基本数据类型
- 使用 let 定义常量
let myConstant = 42
- 使用var 定义变量
var myVariable = 42
myVariable = 50
- 如果有初始化，你可以指定变量类型或者让系统自己去推断
let implicitInteger = 70
let implicitDouble = 70.0
let explicitDouble: Double = 70
- 如果没有初始化，你要必须指定变量类型
var numb:Double
- 在Swift 中，字符串是基本类型
let label = "The width is "
width = 94
- 如何实现数据之间的相互转换
let 94
let widthLabel:String = String(width)
- 使用最简单的方式将其他数据类型变成字符串
let apples = 3
let oranges = 5
let fruitSummary = "I have \(apples + oranges) pieces of fruit."
- 数组也是基本类型，不再是OC中的引用类型了
var shoppingList = ["catfish","water",152)">"tulips",152)">"blue paint"]
shoppingList[1] = "bottle of water"
- 定义一个空数组
let emptyArray = [String]()
let emptyArray:[String] = []
- 字典也是基本类型
var occupations = [
"Malcolm": "Captain",152)">"Kaylee": "Mechanic",]
- 将数组清空
var shopingList1 = ["1",152)">"2"]
shopingList1 = [] // 如果你这个类型,是系统可以推断的类型,你可以这样清空数组或者初始化
- 定义一个空字典
let emptyDictionary = [String: Float]()
let emptyDictionary:[String: Float] = [:]
- 清空字典
dictionary = [1:"2"]
dictionary = [:]
可选值
let nickName: String? = nil
"?" ：你的变量可能为nil，或者你可能将nil赋值给它，需要给变量定义的时候加上"?"，否则一旦你将nil赋值给没有加"?"的变量，编译就会报错。
举个例子理解一下，我们假如有一个盒子，盒子是一个存在的物体，Swift不允许有空值出现，那我们怎么办呢？就需要把空值装到一个盒子里面，系统检查的时候，发现有一个盒子，哦好的，检测通过，但是如果你把盒子打开系统就会报错。
运行下面的代码:
let nickName: String? = "酷走天涯"
print(nickName)
结果:
Optional("酷走天涯")
发现有个Optional 就说明这个变量被包着，那么怎么才能不让它包裹着呢? 很简单，给变量加一个"!"
print(nickName!)
运行:
酷走天涯
我们还有一种解包的方式
String? = nil
let fullName: String = "XUJIE"
let informalGreeting = "Hi \(nickName ?? fullName)"
print(informalGreeting)
运行
Hi XUJIE
如果第一个解包值发现为nil,则使用第二值
控制流
- for ... in 循环
// 遍历数组
let individualscores = [75,43,152)">103,152)">87,152)">12]
var teamscore = 0
for score in individualscores {
if score > 50 {
teamscore += 3
} else {
teamscore += 1
}
}
print(teamscore)
// 遍历 字典
let interestingNumbers = [
"Prime": [2,152)">3,152)">5,152)">7,152)">11,152)">13],152)">"Fibonacci": [1,152)">8],152)">"Square": [4,152)">9,152)">16,152)">25],]
var largest = for (kind,numbers) in interestingNumbers {
for number in numbers {
if number > largest {
largest = number
}
}
}
// 还可以这样使用循环
var total = 0
for i in 0..<4 {
total += i
}
print(total)
- Switch
let vegetable = "red pepper"
switch vegetable {
case "celery":
print("Add some raisins and make ants on a log.")
"cucumber",152)">"watercress":
"That would make a good tea sandwich.")
case let z where z.hasSuffix("pepper"):
"Is it a spicy \(z)?")
default:
"Everything tastes good in soup.")
}
注意 z 什么 随便写个变量名就可以了
- while 循环
var n = 2
while n < 100 {
n = n * 2
}
print(n)
- repeat ...while
var m = 2
repeat {
m = m * 2
} while m < 100
print(m)
函数和闭包
func greet(person: String,day: String) -> String {
return "Hello \(person),today is \(day)."
}
greet(person: "Bob",210)">day: "Tuesday")
- 缺省参数名
func greet(_ person: String,152)">_ day: String) ->
}
greet("John",152)">"Wednesday")
- 返回值可以是元祖类型
func calculateStatistics(scores: [Int]) -> (min: Int,210)">max: Int,210)">sum: Int) {
min = scores[0]
max = scores[sum = in scores {
if score > max {
max = score
} else if score < min {
min = score
}
sum += score
}
return (min,210)">max,210)">sum)
}
let statistics = calculateStatistics(scores: [100,152)">9])
print(statistics.sum)
print(statistics.2)
- 定义多个类型相同的参数
func sumOf(numbers: Int...) -> Int {
var sum = in numbers {
sum += number
}
return sum
}
sumOf()
sumOf(numbers: 42,152)">597,152)">12)
- 函数嵌套使用
returnFifteen() -> Int {
var y = 10
add() {
y += 5
}
// 方法内部定义方法,声明周期为方法
add()
return y
}
returnFifteen()
- 函数当返回值
func makeIncrementer() -> ((Int) -> Int) { func addOne(number: Int) -> Int {
return 1 + number
}
return addOne
}
var increment = makeIncrementer()
increment(7)
- 函数当参数
hasAnyMatches(list: [Int],condition: (Int) -> Bool) -> Bool {
for item in list {
if condition(item) {
return true
}
}
return false
}
lessthanTen(number: Int) -> Bool {
return number < 10
}
var numbers = [20,152)">19,152)">12]
hasAnyMatches(list: numbers,condition: lessthanTen)
对象和类
- 定义一个类
class Shape {
var numberOfSides = 0
func simpleDescription() -> String {
"A shape with \(numberOfSides) sides."
}
}
NamedShape {
var numberOfSides: Int = 0
var name: String
// 初始化方法
init(name: String) {
self.name = name
}
// 成员方法定义
simpleDescription() -> String {
"A shape with \(numberOfSides) sides."
}
}
- 继承
Square: NamedShape {
var sideLength: Double // 如果不是可选类型 必须在初始化方法中初始化
init(sideLength: Double,name: String) {
self.sideLength = sideLength
super.init(name: name) // 调用父类的初始化方法
numberOfSides = 4 // 给父类的属性赋值之前必须先调用父类的初始化方法
}
area() -> Double {
return sideLength * sideLength
}
// 重写父类的方法
override String {
"A square with sides of length \(sideLength)."
}
}
- setter 和 getter
EquilateralTriangle: NamedShape {
var sideLength: Double = 0.0 // 定一个属性
init(sideLength: Double,name: String) {
self.sideLength = sideLength
super.init(name: name)
numberOfSides = 3
}
// 这个是setter 和geterr方法的定义
var perimeter: Double {
get {
3.0 * sideLength
}
set {
sideLength = newValue / 3.0
}
}
override func simpleDescription() -> String {
"An equilateral triangle with sides of length \(sideLength)."
}
}
- 观察属性
class TriangleAndSquare {
// 定一个三角形对象
var triangle: EquilateralTriangle {
willSet {
square.sideLength = newValue.sideLength
}
}
// 定一个一个正方形对象
var square: Square {
willSet {
triangle.sideLength = newValue.sideLength
}
}
// 通过检测属性,我们让两个对象的边保持一样长
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")
print(triangleAndSquare.square.sideLength)
print(triangleAndSquare.triangle.sideLength)
triangleAndSquare.square = Square(sideLength: 50,152)">"larger square")
print(triangleAndSquare.triangle.sideLength)
运行结果
10.0
10.0
50.0
枚举类型
- 定义
enum Rank: Int { // Int 设置枚举值的类型
// 定义枚举值设置值
case ace = 1
// 可以case 后面一次定义多个枚举值
case two,three,four,five,six,seven,eight,nine,ten
case jack,queen,king
// 定义函数 如果多人合作的时候,可以使用这个让别人更加了解你定义的属性的含义
String {
switch self { // self 就是这个枚举本身
case .ace:
"ace"
case .jack:
"jack"
case .queen:
"queen"
case .king:
"king"
default:
return String(self.rawValue)
}
}
}
// 使用
let ace = Rank.ace
let aceRawValue = ace.rawValue
问题1 如何想OC 一样使用 | 或操作呢?
结构体
- struct Card {
// 定义结构体
var rank: Rank
var suit: Suit
// 结构体内可以定义方法
"The \(rank.simpleDescription()) of \(suit.simpleDescription())"
}
}
- 使用
- 给类添加协议
letthreeOfSpades = Card(rank: .three,suit: .spades) let threeOfSpadesDescription = threeOfSpades.simpleDescription()
协议
- protocol ExampleProtocol {
var simpleDescription: String { get }
mutating adjust()
}
SimpleClass: ExampleProtocol {
"A very simple class."
var anotherProperty: 69105
adjust() {
simpleDescription += " Now 100% adjusted."
}
}
- 给结构体添加协议
SimpleStructure: "A simple structure"
" (adjusted)"
}
}
- 定义一个协议变量
let protocolValue: ExampleProtocol = a
print(protocolValue.simpleDescription)
扩展
extension Int: ExampleProtocol {
"The number \(self)"
}
adjust() {
self += 42
}
}
print(7.simpleDescription)
错误操作
PrinterError: Error {
case outOfPaper
case noToner
case onFire
}
send(job: Int,toPrinter printerName: String) throws -> if printerName == "Never Has Toner" {
throw PrinterError.noToner
}
"Job sent"
}
- 捕捉异常
do {
let printerResponse = try send(job: 1040,toPrinter: "Bi Sheng")
print(printerResponse)
} catch {
print(error)
}
- 异常分类处理
1440,152)">"Gutenberg")
catch PrinterError.onFire {
print("I'll just put this over here,with the rest of the fire.")
} catch let printerError as PrinterError {
"Printer error: \(printerError).")
} catch {
print(error)
}
总结
Swift 的基本语法已经了解完毕,但这只是些简单的东西,如果Swift只是这些东西,那我们就没有学习的必要了,Swift的灵活性,优秀的设计模式,从上面的内容体现不出来,我会在后面几篇文章中,阐述它的高级用法!
原文地址：https://www.jb51.cc/swift/321671.html
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