Question

A user selects a song in my mp3 player. He proceeds to rename a song (thus highlighting the “name” column of that given song).

Let’s say he pastes in “The\nGreat\nSong”. By default, if the string formatter doesn’t allow newlines (which is what I want), the app will produce a beep.

How can I process the string before it is pasted? This is what I want: If the string is less than 200 characters long, and if it contains newlines, replace the newlines with spaces before the string actually gets pasted. If it is longer than 200 characters, just do what it would do by default (because I don’t want the user accidentally pasting his PhD thesis in there).

How can one do something like that?

Answer 1

Turns out it was probably easiest to just edit my NSFormatter subclass itself. Here is my NSFormatter method, in case anyone is interested:

- (BOOL)isPartialStringValid:(NSString *)partial
            newEditingString:(NSString **)newString
            errorDescription:(NSString **)errorString
{
  *errorString = nil;
  *newString = nil;

  if ([partial containsIllegal])
  {
    NSBeep();
    return NO;
  }
  else if ([partial containsNewline])
  {
    if ([partial length] > 200)
    {
      NSBeep();
      return NO;
    }
    else
    {
      *newString = [partial stringByReplacingOccurrencesOfString:@"\n" withString:@" "];
      return NO;
    }
  }
  else
    return YES;
}

Those two NSString category methods there are simply as follows:

- (BOOL)containsIllegal
{
  for (int i=0; i<[self length]; i++)
  {
    unichar currentChar = [self characterAtIndex:i];

    BOOL charIsIllegal = [[NSCharacterSet illegalCharacterSet] characterIsMember:currentChar];

    if (charIsIllegal)
      return YES;
  }
  return NO;
}

- (BOOL)containsNewline
{
  for (int i=0; i<[self length]; i++)
  {
    unichar currentChar = [self characterAtIndex:i];

    BOOL charIsNewLine = [[NSCharacterSet newlineCharacterSet] characterIsMember:currentChar];

    if (charIsNewLine)
      return YES;
  }
  return NO;
}