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swift学习笔记

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ZefengYu edited this page Dec 30, 2015 · 2 revisions

@(swift)[swift] #learn the swift

online compiler

  1. get the different of the heap and stack : (1). every class is in the heap
  2. option
  3. core os -> core service ->media -> cocoa touch
  4. framworks : Foundation and UIKit :Core Data,Map Kit,Core Motion
  5. 元组在临时组织值的时候很有用，但是并不适合创建复杂的数据结构，如果你的数据结构并不是临时使用，请使用类或结构体而不是元组。

(1). ！获取可选值的值，可选值的强制解析

let possibleNumber = "123"
let convertNumber = possibleNumber.toInt()
//假设convertedNumber是int可选值
println(convertedNumber)
//Optional(123)
println(convertedNumber!)
//123

(2). optional binding 可选绑定

let actualNumber = possibleNumber.toInt()
//actualNumber 只被用来转换结果

(3). 可选变量赋值为nil来表示它没有值，不用用于非可选的常量和变量。如果你的代码中有常量或者变量需要处理缺失的情况，请把他们声明成对应的可选类型。nil不是指针，是一个确定的值，用来表示缺失。任何类型的可选状态都可以被设置为nil。

var serverReponseCode:Int? = 404

(4). 隐式解析可选类型

把想要用作可选的类型的后面的问号(string ?)改成感叹号(string !)来声明一个可选隐式>解析类型。

  1. nil coalescing operator 空和运算符( a??b)

对可选类型a进行空判断，相当于a!=nil?a!:b

  1. 区间运算符 a...b 半区间运算符 a..<b
  2. 短路计算 short-circuit evaluation
  3. 逻辑运算符，通过括号来明确优先级，增加可读性
  4. 字符串和字符 String Character，快速的兼容Unicode的方式来处理代码中的文本信息。 (1).String Literals 字符串字面量
//空字符串字面量
var emprtyString = ""
//初始化String实例
var anotherEmptyString = String()

###swift 基本语法

//1.输出
print( "Hello, playground")

//2.常量与变量
var a="我是变量"
let b="我是常量"

//3.指明类型
let letInteger :int_fast32_t = 70;
let letDouble :Double = 70.0;
let letString :NSString = "HelloSwift"

//4.转换字符串：String()或\()
let myString = "myInt is "
let myInt = 94
let myString2 = myString + String(myInt)
let myString3="myInt is \(myInt)"

//5.数组创建与调用
var array = ["one", "two", "three", "four"]
var getTwo=array[1];

//6.数据字典创建与调用
var dictionary=["oneName":"I am one value","twoName":"I am two value"];
var getTowValue=dictionary["twoName"];

//7.for语句
for item in array
{
    var i=item;
}

//8.函数
func getUserName(loginName:String)->String
{
    return"Lily";
}
//9.枚举
enum Week {
    case 星期一
    case 星期二
    case 星期三
    case 星期四
    case 星期五
    case 星期六
    case 星期天
}

//10.Switch语句
var today="星期一"
switch today{
        case "星期一":
        print("今天是星期一");
        case "星期二":
        print("今天是星期二");
        default:
        print("不知道今天星期几");
}

//11.类
class Person :NSObject
{
    var userName:String;
    var userAge=0;
    override init()
    {
        userName="";
    }
}

PLAYGROUND 可视化 由 王巍 (@ONEVCAT) 发布于 2015/09/23

//冒泡排序算法
var arr = [14, 11, 20, 1, 3, 9, 4, 15, 6, 19,
    2, 8, 7, 17, 12, 5, 10, 13, 18, 16]

func plot<T>(title: String, array: [T]) {
    for value in array {
        XCPCaptureValue(title, value: value)
    }
}

plot("起始", array: arr)

func swap(inout x: Int, inout y: Int) {
    (x, y) = (y, x)
}

func bubbleSort<T: Comparable>(inout input: [T]) {
//T必须遵守Comparable协议，即可比性协议
    for var i = input.count; i > 1; i-- {
        var didSwap = false
        for var j = 0; j < i - 1; j++ {
            if input[j] > input[j + 1] {
                didSwap = true
                swap(&input[j], &input[j + 1])
            }
        }
        if !didSwap {
            break
        }
        plot("第 \(input.count - (i - 1)) 次迭代", array: input)
    }
    plot("结果", array: input)
}

bubbleSort(&arr)

Swift/iOS: How to use inout parameters in functions with AnyObject/Any or Pointers

func setValue<T>(inout object: T, key: String) {
    switch key {
    case "String":
        object = ("A String" as? T)!
    case "UIColor":
        object = (UIColor.whiteColor() as? T)!
    case "Bool":
        object = (true as? T)!
    default:
        print("Unhandled key: \(key)")
    }
}

var string: String = "Default String"
var color: UIColor = UIColor.blackColor()
var bool: Bool = false

setValue(&string, key: "String")
setValue(&color, key: "UIColor")
setValue(&bool, key: "Bool")
/*
	 	
If you are going to force-cast (and please don’t, there are better solutions), you can do value as! Thing rather than (value as? Thing)!. – Airspeed Velocity Apr 30 at 9:52
1	 	
This is what I was looking for! Thanks a lot! – Django Apr 30 at 9:54
  	 	
I was struggling with the same error message as the OP, so thank you for this answer! I still don't quite understand why we need to use a generic function if we're just trying to cast a subclass to its superclass, though. – Alexander Oct 1 at 19:59
*/

###swift's changes

//swift's changes
//old
var str = "12"
var val1 = str.toInt()
//new
var str = "12"
var intValue = Int(str)

###swift tips

  1. 与effective-c 2.0说法有出入，dan

虽然说使用 enumerateObjectsUsingBlock: 非常方便，但是其实从性能上来说这个方法并不理想 (这里有一篇四年前的星期五问答阐述了这个问题，而且一直以来情况都没什么变化)。另外这个方法要求作用在 NSArray 上，这显然已经不符合 Swift 的编码方式了。在 Swift 中，我们在遇到这样的需求的时候，有一个效率，安全性和可读性都很好的替代，那就是快速枚举某个数组的 数组 ENUMERATE

  1. control transfer statement
  • continue
  • break
  • fallthrough
  • return
  • throw

######continue(loop) "I am done with the current loop iteration" without leaving the loop altogether.

######break(switch,loop) ends excutions of an entire control flow statement immediately.

######labeled statement

labeled name: while condition{
	statement
}

######early exit guard You use a guard statement to require that condition must be true in order for the code after the guard statement to be executed. ######checking API availability

if #available(iOS9,*){
	
}else{

}
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