随着swift语言的不断发展，越来越来趋于稳定化。现在也有很多公司使用swift来开发新的App，那么不会swift开发的iOS开发者在竞争中还是很弱势的，所有学习swift是大势所趋。本系列文章根据以往的学习积累和项目经验，从基础到原理详细说说swift的这点事儿，不喜勿喷，交流指正请加微信。

WeChatdfdb8bfa7f0a84545d010ef18af70a98.png

一. if else

        let age = 4
        if age >= 22 {
            print("Get married")
        } else if age >= 18 {
            print("Being a adult")
        } else if age >= 7 {
            print("Go to school")
        } else {
            print("Just a child")
        }

注意点：

if后面的条件可以省略小括号
条件后面的大括号不可以省略
if后面的条件只能是Bool类型

二. while

var num = 5
        while num > 0 {
            print("num is \(num)")
            num -= 1
        } // 打印了5次

repeat while

var num = -1
        repeat {
            print("num is \(num)")
        } while num > 0 // 打印了1次

注意点：

repeat-while相当于C语言中的do-while 这里不用num--，是因为 从Swift3开始，去除了自增（++）、自减（--）运算符

三. for 循环

// 闭区间运算符：a...b， a <= 取值 <= b
        let names = ["Anna", "Alex", "Brian", "Jack"]
        for i in 0...3 {
            print(names[I])
        }
        //输出： Anna Alex Brian Jack

        
        let range = 1...3
        for i in range {
            print(names[I])
            
        }
        //输出： Alex Brian Jack

        
        let a = 1
        var b = 2
        for i in a...b{
            print(names[I])
        }
        //输出： Alex Brian


        // i默认是let，有需要时可以声明为var
        for var i in 1...3 {
            i += 5
            print(i)
        }
        //输出： 6 7 8

        
        for _ in 1...3 {
            print("for")
        }
        // 打印了3次

        
        // 半开区间运算符：a..<b， a <= 取值 < b
        for i in 1..<5 {
            print(i)
        }
        //输入： 1 2 3 4

for – 区间运算符用在数组上

        let names = ["Anna", "Alex", "Brian", "Jack"]
        for name in names[0...3] {
            print(name)
        }
        //输出： Anna Alex Brian Jack

        // 单侧区间：让区间朝一个方向尽可能的远
        for name in names[2...] {
            print(name)
        }
        //输出： Brian Jack
        
        for name in names[...2] {
            print(name)
        }
        //输出： Anna Alex Brian

        for name in names[..<2] {
            print(name)
        }
        //输出： Anna Alex

        let range = ...5
        range.contains(7) // false
        range.contains(4) // true
        range.contains(-3) // true

带间隔的区间值

 let hours = 11
        let hourInterval = 2
        // tickMark的取值：从4开始，累加2，不超过11
        for tickMark in stride(from: 4, through: hours, by: hourInterval) {
            print(tickMark)
        } // 4 6 8 10

四：switch 循环

        var number = 1
        switch number {
        case 1:
            print("number is 1")
            break
        case 2:
            print("number is 2")
            break
        case 3:
            print("number is 2")
            break
        default:
            print("number is 2")
            break
        }

注意

case、default后面不能写大括号{}

        var number = 1
        switch number {
        case 1:
            print("number is 1")
        case 2:
            print("number is 2")
        case 3:
            print("number is 2")
        default:
            print("number is 2")
        }

注意

默认可以不写break，并不会贯穿到后面的条件

fallthrough ，使用fallthrough可以实现贯穿效果

        var number = 1
        switch number {
        case 1:
            print("number is 1")
            fallthrough
        case 2:
            print("number is 2")
        default:
            print("number is other")
            break
        // 输出：number is 1 number is 2

switch必须要保证能处理所有情况

企业微信截图_712e7f51-6001-41ac-8dbe-64671badf5db.png

case、default后面至少要有一条语句 如果不想做任何事，加个break即可

var number = 1
        switch number {
        case 1:
            print("number is 1")
        case 2:
            print("number is 2")
        default:
            break
        }

switch注意点 如果能保证已处理所有情况，也可以不必使用default

        enum Answer {
            case right, wrong
        }
        let answer = Answer.right
        switch answer {
        case Answer.right:
            print("right")
        case Answer.wrong:
            print("wrong")
        }
    
        // 由于已确定answer是Ansewer类型，因此可以省略Answer
        switch answer {
        case .right:
            print("right")
        case .wrong:
            print("wrong")
        }

复合条件

// switch也支持Character、String类型
        let string = "Jack"
        switch string {
        case "Jack":
            fallthrough
        case "Rose":
            print("Right person")
        default:
            break
        }
        // Right person

        let character: Character = "a"
        switch character {
        case "a", "A":
            print("The letter A")
        default:
            print("Not the letter A")
            
        }
        // The letter A

        switch string {
        case "Jack", "Rose":
            print("Right person")
        default:
            break
        }
        // Right person

区间匹配

        let count = 62
        switch count {
        case 1..<5:
            print("none")
        case 5..<12:
            print("a few")
        case 12..<100:
            print("dozens of")
        case 100..<1000:
            print("hundreds of")
        default:
            print("many")
        //输出: dozens of

元组匹配

let point = (1, 1)
        switch point {
        case (0, 0):
            print("the origin")
        case (_, 0):
            print("on the x-axis")
        case (0, _):
            print("on the y-axis")
        case (-2...2, -2...2):
            print("inside the box")
        default:
            print("outside of the box")
            
        }
        //输出： inside the box

可以使用下划线 _ 忽略某个值

值绑定

        let point = (2, 0)
        switch point {
            case (let x, 0):
            print("on the x-axis with an x value of \(x)")
        case (0, let y):
            print("on the y-axis with a y value of \(y)")
        case let (x, y):
            print("somewhere else at (\(x), \(y))")
        }
        // on the x-axis with an x value of 2

where 语句

        let point = (1, -1)
        switch point {
        case let (x, y)where x == y:
            print("on the line x == y")
        case let (x, y) where x == -y:
            print("on the line x == -y")
        case let (x, y):
            print("(\(x), \(y)) is just some arbitrary point") }
 // on the line x == -y

// 将所有正数加起来
        var numbers = [10, 20, -10, -20, 30, -30]
        var sum = 0
        for num in numbers where num > 0 { // 使用where来过滤num
            sum += num
        }
        print(sum) // 60

标签语句

        outer: for i in 1...4 {
            for k in 1...4 {
                if k == 3 {
                    continue outer
                }
                if i == 3 {
                    break outer
                }
                print("i == \(i), k == \(k)") }
        }

关于swift的更多知识
请点击 swift文集