objective c - Why would subclassing NSFormatter prevent me from editing NSTextField's input? -

i'm trying format 2 nstextfields smpte time codes, have format: hh:mm:ss:ff. however, when user switches smpte code drop-frame, delimiter between ss , ff needs switch ; (hh:mm:ss;ff). this, i've subclassed nsformatter, , have working except 1 stubborn problem.

the text field accepts input fine, if highlight-replace, backspace, delete, or insert new characters text field, nsbeep , can't switch focus away text field. can input new text if delete whole text field first, not if try edit existing input. here implemented methods/overrides:

- (nsstring*)stringforobjectvalue:(id)obj {     if ( ! [obj iskindofclass:[nsnumber class]])     {         return nil;     }      nsmutablestring *string = [nsmutablestring stringwithstring:@"00:00:00:00"];      int length = (int)[[obj stringvalue] length];     int insertlocation = 9;      if (length == 1)     {         [string replacecharactersinrange:nsmakerange(10, 1) withstring:[obj stringvalue]];     }     else     {         while (length > 1)         {             nsstring *temp = [[obj stringvalue] substringfromindex:length-2];             [string replacecharactersinrange:nsmakerange(insertlocation, 2) withstring:temp];              obj = [nsnumber numberwithint:[obj intvalue]/100];             length -= 2;             insertlocation -= 3;         }          if (length == 1)         {             [string replacecharactersinrange:nsmakerange(insertlocation+1, 1) withstring:[obj stringvalue]];         }     }      return string; }  - (bool)getobjectvalue:(out __autoreleasing id *)obj forstring:(nsstring *)string errordescription:(out nsstring *__autoreleasing *)error {     int valueresult;     nsscanner *scanner;     bool returnvalue = no;      scanner = [nsscanner scannerwithstring: string];     [scanner scanstring:@":" intostring:null];     [scanner scanstring:@";" intostring:null];      if ([scanner scanint:&valueresult] && ([scanner isatend])) {         returnvalue = yes;         if (obj)         {             *obj = [nsnumber numberwithint:valueresult];         }     }      return returnvalue; } 

at least @ point, don't need validate input during editing, when editing finished. tried implementing ispartialstringvalid , returning yes, didn't seem either. appreciated!

ok, solved doing more testing. appears though why failing because getobjectvalue receiving string delimiters in them , not correctly removing them. replaced method this:

- (bool)getobjectvalue:(out __autoreleasing id *)obj forstring:(nsstring *)string errordescription:(out nsstring *__autoreleasing *)error {     nsstring *newstring = [string stringbyreplacingoccurrencesofstring:@":" withstring:@""];      if (obj)     {         *obj = [nsnumber numberwithint:[newstring intvalue]];         return yes;     }      return no; } 

now works perfectly.