distance(from:to :)’不可用:任何String视图索引转换都可能在Swift 4中失败;请打开可选索引

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我试图将我的应用程序迁移到 Swift 4,Xcode 9.我收到此错误.它来自第三方框架.

distance(from:to:)’ is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices

  1. func nsRange(from range: Range<String.Index>) -> NSRange {
  2. let utf16view = self.utf16
  3. let from = range.lowerBound.samePosition(in: utf16view)
  4. let to = range.upperBound.samePosition(in: utf16view)
  5. return NSMakeRange(utf16view.distance(from: utf16view.startIndex,to: from),// Error: distance(from:to:)' is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices
  6. utf16view.distance(from: from,to: to))// Error: distance(from:to:)' is unavailable: Any String view index conversion can fail in Swift 4; please unwrap the optional indices
  7. }
你可以简单地打开这样的可选索引:
  1. func nsRange(from range: Range<String.Index>) -> NSRange? {
  2. let utf16view = self.utf16
  3. if let from = range.lowerBound.samePosition(in: utf16view),let to = range.upperBound.samePosition(in: utf16view) {
  4. return NSMakeRange(utf16view.distance(from: utf16view.startIndex,utf16view.distance(from: from,to: to))
  5. }
  6. return nil
  7. }

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