: return jack case .Queen: return queen case .King: return king default: return String(self.toRaw() let ace = Rank.Acelet aceRawValue

25、 = ace.toRaw()使用toRaw和fromRaw在原始（raw）数值和枚举值之间进行转换：“”if let convertedRank = Rank.fromRaw(3) let threeDescription = convertedRank.simpleDescription()注意枚举中的成员值（member value）是实际的值（actual value），和原始值（raw value）没有必然关联。一些情况下枚举不存在有意义的原始值，这时可以直接忽略原始值：“”enum Suit case Spades, Hearts, Diamonds, Clubs func simp

26、leDescription() - String switch self case .Spades: return spades case .Hearts: return hearts case .Diamonds: return diamonds case .Clubs: return clubs let hearts = Suit.Heartslet heartsDescription = hearts.simpleDescription()除了可以关联方法，枚举还支持在其成员上关联值，同一枚举的不同成员可以有不同的关联的值：“”enum ServerResponse case Resul

27、t(String, String) case Error(String)let success = ServerResponse.Result(6:00 am, 8:09 pm)let failure = ServerResponse.Error(Out of cheese.)switch success case let .Result(sunrise, sunset): let serverResponse = Sunrise is at (sunrise) and sunset is at (sunset). case let .Error(error): let serverRespo

28、nse = Failure. (error)结构Swift使用struct关键字创建结构。结构支持构造器和方法这些类的特性。结构和类的最大区别在于：结构的实例按值传递（passed by value），而类的实例按引用传递（passed by reference）。“”struct Card var rank: Rank var suit: Suit func simpleDescription() - String return The (rank.simpleDescription() of (suit.simpleDescription() let threeOfSpades = Car

29、d(rank: .Three, suit: .Spades)let threeOfSpadesDescription = threeOfSpades.simpleDescription()协议（protocol）和扩展（extension） 协议Swift使用protocol定义协议：“”protocol ExampleProtocol var simpleDescription: String get mutating func adjust()类型、枚举和结构都可以实现（adopt）协议：“”class SimpleClass: ExampleProtocol var simpleDesc

30、ription: String = A very simple class. var anotherProperty: Int = 69105 func adjust() simpleDescription += Now 100% adjusted. var a = SimpleClass()a.adjust()let aDescription = a.simpleDescriptionstruct SimpleStructure: ExampleProtocol var simpleDescription: String = A simple structure mutating func

31、adjust() simpleDescription += (adjusted) var b = SimpleStructure()b.adjust()let bDescription = b.simpleDescription扩展扩展用于在已有的类型上增加新的功能（比如新的方法或属性），Swift使用extension声明扩展：“”extension Int: ExampleProtocol var simpleDescription: String return The number (self) mutating func adjust() self += 42 7. simpleDes

32、cription泛型（generics）Swift使用来声明泛型函数或泛型类型：“”func repeat(item: ItemType, times: Int) - ItemType var result = ItemType() for i in 0.times result += item return resultrepeat(knock, 4)Swift也支持在类、枚举和结构中使用泛型：“”/ Reimplement the Swift standard librarys optional typeenum OptionalValue case None case Some(T)va

33、r possibleInteger: OptionalValue= .NonepossibleInteger = .Some(100)有时需要对泛型做一些需求（requirements），比如需求某个泛型类型实现某个接口或继承自某个特定类型、两个泛型类型属于同一个类型等等，Swift通过where描述这些需求：“”func anyCommonElements (lhs: T, rhs: U) - Bool for lhsItem in lhs for rhsItem in rhs if lhsItem = rhsItem return true return falseanyCommonElements(1, 2, 3, 3)Swift语言概览就到这里，有兴趣的朋友请进一步阅读The Swift Programming Language。