NSRange to Range String Index

Question

How can I convert NSRange to Range lt String Index gt  in Swift    I want to use the following UITextFieldDelegate method       func textField textField  UITextField           shouldChangeCharactersInRange range  NSRange          replacementString string  String   - gt  Bool    textField text stringByReplacingCharactersInRange      withString  string

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In Swift 2 0 assuming func textField textField  UITextField  shouldChangeCharactersInRange range  NSRange  replacementString string  String  - gt  Bool     var oldString   textfield text  let newRange   oldString startIndex advancedBy range location    lt oldString startIndex advancedBy range location   range length  let newString   oldString stringByReplacingCharactersInRange newRange  withString  string

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Here s my best effort  But this cannot check or detect wrong input argument   extension String            r  Must correctly select proper UTF-16 code-unit range  Wrong range will produce wrong result      public func convertRangeFromNSRange r NSRange  - gt  Range lt String Index gt            let a        self as NSString  substringToIndex r location          let b        self as NSString  substringWithRange r           let n1      distance a startIndex  a endIndex          let n2      distance b startIndex  b endIndex           let i1      advance startIndex  n1          let i2      advance i1  n2           return  Range lt String Index gt  start  i1  end  i2           let s          println s s convertRangeFromNSRange NSRange location  4  length  2              Proper range  Produces correct result  println s s convertRangeFromNSRange NSRange location  0  length  4              Proper range  Produces correct result  println s s convertRangeFromNSRange NSRange location  0  length  2              Improper range  Produces wrong result  println s s convertRangeFromNSRange NSRange location  0  length  1              Improper range  Produces wrong result    Result         Details  NSRange from NSString counts UTF-16 code-units  And Range lt String Index gt  from Swift String is an opaque relative type which provides only equality and navigation operations  This is intentionally hidden design   Though the Range lt String Index gt  seem to be mapped to UTF-16 code-unit offset  that is just an implementation detail  and I couldn t find any mention about any guarantee  That means the implementation details can be changed at any time  Internal representation of Swift String is not pretty defined  and I cannot rely on it   NSRange values can be directly mapped to String UTF16View indexes  But there s no method to convert it into String Index   Swift String Index is index to iterate Swift Character which is an Unicode grapheme cluster  Then  you must provide proper NSRange which selects correct grapheme clusters  If you provide wrong range like the above example  it will produce wrong result because proper grapheme cluster range couldn t be figured out    If there s a guarantee that the String Index is UTF-16 code-unit offset  then problem becomes simple  But it is unlikely to happen   Inverse conversion  Anyway the inverse conversion can be done precisely   extension String           O 1  if  self  is optimised to use UTF-16          O n  otherwise      public func convertRangeToNSRange r Range lt String Index gt   - gt  NSRange           let a       substringToIndex r startIndex          let b       substringWithRange r           return  NSRange location  a utf16Count  length  b utf16Count          println convertRangeToNSRange s startIndex   lt s endIndex   println convertRangeToNSRange s startIndex successor     lt s endIndex     Result    0 6   4 2

User · Answer

A riff on the great answer by  Emilie  not a replacement competing answer   Xcode6-Beta5   var original       This is a test  var replacement        var startIndex   advance original startIndex  1     Start at the second character var endIndex     advance startIndex  2     point ahead two characters var range        Range start startIndex  end endIndex  var final   original stringByReplacingCharactersInRange range  withString replacement   println  start index    startIndex    println  end index      endIndex    println  range          range    println  original       original    println  final          final      Output     start index  4 end index    7 range        4   lt 7 original     This is a test final         his is a test   Notice the indexes account for multiple code units  The flag  REGIONAL INDICATOR SYMBOL LETTERS ES  is 8 bytes and the  FACE WITH TEARS OF JOY  is 4 bytes   In this particular case it turns out that the number of bytes is the same for UTF-8  UTF-16 and UTF-32 representations    Wrapping it in a func   func replaceString  string String   with String   start Int   length Int  - gt String       var startIndex   advance original startIndex  start     Start at the second character     var endIndex     advance startIndex  length     point ahead two characters     var range        Range start startIndex  end endIndex      var final   original stringByReplacingCharactersInRange range  withString  replacement      return final    var newString   replaceString string original  with replacement  start 1  length 2  println  newString   newString      Output     newString   his is a test

User · Answer

The NSString version  as opposed to Swift String  of replacingCharacters in  NSRange  with  NSString  accepts an NSRange  so one simple solution is to convert String to NSString first  The delegate and replacement method names are slightly different in Swift 3 and 2  so depending on which Swift you re using   Swift 3 0  func textField   textField  UITextField                 shouldChangeCharactersIn range  NSRange                 replacementString string  String  - gt  Bool      let nsString   textField text as NSString    let newString   nsString  replacingCharacters in  range  with  string      Swift 2 x  func textField textField  UITextField                 shouldChangeCharactersInRange range  NSRange                 replacementString string  String  - gt  Bool        let nsString   textField text as NSString      let newString   nsString  stringByReplacingCharactersInRange range  withString  string

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I ve found the cleanest swift2 only solution is to create a category on NSRange   extension NSRange       func stringRangeForText string  String  - gt  Range lt String Index gt            let start   string startIndex advancedBy self location          let end   start advancedBy self length          return Range lt String Index gt  start  start  end  end            And then call it from for text field delegate function   func textField textField  UITextField  shouldChangeCharactersInRange range  NSRange  replacementString string  String  - gt  Bool       let range   range stringRangeForText textField text      let output   textField text stringByReplacingCharactersInRange range  withString  string          your code goes here          return true

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As of Swift 4  Xcode 9   the Swift standard library provides methods to convert between Swift string ranges  Range lt String Index gt    and NSString ranges  NSRange   Example   let str    abc  let r1   str range of           String range to NSRange  let n1   NSRange r1  in  str  print  str as NSString  substring with  n1           NSRange back to String range  let r2   Range n1  in  str   print str r2         Therefore the text replacement in the text field delegate method can now be done as  func textField   textField  UITextField                 shouldChangeCharactersIn range  NSRange                 replacementString string  String  - gt  Bool        if let oldString   textField text           let newString   oldString replacingCharacters in  Range range  in  oldString                                                          with  string                                         Older answers for Swift 3 and earlier    As of Swift 1 2  String Index has an initializer  init    utf16Index  UTF16Index  within characters  String    which can be used to convert NSRange to Range lt String Index gt  correctly  including all cases of Emojis  Regional Indicators or other extended grapheme clusters  without intermediate conversion to an NSString   extension String       func rangeFromNSRange nsRange   NSRange  - gt  Range lt String Index gt             let from16   advance utf16 startIndex  nsRange location  utf16 endIndex          let to16   advance from16  nsRange length  utf16 endIndex          if let from   String Index from16  within  self               let to   String Index to16  within  self                    return from    lt  to                   return nil           This method returns an optional string range because not all NSRanges are valid for a given Swift string   The UITextFieldDelegate delegate method can then be written as  func textField textField  UITextField  shouldChangeCharactersInRange range  NSRange  replacementString string  String  - gt  Bool        if let swRange   textField text rangeFromNSRange range            let newString   textField text stringByReplacingCharactersInRange swRange  withString  string                           return true     The inverse conversion is  extension String       func NSRangeFromRange range   Range lt String Index gt   - gt  NSRange           let utf16view   self utf16         let from   String UTF16View Index range startIndex  within  utf16view           let to   String UTF16View Index range endIndex  within  utf16view          return NSMakeRange from - utf16view startIndex  to - from            A simple test   let str    abc  let r1   str rangeOfString          String range to NSRange  let n1   str NSRangeFromRange r1  println  str as NSString  substringWithRange n1           NSRange back to String range  let r2   str rangeFromNSRange n1   println str substringWithRange r2         Update for Swift 2   The Swift 2 version of rangeFromNSRange   was already given  by Serhii Yakovenko in this answer  I am including it here for completeness   extension String       func rangeFromNSRange nsRange   NSRange  - gt  Range lt String Index gt             let from16   utf16 startIndex advancedBy nsRange location  limit  utf16 endIndex          let to16   from16 advancedBy nsRange length  limit  utf16 endIndex          if let from   String Index from16  within  self               let to   String Index to16  within  self                    return from    lt  to                   return nil           The Swift 2 version of NSRangeFromRange   is  extension String       func NSRangeFromRange range   Range lt String Index gt   - gt  NSRange           let utf16view   self utf16         let from   String UTF16View Index range startIndex  within  utf16view          let to   String UTF16View Index range endIndex  within  utf16view          return NSMakeRange utf16view startIndex distanceTo from   from distanceTo to             Update for Swift 3  Xcode 8    extension String       func nsRange from range  Range lt String Index gt   - gt  NSRange           let from   range lowerBound samePosition in  utf16          let to   range upperBound samePosition in  utf16          return NSRange location  utf16 distance from  utf16 startIndex  to  from                          length  utf16 distance from  from  to  to            extension String       func range from nsRange  NSRange  - gt  Range lt String Index gt             guard             let from16   utf16 index utf16 startIndex  offsetBy  nsRange location  limitedBy  utf16 endIndex               let to16   utf16 index utf16 startIndex  offsetBy  nsRange location   nsRange length  limitedBy  utf16 endIndex               let from   from16 samePosition in  self               let to   to16 samePosition in  self              else   return nil           return from    lt  to           Example   let str    abc  let r1   str range of           String range to NSRange  let n1   str nsRange from  r1  print  str as NSString  substring with  n1           NSRange back to String range  let r2   str range from  n1   print str substring with  r2

User · Answer

You need to use Range lt String Index gt  instead of the classic NSRange  The way I do it  maybe there is a better way  is by taking the string s String Index a moving it with advance   I don t know what range you are trying to replace  but let s pretend you want to replace the first 2 characters   var start   textField text startIndex    Start at the string s start index var end   advance textField text startIndex  2     Take start index and advance 2 characters forward var range  Range lt String Index gt    Range lt String Index gt  start  start end  end   textField text stringByReplacingCharactersInRange range  withString  string

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This answer by Martin R seems to be correct because it accounts for Unicode   However at the time of the post  Swift 1  his code doesn t compile in Swift 2 0  Xcode 7   because they removed advance   function  Updated version is below   Swift 2  extension String       func rangeFromNSRange nsRange   NSRange  - gt  Range lt String Index gt             let from16   utf16 startIndex advancedBy nsRange location  limit  utf16 endIndex          let to16   from16 advancedBy nsRange length  limit  utf16 endIndex          if let from   String Index from16  within  self               let to   String Index to16  within  self                    return from    lt  to                   return nil           Swift 3  extension String       func rangeFromNSRange nsRange   NSRange  - gt  Range lt String Index gt             if let from16   utf16 index utf16 startIndex  offsetBy  nsRange location  limitedBy  utf16 endIndex               let to16   utf16 index from16  offsetBy  nsRange length  limitedBy  utf16 endIndex               let from   String Index from16  within  self               let to   String Index to16  within  self                    return from    lt  to                   return nil           Swift 4  extension String       func rangeFromNSRange nsRange   NSRange  - gt  Range lt String Index gt             return Range nsRange  in  self

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In the accepted answer I find the optionals cumbersome  This works with Swift 3 and seems to have no problem with emojis    func textField   textField  UITextField         shouldChangeCharactersIn range  NSRange         replacementString string  String  - gt  Bool      guard let value   textField text else  return false     there may be a reason for returning true in this case but I can t think of it      now value is a String  not an optional String    let valueAfterChange    value as NSString  replacingCharacters in  range  with  string       valueAfterChange is a String  not an optional String       now do whatever processing is required    return true     or false  as required

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The Swift 3 0 beta official documentation has provided its standard solution for this situation under the title String UTF16View in section UTF16View Elements Match NSString Characters title

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func textField textField  UITextField  shouldChangeCharactersInRange range  NSRange  replacementString string  String  - gt  Bool           let strString     textField text   as NSString  stringByReplacingCharactersInRange range  withString  string

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This is similar to Emilie s answer however since you asked specifically how to convert the NSRange to Range lt String Index gt  you would do something like this   func textField textField  UITextField  shouldChangeCharactersInRange range  NSRange  replacementString string  String  - gt  Bool         let start   advance textField text startIndex  range location        let end   advance start  range length        let swiftRange   Range lt String Index gt  start  start  end  end

User · Answer

extension StringProtocol where Index    String Index        func nsRange of string  String  - gt  NSRange            guard let range   self range of  string  else    return nil           return NSRange range  in  self

[nsstring] NSRange to Range<String.Index>

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