学无止境 keep moving
定义基本数据格式
let myKobe = 24
let myData : Double = 23.0 //指定类型定义
let binaryInteger = 0b10001 //二进制数
let octalInteger = 0o21 //八进制数
let hexadecimalInteger = 0x11 //十六进制
let scienceNumber = 1.234e3 //科学计数
变量定义
var myVariable = 23
类型转换
var leb = "23"
let str = "\(leb)"
let str1 = String(str)
let str2 = Int(str)
let str3 = Int(leb)
let str4 = Double(str1!)
数组的定义方式
let list1 = ["bonjour","23","3"]
var list2 : [String] = ["bonjour","23","3"]
let list3 : [Any] = ["bonjour","33","4"]
let list4 : NSArray = ["bonjour","23","1"]
let list5 :NSMutableArray = ["bonjour","423","4"]
//remove
list2.removeAll() //var 可以
list2 = [] //var 可以
list5.removeAllObjects() // var 和 let 都可以
tempArray[1...4] = ["沙扬娜拉","apple"] // 将数组4...6 的范围用指定的数组取代
list5.add("34")
list5.insert("Maple Syrup", at: 0)
list5.removeObject(at: 1)
字典的定义方式
let dict1 : [String : Int] = [:]
let dict2 = [String:Int]()
let dict3 : NSDictionary = NSDictionary()
let dict4 : NSMutableDictionary = NSMutableDictionary()
获取数据类型的最大和最小值
let minValue = UInt8.min
let maxValue = UInt8.max
给数据类型设置别名
typealias code = Int32
var tel : code = 35232
元祖
1.定义
//第一种定义方式
let http404Error = (404,"Not Found")
let codeNum = http404Error.0
let error = http404Error.1
//第二种定义方式
let http404Error = (code:404, error:"Not Found")
let codeNum = http404Error.code
let error = http404Error.error
//第三种定义方法
let http404Error:(code:Int,error:String) = (404,"Not Found")
let code = http404Error.code
let error = http404Error.1
//第四种定义方法
let http404Error:(code:Int,error:String) = (code:404,error:"Not Found")
let code = http404Error.code
let error = http404Error.error
//第五种定义方式
var http404Error :(code:Int , error : String) = (_ :404, _ : "Not Found")
//第四种定义的时候,等号坐标和右边的元素名称必须对应,不然系统会报错,建议不使用这种方式定义
2.分解变量
let (statusCode, _) = http404Error //缺省不需要的值
let (statusCode, statusMessage) = http404Error
- 赋值
var http404Error : (code:Int,error:String)
http404Error = (code:404,error:"Not Found")//完整
http404Error = (404, "Not Found") //全部名称缺省
http404Error = (code : 404, "Not Found") //部分缺省
http404Error = (_ :404 , "Not Found")
字符串
let string = "Hello." + "World" //so Fantice let
var name = "natali"
name.append("你好") // var
var anotherEmptyString = String()
//判断字符串是否为空
var emptyString = String()
if emptyString.isEmpty {
print("Nothing to see here")
}
//获取字符串中每个字符
for character in "Dog!🐶".characters {
print(character)
}
let nike = "Nothing is impossiable"
for indedx in nike.characters.indices {
print("\(nike[indedx])", separator: "1", terminator: "")
}
//定义字符
let exclamationMark :(Character) = "!"
//定义字符数组
let carcharacters : [Character] = ["C", "a", "t", "!", "🐱"]
//定义数组转字符串
let catString = String(carcharacters)
//Unicode编码
let percomosed:Character = "\u{D55C}" //🇰🇷
let regionalIndicatorForUS: Character = "\u{1F1FA}\u{1F1F8}" //🇺🇸
var nickname = "🐶东西add"
print(nickname.characters.count) // 6 都是一个字符
//截取字符串
let greeting = "bonjunor"
//截取单个
greeting[greeting.startIndex]
//截取一段
greeting[greeting.index(greeting.startIndex, offsetBy: 2)..<greeting.index(greeting.endIndex, offsetBy: -3)]
//在指定位置插入字符串
var welcome = "welcome"
welcome.insert("!", at: welcome.endIndex)
welcome.insert(contentsOf: "here".characters, at: welcome.index(before: welcome.endIndex))
//移除字符串
// welcome.remove(at: welcome.index(before: welcome.endIndex))
let range = welcome.index(welcome.endIndex, offsetBy: -6)..<welcome.endIndex
welcome.removeSubrange(range)
// 前缀和后缀
let scene = "Capulet`s mansion"
if scene.hasSuffix("Capulet`s mansion") {
} //hasPrefix
//获取对应的编码数据
for codeunit in "🐶a店待你".utf16 {
print("\(codeunit)")
}
深入学习
拓展
extension Int {
func description() -> String {
return "这是一个Int类型的数\(self)"
}
}
print(2.description())
这是一个Int类型的数2
1.定义一个协议
protocol NumberProtocl {
func description() -> String
}
2.拓展实现协议
extension Int : NumberProtocl {
func description() -> String {
return "This is a Int Number\(self)"
}
}
extension Double : NumberProtocl {
func description() -> String {
return "This is a Double Number \(self)"
}
}
3.定义一个协议类型
var a:NumberProtocl = 3
print(a.description())
a = 3.4
print(a.description())
运行
我是一个Int类型的数字3
我是一个Double类型的数字3.4
通过这种方法,我们可以给同一个变量,赋值不同类型的值了,其实这个符合swift的语法要求,只是我们利用它的灵活性,达到了我们的目的
给系统类添加拓展
给Int 类型和 Double类型增加一个方法,判断它的数据类型
//定义一个协议
protocol whichTypeProtocol {
}
//拓展实现协议
extension Int : whichTypeProtocol{
}
extension Double : whichTypeProtocol {
}
//给协议拓展方法
extension whichTypeProtocol {
func description() -> String {
if self is Int {
return " This is Int \(self)"
}
if self is Double {
return "This is Double \(self)"
}
return "Nothing"
}
}
print(3.44.description())
print(3.description())
Self的好处
专门用于不确定数据类型的
需求:给所有数字类型,扩展一个平方的函数,返回自己的操作
//定义一个协议
protocol getSpuareValue {
}
//拓展实现协议
extension Int : getSpuareValue {
}
extension Double : getSpuareValue {
}
extension getSpuareValue {
//我们不确定返回的self 是什么类型
func spuareValue() -> Self {
if self is Int {
let n = self as! Int
return n * n as! Self
}
if self is Double {
let m = self as! Int
return m * m as! Self
}
return 0 as! Self
}
}
print(3.44.squareValue())
print(3.squareValue())
11.8336
9
结论
Self很强大
需要注意的地方
1.如果指出变量的类型,赋值的值必须是和他类型相同的值,不然编译不通过
var num:Int = 43.0//(编译错误)
2.浮点数类型推断出来的默认为Double类型
let name = 30.0 // Double
3.Float 类型的值 赋值给Double类型也必须转换
let name:Float = 30.0
let explicitDouble: Double = Double(name)
4.数字之间的转换结果为非可选值,数字转字符串也是非可选值,但是字符串转数字就是可选值(因为它有可能转换失败)
let str = "\(num1)"
let str1 = String(num1)
let num2 = Int(num1)
let num3 = Int(str1)
let num4 = Double(str1)
输出结果:
30.0
30
nil
Optional(30.0)
注意:
字符串33.0 转Int 类型只会是nil 不会是33 因为字符串33.0 不是Int类型转换失败,但是浮点数33.0 可以转换为33
5.不能推断出下面的类型
let list1 = ["你好","2","3",3] // 不能这样写,swift推断不出来
你应该:
let list1 = ["你好","2","3",3] as [Any]
let list1:[Any] = ["你好","2","3",3]
let list1:NSArray = ["你好","2","3",3]
let list1:NSMutableArray = ["你好","2","3",3]
6.使用Dictionary定义字典必须指定数据类型
let dic5:Dictionary = [:] // 错误
let dic5:Dictionary = [String:Int]() // 正确
Array 和NSArray,NSMutableArray的区别
1.测试类型
var list1:Array = ["你好","2","3","4"]
let list2 = list1
list1[1] = "哈哈"
print(list1)
print(list2)
运行结果:
["你好", "哈哈", "3", "4"]
["你好", "2", "3", "4"]
var list1:NSMutableArray = ["你好","2","3","4"]
let list2 = list1
list1[1]="哈哈"
print(list1)
print(list2)
运行结果:
("你好", "哈哈", "3", "4")
("你好", "哈哈", "3", "4")
结论:
Array 为值类型,NSArray,NSMutableArray为引用类型
2.测试内存占用
func add(){
var array: [Any] = [3]
for _ in 0...10000000{
array.append(3)
}
}
执行代码前 3.5M 执行代码后 3.8 M 内存占用最高 308.6M
func add(){
let array: NSMutableArray = NSMutableArray()
for i in 0...10000000{
array.add(3)
if i == 10000000{
}
}
}
执行代码前3.5 M ,代码执行完毕后 17.3M,内存占用最高为 422.3
3.我们使用Array 放对象
func add(){
var array: [Any] = []
for i in 0...10000{
array.append([UILabel()])
}
运行前 3.5 运行后10.5 最高占内存 21.5，发现内存没有释放完毕
尝试修改代码如下:
autoreleasepool {
var array: [Any] = []
for i in 0...10000{
array.append([UILabel()])
}
}
运行结果依旧
结论:
Swift 中新增的Array 存放非对象类型,内存清理的更及时,更彻底!
4.数据的上溢或者下溢系统都会报错
Int8.min - 1
Int8.max + 1
arithmetic operation '127 + 1' (on type 'Int8') results in an overflow
error: arithmetic operation '-128 - 1' (on type 'Int8') results in an overflow
原文出处
作者：酷走天涯
链接：http://www.jianshu.com/p/a53429e4e2f3
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