下面介紹2種swift的字符串截取方法,實(shí)際上用到了substringFromIndex, substringToIndex, substringWithRange

1. 將String轉(zhuǎn)化為NSString再截取,代碼如下：

var s="1234567890"

var ns1=(s as NSString).substringFromIndex(5)
var ns2=(s as NSString).substringToIndex(4)

var ns3=(s as NSString).substringWithRange(NSMakeRange(4, 1))

println(ns1)//67890
println(ns2)//1234
println(ns3)//5

2. 直接調(diào)用String的對應(yīng)方法(推薦使用該方法),由于String對應(yīng)的方法參數(shù)是String.Index類型而非Int類型,所以我們首先要?jiǎng)?chuàng)建String.Index類型參數(shù)值,代碼如下：

// var s="1234567890"

// let index = advance(s.startIndex, 5)  swift 1.x
//let index2 = advance(s.endIndex, -6); swift 1.x


var s="1234567890"

let index = s.startIndex.advancedBy(5) //swift 2.0+
let index2 = s.endIndex.advancedBy(-6) //swift 2.0+
var range = Range<String.Index>(start: index2,end: index)

var s1:String=s.substringFromIndex(index)
var s2:String=s.substringToIndex(index2)
var s3=s.substringWithRange(range)

print(s1)//67890
print(s2)//1234
print(s3)//5

 // 擴(kuò)展String

extension String {
    subscript (r: Range<Int>) -> String {
        get {
            let startIndex = self.startIndex.advancedBy(r.startIndex)
            let endIndex = self.startIndex.advancedBy(r.endIndex)

            return self[Range(start: startIndex, end: endIndex)]
        }
    }
}

var s4 = s[2...4]
print(s4);//345

通過String定義可以看出屬性Index是個(gè)結(jié)構(gòu)體,具體代碼如下：

extension String : CollectionType {
    struct Index : BidirectionalIndexType, Comparable, Reflectable {
        func successor() -> String.Index
        func predecessor() -> String.Index
        func getMirror() -> MirrorType
    }
    var startIndex: String.Index { get }
    var endIndex: String.Index { get }
    subscript (i: String.Index) -> Character { get }
    func generate() -> IndexingGenerator<String>
}

最后，有網(wǎng)友回復(fù)加一個(gè)set方法，感覺更完美，就都寫到這里:

set {
    let startIndex = self.startIndex.advancedBy(range.startIndex)
    let endIndex = self.startIndex.advancedBy(range.endIndex)
    let strRange = Range(startIndex..<endIndex)
    self.replaceRange(strRange, with: newValue)
}

**轉(zhuǎn)自: **

• swift中字符串截取方法(substring）