ARRAYS,DICTIONARIES,LOOPS,SWITCH CASE
最后更新于：2022-04-01 04:44:25
## ARRAYS,DICTIONARIES,LOOPS,SWITCH CASE
* 通过类型注释（Type annotaions）可以申明数组内容的类型：
~~~
var songs: [String] = ["Shake it Off", "You Belong with Me", "Back to December", 3]
//以上会报错，因为数组内有非 String 类型的”3”在内。
~~~
* 以下代码仅仅是声明了一个将要被分配包含String对象数组的变量：
~~~
var array:[String]
//没有真正创建数组对象
var array: [String] = []
//这时才是创建了数组对象
var array = [String] ()
//效果同上，语法更为简洁。
~~~
* 数组可以直接使用”+”运算符结合：
~~~
var songs = ["Shake it Off", "You Belong with Me", "Love Story"]
var songs2 = ["Today was a Fairytale", "White Horse", "Fifteen"]
var both = songs + songs2
both += [“Everything”]
//可以增加并赋值
~~~
* 创建一个 Disctionary：
~~~
var person = [
"first": "Taylor",
"middle": "Alison",
"last": "Swift",
"month": "December",
"website": "taylorswift.com"
]
~~~
* Swift 中，条件表达式不需要括号：
~~~
if person == "hater" {
action = "hate"
} else if person == "player" {
action = "play"
} else {
action = "cruise"
}
~~~
* `在 Swift 2.0中，println() 改为 print()`
* Swift 的 for 循环语法：
~~~
// closed range operator
for i in 1...10{
println("\(i) x 10 is \(i * 10)")
}
/*
以上结果相当于：
println("1 x 10 is \(1 * 10)")
println("2 x 10 is \(2 * 10)")
println("3 x 10 is \(3 * 10)")
println("4 x 10 is \(4 * 10)")
println("5 x 10 is \(5 * 10)")
println("6 x 10 is \(6 * 10)")
println("7 x 10 is \(7 * 10)")
println("8 x 10 is \(8 * 10)")
println("9 x 10 is \(9 * 10)")
println("10 x 10 is \(10 * 10)")
*/
~~~
* 不需要「循环数」时也可以用下划线代替：
~~~
for _ in 1 ... 5 {
str += " fake"
}
~~~
* half open range operator(半开区间运算符):“..<"，例如 ..<5 将会循环四次，count 将会是 1,2,3,4。”..<“ 可以方便于遍历数组（数组的 index 从0算起）：
~~~
for i in 0 ..< count(people) {
println("\(people[i]) gonna \(actions[i])")
}
~~~
* 遍历数组的语法：
~~~
...
for song in songs {
println("My favorite song is \(song)")
}
//通过 index 同时遍历俩数组：
var people = ["players", "haters", "heart-breakers", "fakers"]
var actions = ["play", "hate", "break", "fake"]
for i in 0 ... 3 {
println("\(people[i]) gonna \(actions[i])")
}
~~~
* `获取数组内的对象数量的方法在 Swift 1.2中是 count(array)，在 Swift 2.0中是 array.count。`
* loop 中的 continue 语法 将会终止当前的迭代回到 loop 的开头继续迭代。
* switch/case 语法可以简化较多的 if/else if 语法，Swift 要求 switch 条件变量所有可能的情况都得涵盖（ cases should exhustive），否则 Xcode 可能无法构建应用，default 可以避免该问题。
* 可以在 switch/case 中使用 “…”(half open range operator) 将变量可能的范围作为一个 case：
~~~
let studioAlbums = 5
switch studioAlbums {
case 0...1:
println("You're just starting out")
case 2...3:
println("You're a rising star")
case 4...5:
println("You're world famous!")
default:
println("Have you done something new?")
}
~~~
* `Swift 2.0 方法调用和1.2稍有不同，需要写明参数名，目的是提高代码可读性：`
~~~
func printAlbumRelease(name: String, year: Int) {
println("\(name) was released in \(year)")
}
printAlbumRelease("Fearless", year: 2008)
printAlbumRelease("Speak Now", year: 2010)
printAlbumRelease("Red", year: 2012)
~~~
* “->"符号为方法声明返回值：
~~~
func albumsIsTaylor(name: String) -> Bool
~~~