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swift语言学习教程 苹果swift编程语言基础教程

作者:佚名 来源:绿茶软件园 2014-06-04 10:30:50 0

  swift语言学习教程,绿茶小编胖胖带来了苹果swift编程语言基础教程,对于苹果发布的这款编程语言很多朋友可能不是很了解,没关系,下文将会详细介绍这款语言的基础代码,一起来了解吧~

 

swift语言学习教程 苹果swift编程语言基础教程1
 

  --基本概念

  注:这一节的代码源自The Swift Programming Language中的A Swift 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 = 42

  ◾myVariable = 50

  ◾let 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 = 70

  Swift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(Explicitly casting):

  ◾let label = "The width is "

  ◾let width = 94

  ◾let 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 = 3

  ◾let oranges = 5

  ◾let 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 shoppingList = ["catfish", "water", "tulips", "blue paint"]

  ◾shoppingList[1] = "bottle of water"

  ◾var occupations = [

  ◾ "Malcolm": "Captain",

  ◾ "Kaylee": "Mechanic",

  ◾]

  ◾occupations["Jayne"] = "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

  Swift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, 12]

  var teamScore = 0

  for 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 optionalString: String? = "Hello"

  optionalString == nil

  var optionalName: String? = "John Appleseed"

  var gretting = "Hello!"

  if let name = optionalName {

  gretting = "Hello, \(name)"

  }

  灵活的switch

  Swift中的switch支持各种各样的比较操作:

  ◾let vegetable = "red pepper"

  ◾switch vegetable {

  ◾case "celery":

  ◾ let vegetableComment = "Add some raisins and make 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 = [

  ◾ "Prime": [2, 3, 5, 7, 11, 13],

  ◾ "Fibonacci": [1, 1, 2, 3, 5, 8],

  ◾ "Square": [1, 4, 9, 16, 25],

  ◾]

  ◾var largest = 0

  ◾for (kind, numbers) in interestingNumbers {

  ◾ for number in numbers {

  ◾ if number > largest {

  ◾ largest = number

  ◾ }

  ◾ }

  ◾}

  ◾largest

  while循环和do-while循环:

  ◾var n = 2

  ◾while n < 100 {

  ◾ n = n * 2

  ◾}

  ◾n

  ◾var m = 2

  ◾do {

  ◾ m = m * 2

  ◾} while m < 100

  ◾m

  Swift支持传统的for循环,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 = 0

  ◾for i in 0..3 {

  ◾ firstForLoop += i

  ◾}

  ◾firstForLoop

  ◾var secondForLoop = 0

  ◾for var i = 0; i < 3; ++i {

  ◾ secondForLoop += 1

  ◾}

  注意:Swift除了..还有...:..生成前闭后开的区间,而...生成前闭后闭的区间。
 

  --函数和闭包

  函数

  Swift使用func关键字声明函数:

  ◾func greet(name: String, day: String) -> 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)

  ◾}

  ◾getGasPrices()

  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 sum

  ◾}

  ◾sumOf()

  ◾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 y

  ◾}

  ◾returnFifteen()

  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 addOne(number: Int) -> Int {

  ◾ return 1 + number

  ◾ }

  ◾ return addOne

  ◾}

  ◾var increment = makeIncrementer()

  ◾increment(7)

  ◾func hasAnyMatches(list: Int[], condition: Int -> Bool) -> Bool {

  ◾ for item in list {

  ◾ if condition(item) {

  ◾ return true

  ◾ }

  ◾ }

  ◾ return false

  ◾}

  ◾func lessThanTen(number: Int) -> Bool {

  ◾ return number < 10

  ◾}

  ◾var numbers = [20, 19, 7, 12]

  ◾hasAnyMatches(numbers, lessThanTen)

  闭包

  本质来说,函数是特殊的闭包,Swift中可以利用{}声明匿名闭包:

  ◾numbers.map({

  ◾ (number: Int) -> Int in

  ◾ let result = 3 * number

  ◾ 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 = 0

  ◾func simpleDescription() -> String {

  ◾return "A shape with \(numberOfSides) sides."

  ◾}

  ◾}

  创建Shape类的实例,并调用其字段和方法。

  ◾var shape = Shape()

  ◾shape.numberOfSides = 7

  ◾varshapeDescription = 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() -> String {

  ◾ 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 * 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()

  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。

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关键词: swift语言 swift 编程
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