iOS-Swift

Swift是一门新的iOS系统的开发语言，其更轻量级，类似脚本语言，支持ARC以及Playground。Playground文件可以在修改代码时，立即看到结果。

Swift相比于OC有很多优势，例如，type-safe, 会做类型检查，避免类型转换异常;引入Optional类型，不用每次都用if语句判断一个值是否为nil;引入Tuples，可以在函数中一次返回多个不同类型的值。

下面是Swift的语法介绍。

Format

Print

无需导入输入输出或者字符串库:

1	print("Hello, world!")

如果想不自动换行:

1	print("nimei", terminator:"")

Comments

// This is a comment.
/* This is also a comment
 but is written over multiple lines. */
/* This is the start of the first multiline comment.
/* This is the second, nested multiline comment. */
 This is the end of the first multiline comment. */

注意，”/*”可以嵌套。

Semicolons

一般不需要加”;”号，除非多行写成一行:

1	let cat = "🐱"; print(cat)

Simple Values

用let定义常量，而var定义变量。不用定义类型:

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var myVariable = 42
myVariable = 50
let myConstant = 42

如果需要显式定义，可以这样写:

1	let explicitDouble: Double = 70

没有隐式的类型转换，如果需要类型转换，需要显示定义:

1	let widthLabel = "The width is " + String(94)

如果是在字符串中，可以用“\“+”()”来转换：

let apples = 3
let oranges = 5
let appleSummary = "I have \(apples) apples."
let fruitSummary = "I have \(apples + oranges) pieces of fruit."

用”[]”来创建Array和Dictionary:

var shoppingList = ["catfish", "water", "tulips", "blue paint"]
shoppingList[1] = "bottle of water"
 
var occupations = [
    "Malcolm": "Captain",
    "Kaylee": "Mechanic",
]
occupations["Jayne"] = "Public Relations"

定义一个空的需要用初始化函数:

1 2	let emptyArray = [String]() let emptyDictionary = [String: Float]()

如果是已经知道类型的变量，可以直接这样写:

1 2	shoppingList = [] occupations = [:]

用”?”定义Optional类型，Optional类型可以有值，也可以为nil。用”??”可以给Optional类型赋值一个默认值:

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let nickName: String? = nil
let fullName: String = "John Appleseed"
let informalGreeting = "Hi \(nickName ?? fullName)"

Control Flow

if语句:必须是跟着Boolean类型，不能是数字，不会隐式跟0比较:

var score = 51
if score > 51 {
	score = 100
} else {
	score = 0
}

if-let语句:必须是跟着Optional类型，如果Optional类型有值，则直接赋值，进入if语句，如果没有，则进入else语句:

var optionalString: String? = "Hello"
print(optionalString == nil)
 
var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
    greeting = "Hello, \(name)"
}

switch:支持任意格式的数据和表达式，不止整形和等式.同时，可以用let进行局部赋值。

let vegetable = "red pepper"
switch vegetable {
case "celery":
    print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
    print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
    print("Is it a spicy \(x)?")
default:
    print("Everything tastes good in soup.")
}

for-in:

let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}
print(teamScore)

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
        }
    }
}
print(largest)

while:

var n = 2
while n < 100 {
    n = n * 2
}
print(n)
 
var m = 2
repeat {
    m = m * 2
} while m < 100
print(m)

for:可以用”..<”来局部遍历索引。

var total = 0
for i in 0..<4 {
    total += i
}
print(total)

Functions and Closures

func:

用“->”来定义返回值:

func greet(person: String, day: String) -> String {
    return "Hello \(person), today is \(day)."
}
greet(person: "Bob", day: "Tuesday")

参数前可以设置别名，或者用“_”表示别名为空:

func greet(_ person: String, on day: String) -> String {
    return "Hello \(person), today is \(day)."
}
greet("John", on: "Wednesday")

参数可以定义成不定数的:

func sumOf(numbers: Int...) -> Int {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return sum
}
sumOf()
sumOf(numbers: 42, 597, 12)

返回值可以用名称或者数字做索引:

func calculateStatistics(scores: [Int]) -> (min: Int, max: Int, sum: Int) {
    ...
    return (min, max, sum)
}
let statistics = calculateStatistics(scores: [5, 3, 100, 3, 9])
print(statistics.sum)
print(statistics.2)

Func可以嵌套：

func returnFifteen() -> Int {
    var y = 10
    func add() {
        y += 5
    }
    add()
    return y
}
returnFifteen()

Func可以作为参数和返回值：

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(list: numbers, condition: lessThanTen)

func makeIncrementer() -> ((Int) -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)

Closure

Closure用“{}”包含，并用in分割参数返回值和具体实现:

{
    (number: Int) -> Int in
    let result = 3 * number
    return result
}

如果Closure的类型已经确定，可以更精简地写:

1 2	let mappedNumbers = numbers.map({ number in 3 * number }) print(mappedNumbers)

除了用名字，也可以用数字索引来表示参数:

1 2	let sortedNumbers = numbers.sorted { $0 > $1 } print(sortedNumbers)

Objects and Classes

Classes:

定义:

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

注意，Class的每个属性值都需要赋值，可以在定义时，也可以在构造函数中。

继承和重写:

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()

Get/Set:(可以用newValue指代参数值)

var perimeter: Double {
	get {
   		return 3.0 * sideLength
   	}
   set {
       sideLength = newValue / 3.0
   }
}

WillSet/DidSet:(在Set执行前后会被调用)

var square: Square {
	willSet {
   		triangle.sideLength = newValue.sideLength
   }
   didSet {
   		print(oldValue.sideLength)
   }
}

Objects:

对于是Optional类型的对象，可以用“?”来进行判断，如果值为nil，则结果直接为nil，否则为具体值。但是赋值式左边的类型是Optional类型。

1 2	let optionalSquare: Square? = Square(sideLength: 2.5, name: "optional square") let sideLength = optionalSquare?.sideLength

Enumerations and Structures

Enumerations:

Enum的Raw Values的类型，可以是Int, Float以及String。Int类型的默认从0开始，也可以强制设置为其他。

enum Rank: Int {
    case 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.rawValue)
        }
    }
}
let ace = Rank.ace
let aceRawValue = ace.rawValue

Raw Values类型也可以不设置:

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enum Suit {
    case spades, hearts, diamonds, clubs
}

可以直接用init?(rawValue:)来创造一个实例：

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if let convertedRank = Rank(rawValue: 3) {
    let threeDescription = convertedRank.simpleDescription()
}

还可以添加参数：

enum ServerResponse {
    case result(String, String)
    case failure(String)
}
 
let success = ServerResponse.result("6:00 am", "8:09 pm")
let failure = ServerResponse.failure("Out of cheese.")
 
switch success {
case let .result(sunrise, sunset):
    print("Sunrise is at \(sunrise) and sunset is at \(sunset).")
case let .failure(message):
    print("Failure...  \(message)")
}

Structs

Structs跟Classes的区别在于：Structs都是值传递，Classes都是引用传递。

struct Card {
    var rank: Rank
    var suit: Suit
    func simpleDescription() -> String {
        return "The \(rank.simpleDescription()) of \(suit.simpleDescription())"
    }
}
let threeOfSpades = Card(rank: .three, suit: .spades)
let threeOfSpadesDescription = threeOfSpades.simpleDescription()

Protocols and Extensions

Protocols

protocol ExampleProtocol {
    var simpleDescription: String { get }
    mutating func adjust()
}

Classed，Enumerations, Structs都可以适配Protocols:

class SimpleClass: ExampleProtocol {
    var simpleDescription: String = "A very simple class."
    var anotherProperty: Int = 69105
    func adjust() {
        simpleDescription += "  Now 100% adjusted."
    }
}
var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription
 
struct SimpleStructure: ExampleProtocol {
    var simpleDescription: String = "A simple structure"
    mutating func adjust() {
        simpleDescription += " (adjusted)"
    }
}
var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription

注意:mutating关键字在Structs中使用，用于标识会修改Structs元素，而Classes不用，Classes的方法本来就可以修改Classes。

Protocols可以当类型使用：

1 2	let protocolValue: ExampleProtocol = a print(protocolValue.simpleDescription)

Extensions

Extensions用于给一个已有的类型添加功能，可以结合Extensions和Protocol一起使用：

extension Int: ExampleProtocol {
    var simpleDescription: String {
        return "The number \(self)"
    }
    mutating func adjust() {
        self += 42
    }
}
print(7.simpleDescription)

Error Handling

Error定义：

enum PrinterError: Error {
    case outOfPaper
    case noToner
    case onFire
}

用throw来抛出异常，throws关键字来标识Func:

func send(job: Int, toPrinter printerName: String) throws -> String {
    if printerName == "Never Has Toner" {
        throw PrinterError.noToner
    }
    return "Job sent"
}

用do-catch来捕获异常,在do中用try来标识可能抛出异常的地方:

do {
    let printerResponse = try send(job: 1040, toPrinter: "Bi Sheng")
    print(printerResponse)
} catch {
    print(error)
}

多catch:

do {
    let printerResponse = try send(job: 1440, toPrinter: "Gutenberg")
    print(printerResponse)
} catch PrinterError.onFire {
    print("I'll just put this over here, with the rest of the fire.")
} catch let printerError as PrinterError {
    print("Printer error: \(printerError).")
} catch {
    print(error)
}

用try?来转换结果为Optional，如果有异常，则结果为nil，否则则为实际值:

1 2	let printerSuccess = try? send(job: 1884, toPrinter: "Mergenthaler") let printerFailure = try? send(job: 1885, toPrinter: "Never Has Toner")

用defer来定义在Func中其他代码都执行结束后，执行的代码(类似finally):

var fridgeIsOpen = false
let fridgeContent = ["milk", "eggs", "leftovers"]
 
func fridgeContains(_ food: String) -> Bool {
    fridgeIsOpen = true
    defer {
        fridgeIsOpen = false
    }
    
    let result = fridgeContent.contains(food)
    return result
}
fridgeContains("banana")
print(fridgeIsOpen)

Generics

用““来定义Generics类型：

func makeArray<Item>(repeating item: Item, numberOfTimes: Int) -> [Item] {
    var result = [Item]()
    for _ in 0..<numberOfTimes {
        result.append(item)
    }
    return result
}
makeArray(repeating: "knock", numberOfTimes:4)

Classed，Enumerations, Structs都定义Generics类型:

enum OptionalValue<Wrapped> {
    case none
    case some(Wrapped)
}
var possibleInteger: OptionalValue<Int> = .none
possibleInteger = .some(100)

用where关键字在Func后，来列出要求，例如，要求类型必须适配Protocol，要求两种类型必须相同，要求一个Class必须有一个指定的父类:

func anyCommonElements<T: Sequence, U: Sequence>(_ lhs: T, _ rhs: U) -> Bool
    where T.Iterator.Element: Equatable, T.Iterator.Element == U.Iterator.Element {
        for lhsItem in lhs {
            for rhsItem in rhs {
                if lhsItem == rhsItem {
                    return true
                }
            }
        }
        return false
}
anyCommonElements([1, 2, 3], [3])

<T: Equatable> 等同于 <T> ... where T: Equatable>