Swift語言基礎

更新時間：2020-03-24
Swift版本：Swift 5

1.1 Swift 和 Playground簡介

/* 1.1 Swift 和 Playground簡介
 * 使用XCode新建playground項目，複製一下代碼查看效果！
 */
var str = "Hello, playground"
var a = 12,b=21
print(str)
print(a+b)

1.2 常量、變量和數據類型

數據類型

let name = "John" // 常量
var age = 20      // 變量
let printStr = "name:\(name),\(age)" // 字符串插值

// 定義一個類
struct Person{
    let firstName: String
    let lastName: String
    
    func sayHello() {
        print("Hello there!My name is \(firstName) \(lastName).")
    }
}

// 初始化類的對象實列
let person = Person(firstName: "xu", lastName: "yingchun") // 字面量
person.sayHello()

類型安全和類型推斷

let playerName = "name"
var playerScore = 1000
var numberWitchDicimals = 17.5
var gameOver = false

// playerName = playerScore
// playerScore = numberWitchDicimals
// Will be flagged for mismatched type, will not compile.

let cityName: String = "San Francisco"
let pi: Double = 3.1415927
let number: Double = 3
print(number)

1.3 運算符

// 分配值
var shoeSize = 8
shoeSize = 9 // Reassigns shoeSize to 9

// 基本算數
var opponentScore = 3 * 8 // opponentScore has a value of 24
var myScore = 100 / 4     // myScore has a value of 25
var totalScore = opponentScore * myScore
myScore += 3
myScore -= 5
myScore *= 2
myScore /= 2
var x = 2,y = 3,z = 5
x + y * z // Equals 17

let a1 = 3,b1 = 0.1415927
let pi1 = Double(a1) + b1 // 數值型類型轉換

1.4 控制流程

// if條件
let temperature = 100
if temperature >= 100 {
    print("The water is boiling.")
}else if temperature < 0 {
    print("The water is cold.")
}else{
    print("The water is not boiling.")
}

// switch語句
let numberOfWheels = 2
switch numberOfWheels{
case 1:
    print("Unicycle") // 不需要break，會直接跳出，如果要向下執行，添加fallthrough關鍵字
case 2:
    print("Bicycle")
default:
    print("That's a lot of wheels!")
}

// switch語句支持字符串
let character = "z"
switch character{
case "a","e","i","o","u":
    print("This character is a vowel.")
default:
    print("This character is a consonat.")
}

// switch語句支持區間匹配
let distance = 100
switch distance {
case 0...9:
    print("Your destination is close.")
case 10...99:
    print("Your destination is a medium distance from here.")
default:
    print("Are you sure you want to travel this far?")
}

1.5 循環

for

// Swift5不支持for循環？，作者使用for-in代替之

for var i:=0;i<10;i++{
print(i)
}

for-in

for index in 1..<5 {
    print("This is number\(index)")
}
let names2 = ["Joseph", "Cathy", "Winston"]
for item in names2 {
    print("Hello \(item)")
}
let vehicles = ["unicycle": 1, "bicycle":2]
for (key,value) in vehicles {
    print("A \(key) has \(value) wheels")
}

while

var numberOfLives = 3
var stillAlive = true

while stillAlive {
    numberOfLives -= 1
    if numberOfLives == 0{
        break
    }
}

1.6 集合

數組

var names: [String] = ["Anne","Gray"]
var numbers = [1, -3, 24, 114]
if numbers.contains(24){
    print("There is a 24")
}
numbers[1] = 23
numbers.append(2) // 追加
numbers+=[1,3] // 一次追加多個元素
numbers.insert(31, at: 0)
numbers.remove(at: 0)
let array1 = [1,2,3]
let array2 = [4,5,6]
let arrayAll = [array1,array2] // [[1,2,3],[4,5,6]] // 二維數組

字典

var myDictionary = [String:Int]()
var myDictionary2 = Dictionary<String,Int>()
myDictionary["Oli"] = 399 //添加
if let oldValue = myDictionary.updateValue(200, forKey: "Oli") {//更新
    print("Richard's old value was \(oldValue)")
}
var scores = ["Richard": 500, "Luke": 100] //訪問字典
let players = Array(scores.keys) // ["Richard", "Luke"]
let points = Array(scores.values)// [500, 100]
if let myScore = scores["Luke"] {
    print(myScore)
}else{
    print("Not find")
}

1.7 字符串

let greeting = "Hello \"world\""
var myString = ""
if myString.isEmpty {
    print("The string is empty")
}
// 串聯和插值
myString = greeting + "yes"
let age1 = 30
let name1 = "Rick"
print("\(name1) is \(age1+5) years old")
// 字符串相等
if myString != greeting {
    print("The are not the same")
}
if greeting.contains("Hello") {
    print("Making an introduction")
}
print("the greeting len=\(greeting.count)")

1.8 函數

func displayPi(){
    print("3.1415927")
}
displayPi() // 調用

func triple(value: Int){
    let result = value * 3
    print("If you multiple \(value) by 3,you'll get \(result).")
}
triple(value: 20) // 帶參數

func triple2(_ value: Int){
    triple(value: value)
}
triple2(10)       // 自變量標籤，可省略參數標籤

// 默認參數值和
// 返回多個值
func multiple(_ firstNumber: Int, secondNumber: Int = 10) -> (a: Int,b: Int){
    return (firstNumber * secondNumber , secondNumber)
}
var multipleResult = multiple(2)
print("Return=\(multipleResult) a=\(multipleResult.a) b=\(multipleResult.b)")

1.9 枚舉

enum  MsgType{
    case Text
    case Image
    case Video
    case File
}

1.10 類

構造函數和析構

var stringInit = String.init() // ""
var integerInit = Int.init()   // 0

class Temperature{
    var celsius: Double
    
    // 帶一個參數的構造函數
    init(celsius: Double){
        self.celsius = celsius
    }
    
    // 可以重載，和java不同，可以通過參數名字區分開而不是參數數量
    init(fahrenheit: Double){
        self.celsius = (fahrenheit - 32) / 1.8
    }
    
    deinit{
        print("對象被消耗")
    }
}
var boiling = Temperature(fahrenheit: 212.0)
boiling = nil // 不再指向原來的對象，GC幫助我們自動銷燬該對象

屬性和方法

class Person{
    let maxAge: 200  // 常量
    var name: String // 變量
    static var numberOfPerson = 0 // 類（靜態）屬性
    
    // 對象（實例）方法
    func walk(){
        
    }
    
    // 類（靜態）方法，使用class修飾
    class func convert(){
        
    } 
}

繼承

class Scientist{
    func doSomeThing() {
    }
    
    // final 修飾的屬性和方法，子類不能重寫
    final func finalMethod(){
        
    }
}
class Geologist: Scientist{
    override func doSomeThing() {
        super.doSomeThing() // super調用父類方法
    }
}

計算屬性

class Temperature2{
    var celsius: Double
    var fahrenheit: Double{
        get{ // 變量可讀
            return celsius * 1.8 + 32
        }
        set{ // 變量可寫
            celsius = newValue / 1.8
        }
    }
}

屬性觀察器

struct StepCounter{
    var totalSteps: Int = 0 {
        willSet{
            print("About to set totalSteps to \(newValue)")
        }
        didSet{
            if totalSteps > oldValue{
                print("Added \(totalSteps - oldValue)")
            }
        }
    }
}
var stepCounter = StepCounter()
stepCounter.totalSteps = 40
stepCounter.totalSteps = 100

1.11 結構體

定義

注意：
結構體是值類型，類是引用類型。

struct Car{
    var make: String
    var year: Int = 0
    func startEngine() {}
    func drive() {}
}

var firstCar = Car(make: "Ford", year: 2013)
firstCar.startEngine()
firstCar.drive()

拷貝

var t1 = Temperature2(celsius: 2.0)
var t2 = t1
t2.celsius = 10.0 // 拷貝結構體，所以不會影響原結構體的值，和“類”的不同之處，如果分不清，全部使用Class即可。
print(t1.celsius)

1.12 協議（接口）

protocol CanFly {
    var mustBeSettable: Int { get set} // 必須實現可讀可寫的屬性
    
    class func someTypeMethod() // 類（靜態）方法
    func random() -> Double     // 對象（實例）方法
}

1.13 高級

可選鏈和類型轉換

class Residence{
    var numberOfRooms = 1
}

class Person{
    var residence: Residence? // 可爲nil
}

let john = Person()
let rootCount = john.residence!.numberOfRooms // 報錯
// 正確的寫法
if let roomCount = john.resindece?.numberOfRooms {
    print("房間數量爲：\(roomCount))")
}else{
    print("房間數量爲空")
}

閉包

func compare(a: String, b: String) -> Bool{
    return a > b
}

let namges = ["Bob","Alice","Barry","Ewa"]
var reversed = sorted(names,compare) // 排序
println(reversed)

// 閉包語法
//{(paremeters) -> returnType in
//   statements
//}

// 這裏可省略compare方法的定義，更簡潔
reversed = sorted(names,{(a: String, b: String) -> Bool in
   return a > b
})

// 可放在一行，可讀性不是很好，不是很推薦
reversed = sorted(names,{(a: String, b: String) -> Bool in return a > b })

泛型

struct Stack<T>{
    var items = [T]() // 一個數組
    
    mutating func push(item:T){
        items.append(item)
    }
    
    mutating func pop() -> T{
        return items.removeLast()
    }
}

var stackOfStrings = Stack<String>() // 初始化一個Stack<String>類型，注意類型是：Stack<String>，不是Stack
stackOfStrings.push("a")
stackOfStrings.push("b")
print(stackOfStrings.pop())

完整的Playground項目

import UIKit

/* 1.1 Swift 和 Playground簡介
 * 使用XCode新建playground項目，複製一下代碼查看效果！
 */
var str = "Hello, playground"
var a = 12,b=21
print(str)
print(a+b)

/* 1.2 常量、變量和數據類型 */
// 數據類型
let name = "John" // 常量
var age = 20      // 變量
let printStr = "name:\(name),\(age)" // 字符串插值

struct Person{
    let firstName: String
    let lastName: String
    
    func sayHello() {
        print("Hello there!My name is \(firstName) \(lastName).")
    }
}
let person = Person(firstName: "xu", lastName: "yingchun")
person.sayHello()

// 類型安全和類型推斷
let playerName = "name"
var playerScore = 1000
var numberWitchDicimals = 17.5
var gameOver = false

// playerName = playerScore
// playerScore = numberWitchDicimals
// Will be flagged for mismatched type, will not compile.

let cityName: String = "San Francisco"
let pi: Double = 3.1415927
let number: Double = 3
print(number)

/* 1.3運算符 */
// 分配值
var shoeSize = 8
shoeSize = 9 // Reassigns shoeSize to 9

// 基本算數
var opponentScore = 3 * 8 // opponentScore has a value of 24
var myScore = 100 / 4     // myScore has a value of 25
var totalScore = opponentScore * myScore
myScore += 3
myScore -= 5
myScore *= 2
myScore /= 2
var x = 2,y = 3,z = 5
x + y * z // Equals 17

let a1 = 3,b1 = 0.1415927
let pi1 = Double(a1) + b1 // 數值型類型轉換

/* 1.4 控制流程 */
let temperature = 100
if temperature >= 100 {
    print("The water is boiling.")
}else if temperature < 0 {
    print("The water is cold.")
}else{
    print("The water is not boiling.")
}

let numberOfWheels = 2
switch numberOfWheels{
case 1:
    print("Unicycle")
case 2:
    print("Bicycle")
default:
    print("That's a lot of wheels!")
}

let character = "z"
switch character{
case "a","e","i","o","u":
    print("This character is a vowel.")
default:
    print("This character is a consonat.")
}
let distance = 100
switch distance {
case 0...9:
    print("Your destination is close.")
case 10...99:
    print("Your destination is a medium distance from here.")
default:
    print("Are you sure you want to travel this far?")
}

/* 2.1字符串 */
let greeting = "Hello \"world\""
var myString = ""
if myString.isEmpty {
    print("The string is empty")
}
// 串聯和插值
myString = greeting + "yes"
let age1 = 30
let name1 = "Rick"
print("\(name1) is \(age1+5) years old")
// 字符串相等
if myString != greeting {
    print("The are not the same")
}
if greeting.contains("Hello") {
    print("Making an introduction")
}
print("the greeting len=\(greeting.count)")

/* 2.2函數 */
func displayPi(){
    print("3.1415927")
}
displayPi()
func triple(value: Int){
    let result = value * 3
    print("If you multiple \(value) by 3,you'll get \(result).")
}
// 自變量標籤，可省略參數標籤
triple(value: 20)
func triple2(_ value: Int){
    triple(value: value)
}
triple2(10)
// 默認參數值和返回多個值
func multiple(_ firstNumber: Int, secondNumber: Int = 10) -> (a: Int,b: Int){
    return (firstNumber * secondNumber , secondNumber)
}
var multipleResult = multiple(2)
print("Return=\(multipleResult) a=\(multipleResult.a) b=\(multipleResult.b)")

/* 2.3結構 */
struct Car{
    var make: String
    var year: Int = 0
    func startEngine() {}
    func drive() {}
}

var firstCar = Car(make: "Ford", year: 2013)
firstCar.startEngine()
firstCar.drive()
//構造器
var stringInit = String.init() // ""
var integerInit = Int.init() // 0
struct Temperature{
    var celsius: Double
    init(celsius: Double){
        self.celsius = celsius
    }
    
    init(fahrenheit: Double){
        self.celsius = (fahrenheit - 32) / 1.8
    }
}
var boiling = Temperature(fahrenheit: 212.0)
//計算屬性
struct Temperature2{
    var celsius: Double
    var fahrenheit: Double{
        return celsius * 1.8 + 32
    }
}
//屬性觀察器
struct StepCounter{
    var totalSteps: Int = 0 {
        willSet{
            print("About to set totalSteps to \(newValue)")
        }
        didSet{
            if totalSteps > oldValue{
                print("Added \(totalSteps - oldValue)")
            }
        }
    }
}
var stepCounter = StepCounter()
stepCounter.totalSteps = 40
stepCounter.totalSteps = 100
//拷貝
var t1 = Temperature2(celsius: 2.0)
var t2 = t1
t2.celsius = 10.0 // 拷貝結構體，所以不會影響原結構體的值
print(t1.celsius)

/* 2.4類與繼承 */
class Scientist{
    func doSomeThing() {
    }
}
class Geologist: Scientist{
    override func doSomeThing() {
    }
}

/* 2.5集合 */
// 數組
var names: [String] = ["Anne","Gray"]
var numbers = [1, -3, 24, 114]
if numbers.contains(24){
    print("There is a 24")
}
numbers[1] = 23
numbers.append(2) // 追加
numbers+=[1,3] // 一次追加多個元素
numbers.insert(31, at: 0)
numbers.remove(at: 0)
let array1 = [1,2,3]
let array2 = [4,5,6]
let arrayAll = [array1,array2] // [[1,2,3],[4,5,6]] // 二維數組
//字典
var myDictionary = [String:Int]()
var myDictionary2 = Dictionary<String,Int>()
myDictionary["Oli"] = 399 //添加
if let oldValue = myDictionary.updateValue(200, forKey: "Oli") {//更新
    print("Richard's old value was \(oldValue)")
}
var scores = ["Richard": 500, "Luke": 100] //訪問字典
let players = Array(scores.keys) // ["Richard", "Luke"]
let points = Array(scores.values)// [500, 100]
if let myScore = scores["Luke"] {
    print(myScore)
}else{
    print("Not find")
}

/* 2.6循環 */
// for/for-in
for index in 1..<5 {
    print("This is number\(index)")
}
let names2 = ["Joseph", "Cathy", "Winston"]
for item in names2 {
    print("Hello \(item)")
}
let vehicles = ["unicycle": 1, "bicycle":2]
for (key,value) in vehicles {
    print("A \(key) has \(value) wheels")
}
// while
var numberOfLives = 3
var stillAlive = true
while stillAlive {
    numberOfLives -= 1
    if numberOfLives == 0{
        break
    }
}

更新記錄

2019.08.23 初稿
2020.03.07 完善，增加目錄和更多的註釋

Swift5入門 - 基礎語法都給你總結好了 - 花10分鐘瞭解一下？

文章目錄

Swift語言基礎

1.1 Swift 和 Playground簡介

1.2 常量、變量和數據類型

數據類型

類型安全和類型推斷

1.3 運算符

1.4 控制流程

1.5 循環

for

for-in

while

1.6 集合

數組

字典

1.7 字符串

1.8 函數

1.9 枚舉

1.10 類

構造函數和析構

屬性和方法

繼承

計算屬性

屬性觀察器

1.11 結構體

定義

拷貝

1.12 協議（接口）

1.13 高級

可選鏈和類型轉換

閉包

泛型

完整的Playground項目

更新記錄