我怎样才能得到字符串的第n个字符?我尝试了括号([])访问器,没有运气。

var string = "Hello, world!"

var firstChar = string[0] // Throws error

错误:'下标'是不可用的:不能下标String与Int,请参阅文档注释讨论


当前回答

我的解决方法很简单:

斯威夫特4.1:

let myString = "Test string"
let index = 0
let firstCharacter = myString[String.Index(encodedOffset: index)]

斯威夫特5.1:

let firstCharacter = myString[String.Index.init(utf16Offset: index, in: myString)]

其他回答

如果你看到不能下标一个类型为'String'的值…使用这个扩展:

斯威夫特3

extension String {
    subscript (i: Int) -> Character {
        return self[self.characters.index(self.startIndex, offsetBy: i)]
    }

    subscript (i: Int) -> String {
        return String(self[i] as Character)
    }

    subscript (r: Range<Int>) -> String {
        let start = index(startIndex, offsetBy: r.lowerBound)
        let end = index(startIndex, offsetBy: r.upperBound)
        return self[start..<end]
    }

    subscript (r: ClosedRange<Int>) -> String {
        let start = index(startIndex, offsetBy: r.lowerBound)
        let end = index(startIndex, offsetBy: r.upperBound)
        return self[start...end]
    }
}

斯威夫特2.3

extension String {
    subscript(integerIndex: Int) -> Character {
        let index = advance(startIndex, integerIndex)
        return self[index]
    }

    subscript(integerRange: Range<Int>) -> String {
        let start = advance(startIndex, integerRange.startIndex)
        let end = advance(startIndex, integerRange.endIndex)
        let range = start..<end
        return self[range]
    }
}

来源:http://oleb.net/blog/2014/07/swift-strings/

我也有同样的问题。简单地这样做:

var aString: String = "test"
var aChar:unichar = (aString as NSString).characterAtIndex(0)

你可以通过将字符串转换为数组,并通过下标获得特定的索引,如下所示

var str = "Hello"
let s = Array(str)[2]
print(s)

我是斯威夫特4号

let myString = "LOVE"

self.textField1.text = String(Array(myString)[0])
self.textField2.text = String(Array(myString)[1])
self.textField3.text = String(Array(myString)[2])
self.textField4.text = String(Array(myString)[3])

你可以使用SwiftString (https://github.com/amayne/SwiftString)来做这件事。

"Hello, world!"[0] // H
"Hello, world!"[0...4] // Hello

免责声明:我写了这个扩展