Swift 4中的String,substring,Range,NSRange

Question

我使用以下代码String从以下代码获取子字符串NSRange:

func substring(with nsrange: NSRange) -> String? {
    guard let range = Range.init(nsrange)
        else { return nil }
    let start = UTF16Index(range.lowerBound)
    let end = UTF16Index(range.upperBound)
    return String(utf16[start..<end])
}

(来自:https://mjtsai.com/blog/2016/12/19/nsregularexpression-and-swift/)

当我编译与斯威夫特4(9B4的Xcode),我获取该声明两条线以下的错误start和end:

'init' is unavailable
'init' was obsoleted in Swift 4.0

我很困惑,因为我没有使用init.

我怎样才能解决这个问题？

Answer 1

使用Range(_,in :)将NSRange转换为Swift 4中的Range.

extension String {
    func substring(with nsrange: NSRange) -> Substring? {
        guard let range = Range(nsrange, in: self) else { return nil }
        return self[range]
    }
}

Answer 2

使用Swift 4,我们可以通过这种方式获得子串.

1. 来自索引的子串

   let originStr = "Test"
   let offset = 1
   let str = String(originStr.suffix(from: String.Index.init(encodedOffset: offset)))
   

2. 索引的子字符串

   let originStr = "Test"
   let offset = 1
   String(self.prefix(index))