Swift 知识点速查

var greeting: String = "Hello"
var numberOfToys: Int = 8
var isMorning: Bool = true
var price: Double = 8.99

var apples = 6
print("I have \(apples) apples!")
// 打印: I have 6 apples!

let myLongString = """
Swift?
这是我最喜欢的语言！
"""

// 这一行表示 Swift 中的注释。
/*
这都被注释掉了。
没有一个会跑！
*/

let player = (name: "Maya", level: 5)
let (currentName, curLevel) = player
print("\(currentName): level \(curLevel)")
// 打印: Maya: level 5

// MARK: - 查看设置

MARK 可用于在栏中显示评论

// TODO: 更新逻辑以适应数据更改

TODO 用于显示需要完成的事情的提醒

// FIXME: 修复对现有条目进行更改时的故障行为

FIXME 用于显示需要修复的内容的提醒

变量用 var 声明：

var greeting = "你好"
var numberOfToys = 8
var isMorning = true

为了清楚起见，变量声明可以包含类型注释：

var greeting: String = "你好"
var numberOfToys: Int = 8
var isMorning: Bool = true

变量是可变的。 它们的值可以改变：

var numberOfToys: Int = 8
numberOfToys += 1
print(numberOfToys) // 打印“9”

常量用 let 声明：

let greeting = "Hello"
let numberOfToys = 8
let isMorning = true

为清楚起见，常量声明可以包含类型注释：

let greeting: String = "Hello"
let numberOfToys: Int = 8
let isMorning: Bool = true

常量是不可变的。它们的值不能改变：

let numberOfToys: Int = 8
numberOfToys += 1
// ❌ 错误：numberOfToys 不可变

var distance = 5 {
  didSet {
    print("距离设置为 \(distance)")
    print("它的旧值是： \(oldValue)")
  }
}
distance = 10 // 打印: 距离将被设置 10
              // 打印: 它的旧值是：5

var distance = 5 {
  willSet(newDistance) {
    print("距离将设置为 \(newDistance)")
  }
  didSet {
    print("距离设置为 \(distance)")
    print("它的旧值是： \(oldValue)")
  }
}
distance = 10

var halloween = true 
if halloween {
  print("不给糖就捣蛋！")
}
// 打印: 不给糖就捣蛋！ 
if 5 > 3 {
  print("5 大于 3")
} else {
  print("5 不超过 3")
}
// 输出: "5 大于 3"

var turbulence = false

if turbulence {
  print("请坐好。")
} else {
  print("你可以自由地四处走动。")
}
// 打印: 你可以自由地四处走动。

var weather = "rainy"
if weather == "sunny" {
  print("拿点防晒霜")
} else if weather == "rainy" {
  print("拿一把雨伞")
} else if weather == "snowing" {
  print("穿上你的雪地靴")
} else {
  print("无效天气")
}
// 打印: 拿一把雨伞

5 > 1          // true 
6 < 10         // true 
2 >= 3         // false
3 <= 5         // true
"A" == "a"     // false
"B" != "b"     // true

• < 小于
• > 大于
• <= 小于或等于
• >= 大于或等于
• == 等于
• != 不等于

var driverLicense = true

driverLicense 
    ? print("驾驶座") : print("乘客座位") 
// 打印: 驾驶座

var secondaryColor = "green"

switch secondaryColor {
  case "orange":
    print("红色和黄色的混合")
  case "purple":
    print("红色和蓝色的混合") 
  default: 
    print("这可能不是辅助颜色") 
}
// 打印: 蓝色和黄色的混合

let year = 1905
var artPeriod: String

switch year {
  case 1860...1885:
    artPeriod = "印象派"
  case 1886...1910:
    artPeriod = "后印象派"
  default:  
    artPeriod = "未知"
}
// 打印: 后印象派

let service = "Seamless"

switch service {
  case "Uber", "Lyft":
    print("旅行")
  case "DoorDash", "Seamless", "GrubHub":
    print("餐厅送餐")
  case "Instacart", "FreshDirect":
    print("杂货配送")
  default: 
    print("未知服务")
}
// 打印: 餐厅外卖

let num = 7

switch num {
  case let x where x % 2 == 0:
    print("\(num) 是偶数")
  case let x where x % 2 == 1:
    print("\(num) 奇数")
  default:
    print("\(num) 无效")
}

// 打印: 7 奇数

!true          // false
!false         // true

true && true    // true
true && false   // false 
false && true   // false 
false && false  // false

true || true    // true
true || false   // true
false || true   // true 
false || false  // false

!false && true || false // true

!false && true 首先计算并返回 true 然后，表达式，true || false 评估并返回最终结果 true

false || true && false  // false

true && false 首先计算返回 false 然后，表达式，false || false 评估并返回最终结果 false

// 没有括号：
true || true && false || false
// ---->  true 

// 带括号：
(true || true) && (false || false)
// ---->  false 

func greet(name: String?) {
  guard let unwrapped = name else {
    print("Hello guest!")
    return
  }
  print("Hello \(unwrapped)!")
}
greet(name: "Asma") // 输出：Hello Asma!
greet(name: nil)    // 输出：Hello guest!

let zeroToThree = 0...3
// zeroToThree: 0, 1, 2, 3

for oddNum in stride(from: 1, to: 5, by: 2) {
  print(oddNum)
}
// 打印: 1
// 打印: 3

for char in "hehe" {
  print(char)
}
// 打印: h
// 打印: e
// 打印: h
// 打印: e

for num in 0...5 {
  if num % 2 == 0 {
    continue
  }
  print(num)
}
// 打印: 1
// 打印: 3
// 打印: 5

continue 关键字将强制循环继续进行下一次迭代

for char in "supercalifragilistice" {
  if char == "c" {
    break
  }
  print(char)
}
// 打印: s
// 打印: u
// 打印: p
// 打印: e
// 打印: r

for _ in 1...3 {
  print("Olé")
}
// 打印: Olé
// 打印: Olé
// 打印: Olé

var counter = 1
var stopNum = Int.random(in: 1...10)

while counter < stopNum {
  print(counter)
  counter += 1
}
// 循环打印，直到满足停止条件

while 循环接受一个条件，并在所提供的条件为 true 时持续执行其主体代码。如果条件从不为假，则循环将继续运行，程序将陷入无限循环

var scores = [Int]()
// 数组为空：[]

var grocery = ["🥓", "🥞", "🍪", "🥛", "🍊"]
print(grocery.count)
// 打印: 5

// 使用类型推断：
var snowfall = [2.4, 3.6, 3.4, 1.8, 0.0]
// 明确类型：
var temp: [Int] = [33, 31, 30, 38, 44]

var gymBadges = ["Boulder", "Cascade"]
gymBadges.append("Thunder")
gymBadges += ["Rainbow", "Soul"]
// ["Boulder", "Cascade", "Thunder",
//   "Rainbow", "Soul"]

var moon = ["🌖", "🌗", "🌘", "🌑"]
moon.insert("🌕", at: 0)
// ["🌕", "🌖", "🌗", "🌘", "🌑"]

moon.remove(at: 4)
// ["🌕", "🌖", "🌗", "🌘"]

var employees = ["小王", "张三", "王五"]
for person in employees {
  print(person)
}
// 打印: 小王
// 打印: 张三
// 打印: 王五

var paintingsInMOMA: Set = [
  "The Dream",
  "The Starry Night",
  "The False Mirror"
]

我们可以使用集合(Set)来存储相同数据类型的唯一元素

var team = Set<String>()

print(team)
// 打印: [] 

var vowels: Set = ["a", "e", "i", "o","u"]

要创建一个填充有值的集合，请在赋值运算符之前使用 Set 关键字。

var cookieJar: Set = [
  "Chocolate Chip",
  "Oatmeal Raisin"
]
// 添加一个新元素
cookieJar.insert("Peanut Butter Chip")

var oddNumbers: Set = [1, 2, 3, 5]

// 移除现有元素
oddNumbers.remove(2)
// 删除所有元素
oddNumbers.removeAll()

var names: Set = ["Rosa", "Doug", "Waldo"]
print(names.contains("Lola")) //打印: false

if names.contains("Waldo"){
  print("There's Waldo!")
} else {
  print("Where's Waldo?")
}
// 打印: There's Waldo!

var recipe: Set = ["蛋", "面粉", "糖"]

for ingredient in recipe {
  print ("在配方中包含\(ingredient)")
}

var emptySet = Set<String>()
print(emptySet.isEmpty)  // 打印: true

var populatedSet: Set = [1, 2, 3]
print(populatedSet.isEmpty) // 打印: false

var band: Set = ["张三", "王五", "赵六"]

print("乐队有 \(band.count) 名演奏者。")
// 打印: 乐队有 4 名演奏者。

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]

var setC = setA.intersection(setB)
print(setC)  // 打印: ["D", "C"]

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]

var setC = setA.union(setB)
print(setC) 
// 打印: ["B", "A", "D", "F", "C", "E"]

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D", "E", "F"]

var setC = setA.symmetricDifference(setB)
print(setC) 
// 打印: ["B", "E", "F", "A"]

var setA: Set = ["A", "B", "C", "D"]
var setB: Set = ["C", "D"]

var setC = setA.subtracting(setB)
print(setC) 
// 打印: ["B", "A"]

var dictionaryName = [
  "Key1": "Value1",
  "Key2": "Value2",
  "Key3": "Value3"
]

成对数据或键值对的无序集合

var fruitStand = [
  "Coconuts": 12,
  "Pineapples": 12,
  "Papaya": 12
]

每个键都是唯一的，即使它们都包含相同的值

var numberOfSides = [
  "triangle": 3,
  "square": 4,
  "rectangle": 4
]

仅包含 String 键和 Int 值

var employeeID = [
  "Hamlet": 1367,
  "Horatio": 8261,
  "Ophelia": 9318
]

// 初始化器语法：
var yearlyFishPopulation = [Int: Int]()

// 空字典字面量语法：
var yearlyBirdPopulation: [Int: Int] = [:]

var pronunciation = [
  "library": "lai·breh·ree",
  "apple": "a·pl"
]
// 新键：“programming”，新值：“prow·gra”
pronunciation["programming"] = "prow·gra"

var bakery = [String:Int]()

// 检查字典是否为空
print(bakery.isEmpty)    // 打印 true
bakery["Cupcakes"] = 12
// 检查字典是否为空
print(bakery.isEmpty)    // 打印 false

var fruitStand = [
  "Apples": 12,
  "Oranges", 17
]
print(fruitStand.count)  // 打印: 2

var hex = [
  "red": "#ff0000",
  "yellow": "#ffff00",
  "blue": "#0000ff",
]

print("蓝色十六进制代码 \(hex["blue"])")
// 打印: 蓝色十六进制代码 Optional("#0000ff")

if let redHex = hex["red"] {
  print("红色的十六进制代码 \(redHex)")
}
// 打印: 红色的十六进制代码 #ff0000

将键值对的值分配给变量将返回一个可选值。要提取值，请使用可选的展开

var emojiMeaning = [
  "🤔": "Thinking Face",
  "😪": "Sleepy Face",
  "😵": "Dizzy Face"
]
// 遍历键和值
for (emoji, meaning) in emojiMeaning {
  print("\(emoji)被称为'\(meaning)Emoji'")
}
// 仅通过键迭代
for emoji in emojiMeaning.keys {
  print(emoji)
}
// 仅通过值迭代
for meaning in emojiMeaning.values {
  print(meaning)
}

func washCar() -> Void {
  print("Soap")
  print("Scrub")
  print("Rinse")
  print("Dry")
}

func greetLearner() {
 print("欢迎来到 IT开发知识!")
}
// 函数调用：
greetLearner()
// 打印: 欢迎来到 IT开发知识!

let birthYear = 1994
var currentYear = 2020

func findAge() -> Int {
  return currentYear - birthYear
}

print(findAge()) // 打印: 26

func findDiff(_ a: Int, b: Int) -> Int {
  return a - b
}

print(findDiff(6, b: 4)) // 打印: 2

func findSquarePerimet(side: Int) -> Int {
  return side * 4
} 

let perimeter = findSquarePerimet(side: 5)
print(perimeter) // 打印: 20

// Parameter: side
// Argument:  5

func nextTotalSolarEclipse() -> String {
  "April 8th, 2024 🌎"
}

print(nextTotalSolarEclipse())
// 打印: April 8th, 2024 🌎

func greet(person: String = "guest") {
  print("Hello \(person)")
}
greet() // Hello guest
greet(person: "Aliya") // Hello Aliya

func totalStudent(data: String...) -> Int {
  let numStudents = data.count
  return numStudents
}

print(totalStudent(data: "王五", "张三"))
// 打印: 2

func getFirstInitial(from name: String?) -> String? {
  return name?.first
}

函数可以接受可选类型并返回可选类型。当一个函数不能返回请求类型的合理实例时，它应该返回 nil

struct Building {
  var address: String
  var floors: Int

  init(address: String, floors: Int) {
    self.address = address
    self.floors = floors
  }
}

结构或结构用于以编程方式在代码中表示现实生活中的对象。结构是使用 struct 关键字创建的，后跟其名称，然后是包含其属性和方法的主体

struct Car {
  var numOfWheels = 4
  var topSpeed = 80
}

var reliantRobin = Car(numOfWheels: 3)

print(reliantRobin.numOfWheels) // 打印: 3
print(reliantRobin.topSpeed)    // 打印: 80

struct Person {
  var name: String
  var age: Int

  init(name: String, age: Int) {
    self.name = name
    self.age = age
  }
}

// Person 实例：
var morty = Person(name: "张三", age: 14)

print(type(of: "abc")) // 打印: String
print(type(of: 123))   // 打印: 123

struct Dog {
  func bark() {
    print("Woof")
  }
}
let fido = Dog()
fido.bark() // 打印: Woof

class Person {
  var name = ""
  var age = 0
}

var sonny = Person()
// sonny 现在是 Person 的一个实例

var ferris = Student()

ferris.name = "Ferris Bueller"
ferris.year = 12
ferris.gpa = 3.81
ferris.honors = false

使用数据类型

class Student {
  var name: String
  var year: Int
  var gpa: Double
  var honors: Bool
}

使用默认属性值

class Student {
  var name = ""
  var gpa = 0.0
  var honors = false
}

struct Resolution {
  var width = 0
  var height = 0
}
class VideoMode {
  var resolution = Resolution()
  var interlaced = false
  var frameRate = 0.0
  var name: String?
}

Resolution 结构定义和 VideoMode 类定义仅描述 Resolution 或 VideoMode 的外观，创建结构或类的实例：

let resolution = Resolution(width: 1920)
let someVideoMode = VideoMode()

enum Day {
  case monday
  case tuesday
  case wednesday
  case thursday
  case friday
  case saturday
  case sunday
}

let casualWorkday: Day = .friday

enum Dessert {
  case cake(flavor: String)
  case vanillaIceCream(scoops: Int)
  case brownie
}

let customerOrder: Dessert = .cake(flavor: "红色天鹅绒")
switch customerOrder {
  case let .cake(flavor):
    print("你点了一个 \(flavor) 蛋糕")
  case .brownie: 
    print("你点了一块巧克力蛋糕")
}
// 打印: "你点了一个红色天鹅绒蛋糕"

enum Season: CaseIterable {
  case winter
  case spring
  case summer
  case fall
}

for season in Season.allCases {
  print(season)
}

添加对 CaseIterable 协议的一致性以访问 allCases 属性，该属性返回枚举的所有案例的数组

enum Beatle: String {
  case john, paul, george, ringo
}

print("披头士是 \(Beatle.john.rawValue).")
// 打印: 披头士是 john.

enum Dessert {
  case cake(flavor: String)
  case vanillaIceCream(scoops: Int)
  case brownie
}

let order: Dessert = .cake(flavor: "红色天鹅绒")

enum Hello: String {
  case english = "Hello"
  case japanese = "你好呀！"
  case emoji = "👋"
}
let hello1 = Hello(rawValue: "你好呀！")
let hello2 = Hello(rawValue: "Привет")
print(hello1) // Optional(Hello.japanese)
print(hello2) // nil

enum ShirtSize: String {
  case small = "S"
  case medium = "M"
  case large = "L"
  case extraLarge = "XL"
  var description: String {
    return "这件衬衫尺码是 \(self.rawValue)"
  }
}