我还没有弄清楚如何在Swift中获得字符串的子字符串:

var str = “Hello, playground”
func test(str: String) -> String {
 return str.substringWithRange( /* What goes here? */ )
}
test (str)

我不能在Swift中创建一个范围。自动完成在游乐场不是超级有用的-这是它的建议:

return str.substringWithRange(aRange: Range<String.Index>)

我在Swift标准参考库中没有找到任何有用的东西。下面是另一个大胆的猜测:

return str.substringWithRange(Range(0, 1))

这:

let r:Range<String.Index> = Range<String.Index>(start: 0, end: 2)
return str.substringWithRange(r)

我看到了其他答案(在Swift字符串中查找字符索引),似乎表明,由于字符串是NSString的桥类型,“旧”方法应该工作,但不清楚如何-例如,这也不工作(似乎不是有效的语法):

let x = str.substringWithRange(NSMakeRange(0, 3))

想法吗?


当前回答

如何在Swift 2.0中获取子字符串的示例代码

(i)起始索引的子字符串

输入:-

var str = "Swift is very powerful language!"
print(str)

str = str.substringToIndex(str.startIndex.advancedBy(5))
print(str)

输出:

Swift is very powerful language!
Swift

(ii)特定索引的子字符串

输入:-

var str = "Swift is very powerful language!"
print(str)

str = str.substringFromIndex(str.startIndex.advancedBy(6)).substringToIndex(str.startIndex.advancedBy(2))
print(str)

输出:

Swift is very powerful language!
is

希望对你有所帮助!

其他回答

首先创建范围,然后是子字符串。你可以使用fromIndex..<toIndex语法如下:

let range = fullString.startIndex..<fullString.startIndex.advancedBy(15) // 15 first characters of the string
let substring = fullString.substringWithRange(range)

简单的解决方案,很少的代码。

做一个扩展,包括基本的子字符串,几乎所有其他语言都有:

extension String {
    func subString(start: Int, end: Int) -> String {
        let startIndex = self.index(self.startIndex, offsetBy: start)
        let endIndex = self.index(startIndex, offsetBy: end)

        let finalString = self.substring(from: startIndex)
        return finalString.substring(to: endIndex)
    }
}

简单地用

someString.subString(start: 0, end: 6)

由于String是NSString的桥接类型,“旧的”方法应该可以工作,但不清楚如何工作-例如,这也不起作用(似乎不是有效的语法): let x = str.substringWithRange(NSMakeRange(0,3))

对我来说,这是你问题中真正有趣的部分。String被桥接到NSString,所以大多数NSString方法直接作用于String。你可以自由地使用它们,不需要思考。例如,这正如你所期望的那样:

// delete all spaces from Swift String stateName
stateName = stateName.stringByReplacingOccurrencesOfString(" ", withString:"")

But, as so often happens, "I got my mojo workin' but it just don't work on you." You just happened to pick one of the rare cases where a parallel identically named Swift method exists, and in a case like that, the Swift method overshadows the Objective-C method. Thus, when you say str.substringWithRange, Swift thinks you mean the Swift method rather than the NSString method — and then you are hosed, because the Swift method expects a Range<String.Index>, and you don't know how to make one of those.

最简单的办法就是阻止霉霉这样做,明确地说:

let x = (str as NSString).substringWithRange(NSMakeRange(0, 3))

注意,这里没有涉及到重大的额外工作。“转换”并不意味着“转换”;String实际上是一个NSString。我们只是告诉Swift为了这一行代码的目的如何看待这个变量。

整个事情中真正奇怪的部分是导致所有这些麻烦的Swift方法是没有记录的。我不知道它的定义是什么;它不在NSString头文件中也不在Swift头文件中。

一旦找到正确的语法,它比这里的任何答案都要简单得多。

我想把[和]

let myString = "[ABCDEFGHI]"
let startIndex = advance(myString.startIndex, 1) //advance as much as you like
let endIndex = advance(myString.endIndex, -1)
let range = startIndex..<endIndex
let myNewString = myString.substringWithRange( range )

结果是"ABCDEFGHI" startIndex和endIndex也可以用在

let mySubString = myString.substringFromIndex(startIndex)

等等!

PS:正如注释中所指出的,在xcode 7和iOS9附带的swift 2中有一些语法变化!

请看这一页

如何在Swift 2.0中获取子字符串的示例代码

(i)起始索引的子字符串

输入:-

var str = "Swift is very powerful language!"
print(str)

str = str.substringToIndex(str.startIndex.advancedBy(5))
print(str)

输出:

Swift is very powerful language!
Swift

(ii)特定索引的子字符串

输入:-

var str = "Swift is very powerful language!"
print(str)

str = str.substringFromIndex(str.startIndex.advancedBy(6)).substringToIndex(str.startIndex.advancedBy(2))
print(str)

输出:

Swift is very powerful language!
is

希望对你有所帮助!