• iOSswift基础篇1


    一.swift是啥?答:百度。

    二.swift基础知识。

    1.输出函数:print

    print("Hello, world!")

    2.简单数据类型

     变量声明:var

      常量声明:let   

        var myVariable = 42
        myVariable = 50
        let myConstant = 42

    如果没有变量或者常量的类型(如下1、2行),定义的变量或者常量的类型是在第一次赋值时自动判定的。

    如果声明了类型(如下第3行),则必须赋值指定类型。

        let implicitInteger = 70
        let implicitDouble = 70.0
        let explicitDouble: Double = 70

    变量转换:

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

    字符串拼接

    字符串插入变量方法:\()

    将变量放入括号里面就ok了

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

    数组和字典:

    数组和字典对象都放在 [] 里面,用 ","分隔,并且最后一个对象后面可以加 逗号。

    创建有对象的字典和数组:

    1     var shoppingList = ["catfish", "water", "tulips", "blue paint"]
    2     shoppingList[1] = "bottle of water"
    3      
    4     var occupations = [
    5         "Malcolm": "Captain",
    6         "Kaylee": "Mechanic",
    7     ]
    8     occupations["Jayne"] = "Public Relations"

    创建空数组和字典:

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

    或者

    1     shoppingList = []
    2     occupations = [:]

    3.控制流(Control Flow)

    条件控制:if 和 switch

    循环控制:for-in,for,while 和 repeat-while

    用于条件判断的语句的圆括号是可选的。

    for-in:

     1     let individualScores = [75, 43, 103, 87, 12]
     2     var teamScore = 0
     3     for score in individualScores {
     4         if score > 50 {
     5             teamScore += 3
     6         } else {
     7             teamScore += 1
     8         }
     9     }
    10     print(teamScore)

    if:

    1     var optionalString: String? = "Hello"
    2     print(optionalString == nil)
    3      
    4     var optionalName: String? = "John Appleseed"
    5     var greeting = "Hello!"
    6     if let name = optionalName {
    7         greeting = "Hello, \(name)"
    8     }

    类型后面加“?”表示 可选类型(optional value)。

    if 和 let 一起使用判断值是否为nil,如果是nil,那么就会跳过这个模块。
    使用 if let 可以操作可选类型。

    ?,??:

    ?? 后面是 默认值

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

    使用  ?? 也可以操作可选类型。如果 可选类型值为nil 那么就使用 ?? 后面的默认值。

    switch:

    switch 支持多种类型的数据类型和比较运算。 不仅仅数值类型和相等判断。

     1     let vegetable = "red pepper"
     2     switch vegetable {
     3     case "celery":
     4         print("Add some raisins and make ants on a log.")
     5     case "cucumber", "watercress":
     6         print("That would make a good tea sandwich.")
     7     case let x where x.hasSuffix("pepper"):
     8         print("Is it a spicy \(x)?")
     9     default:
    10         print("Everything tastes good in soup.")
    11     }

    程序执行完 switch 的某个 case 后,会跳出switch,无需添加 break。

    for-in:

    for-in 遍历字典:

     1     let interestingNumbers = [
     2         "Prime": [2, 3, 5, 7, 11, 13],
     3         "Fibonacci": [1, 1, 2, 3, 5, 8],
     4         "Square": [1, 4, 9, 16, 25],
     5     ]
     6     var largest = 0
     7     for (kind, numbers) in interestingNumbers {
     8         for number in numbers {
     9             if number > largest {
    10                 largest = number
    11             }
    12         }
    13     }
    14     print(largest)

    while 和 repeat-while:

     1     var n = 2
     2     while n < 100 {
     3         n *= 2
     4     }
     5     print(n)
     6      
     7     var m = 2
     8     repeat {
     9         m *= 2
    10     } while m < 100
    11     print(m)

    ..< 和 ... 

    循环起止边界判断,使用 ..< 是包含最小值而不包含最大值。使用 ... 是最小值和最大值都包含。

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

    学习资源来自swift官方文档: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/GuidedTour.html#//apple_ref/doc/uid/TP40014097-CH2-ID1

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  • 原文地址:https://www.cnblogs.com/mengdongsky/p/6907602.html
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