带有substringWithRange的Swift 2.0字符串

Question

我想从String中获取第一个char。 它应该很容易，但我不能在Swift 2.0中使用（使用Xcode beta 6）。

在Swift编程语言中获取字符串的第n个字符

我也试过那种方法。 它使用扩展但我无法使用该方法检索。 我可以知道该怎么办吗？

Answer 1

没有强制转换为NSString的两种解决方案

let string = "Hello"
let firstChar1 = string.substringToIndex(string.startIndex.successor())

let firstChar2 = string.characters.first

Swift 2更新：

由于斯威夫特2返回Character ，而不是String新的String必须创建。

let firstChar2 = String(string.characters.first!)

Swift 3更新：

successor()已被index(after:..)替换index(after:..)

let firstChar1 = string.substring(to:string.index(after: string.startIndex))

Answer 2

试试这个，

let str = "hogehoge"
let text = (str as NSString).substringFromIndex(1) // "ogehoge"

Answer 3

对于它的价值（以及搜索和查找此主题的人），不将String转换为NSString，您需要使用Swift 2.1执行以下操作：

let myString = "Example String"
let mySubString = myString.substringWithRange(Range<String.Index>(start: myString.startIndex.advanceBy(0), end: myString.startIndex.advanceBy(4)))

print(mySubString) //'Exam'

这将打印出“考试”。 必须说它比Obj-C更冗长。 那是在说些什么...... ;-)但它完成了工作而没有投射到NSString。

Answer 4

试试这个

let myString = "My String" as NSString
myString.substringWithRange(NSRange(location: 0, length: 3))

Answer 5

在Swift 2中， String不是任何东西的集合。 根据文件：

/// `String` is not itself a collection of anything.  Instead, it has
/// properties that present the string's contents as meaningful
/// collections:
///
///   - `characters`: a collection of `Character` ([extended grapheme
///     cluster](http://www.unicode.org/glossary/#extended_grapheme_cluster))
///     elements, a unit of text that is meaningful to most humans.
///
///   - `unicodeScalars`: a collection of `UnicodeScalar` ([Unicode
///     scalar
///     values](http://www.unicode.org/glossary/#unicode_scalar_value))
///     the 21-bit codes that are the basic unit of Unicode.  These
///     values are equivalent to UTF-32 code units.
///
///   - `utf16`: a collection of `UTF16.CodeUnit`, the 16-bit
///     elements of the string's UTF-16 encoding.
///
///   - `utf8`: a collection of `UTF8.CodeUnit`, the 8-bit
///     elements of the string's UTF-8 encoding.

假设你想找到第二个字符，

var str = "Hello, playground"
let chars = str.characters
let n = 2
let c = str.characters[str.characters.startIndex.advancedBy(n)]

Answer 6

var mySuperCoolString = "Hello, World!!!!!!!!1!!";    
println(mySuperCoolString.substringWithRange(Range<String.Index>(start: advance(mySuperCoolString.startIndex, 0), end: advance(mySuperCoolString.startIndex, 1))));

这应该打印出H

Answer 7

Swift 2.2和Swift 3.0

let string = "12134"
string.substringWithRange(string.startIndex..<string.startIndex.advancedBy(2))