最近寫(xiě)基于Swift 4.0的項(xiàng)目澎蛛，每次用到String的時(shí)候就要去查詢半天啡彬，再與NSString對(duì)比压真，實(shí)在忍受不了查找了，就自己總結(jié)一下常用的用法吧车酣，正好也是第一次嘗試寫(xiě)文章曲稼，希望能每周堅(jiān)持寫(xiě)一篇總結(jié)。
廢話不多說(shuō)開(kāi)始總結(jié)：
1湖员、正常用法：
let greeting ="Welcome"
2贫悄、多行字符串文字Swift 4.0新的用法：
如果要使用換行符來(lái)使源代碼更容易閱讀，但是您不希望換行符成為字符串值的一部分娘摔，請(qǐng)?jiān)谶@些行的末尾寫(xiě)入反斜杠（\）
同時(shí)注意特殊符號(hào)的用法 \" , ' , \t , \0 , \n , \r , \\ 等等
let quotation = """
\"Hello this is Multiline \
String Literals
please input you name
"哈哈哈窄坦，是不是很爽"
what are you doing
"""
3、初始化空字符串
//初始化空字符串
var emptyString = ""
var otheremptyString = String()
//判斷是否是空字符串
if emptyString.isEmpty {
print("空字符串")
}
//賦值
otheremptyString = "Hello"
//count 統(tǒng)計(jì)長(zhǎng)度
print(otheremptyString.count)//此處輸出5
//以C語(yǔ)言的字符串初始化
let cStr = String(cString:...)
//以URL初始化
let urlStr = String(contentsOf: URL, encoding: String.Encoding)
//以File路徑初始化
let fileStr = String(contentsOfFile: String, encoding: String.Encoding)
//以Data類型初始化
let urlStr = String(data: Data, encoding: String.Encoding)
// 格式化初始字符串
let f = 123.4322
let fStr = String(format: "%.2f", f)
print("fStr = \(fStr)")
// 以subString 初始化字符串
let substr = String(Substring)
4凳寺、訪問(wèn)和修改字符串
let greeting = "Guten Tag!"
let start = greeting[greeting.startIndex]
print("start = \(start)")//start = G
let beforeEnd = greeting[greeting.index(before: greeting.endIndex)]
print("beforeEnd = \(beforeEnd)")//beforeEnd = !
let afterStart = greeting[greeting.index(after: greeting.startIndex)]
print("afterStart = \(afterStart)")//afterStart = u
let index = greeting.index(greeting.startIndex, offsetBy: 6)
print("index = \(index)")
let m = greeting[index]
print("m = \(m)")//m = T
//insert方法貌似已經(jīng)被去掉
let r = greeting.remove(at: index)
print("r = \(r)")//r = T
print("greeting = \(greeting)")//greeting = Guten ag!
let range = greeting.index(greeting.endIndex, offsetBy: -5)..<greeting.endIndex
greeting.removeSubrange(range)
print("greeting = \(greeting)") //greeting = Gute
5鸭津、拼接字符串 + 或 += 或 append
let k = emptyString + " dsjjdjsjd"
print(k)
otheremptyString += " Boy!"
print(otheremptyString)
let ex: Character = "!"
otheremptyString.append(ex)
print(otheremptyString)
6、比較或截取字符串
let quotation = "We're a lot alike, you and I."
let sameQuotation = "We're a lot alike, you and I."
if quotation == sameQuotation { // == 判斷是否相等 !=判斷不等
print("These two strings are considered equal")
}
let hasPreFixStr = "Welcome Hello World!"
if hasPreFixStr.hasPrefix("W") {
print("以W開(kāi)頭")
}
if hasPreFixStr.hasSuffix("!") {
print("以!結(jié)尾")
}
let dogStr = "Dog!!??"
for scalar in dogStr.unicodeScalars {
print("\(scalar) ")
}//UnicodeScalar, 可以直接打印unicode字符
let pre = hasPreFixStr.prefix(3)
let suf = hasPreFixStr.suffix(3)
let dropFirst = hasPreFixStr.dropFirst()
let dropLast = hasPreFixStr.dropLast()
//注意這些pre肠缨、suf逆趋、dropFirst、dropLast是SubSequence也就是Substring類型,要使用再轉(zhuǎn)換成String
let newStr = String(suf)
7晒奕、字符串按對(duì)應(yīng)的字符分割為數(shù)組
let line = "BLANCHE: I don't want realism. I want magic!"
print(line.split(separator: " "))
//["BLANCHE:", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]
print(line.split(separator: " ", maxSplits: 1))
//["BLANCHE:", " I don\'t want realism. I want magic!"]
print(line.split(separator: " ", omittingEmptySubsequences: false))
//["BLANCHE:", "", "", "I", "don\'t", "want", "realism.", "I", "want", "magic!"]
