How to limit NSTextField text length and keep it always upper case?

Solution 1:

I did as Graham Lee suggested and it works fine, here's the custom formatter code:

UPDATED: Added fix reported by Dave Gallagher. Thanks!

@interface CustomTextFieldFormatter : NSFormatter {
  int maxLength;
}
- (void)setMaximumLength:(int)len;
- (int)maximumLength;

@end

@implementation CustomTextFieldFormatter

- (id)init {

   if(self = [super init]){

      maxLength = INT_MAX;
   }

  return self;
}

- (void)setMaximumLength:(int)len {
  maxLength = len;
}

- (int)maximumLength {
  return maxLength;
}

- (NSString *)stringForObjectValue:(id)object {
  return (NSString *)object;
}

- (BOOL)getObjectValue:(id *)object forString:(NSString *)string errorDescription:(NSString **)error {
  *object = string;
  return YES;
}

- (BOOL)isPartialStringValid:(NSString **)partialStringPtr
   proposedSelectedRange:(NSRangePointer)proposedSelRangePtr
          originalString:(NSString *)origString
   originalSelectedRange:(NSRange)origSelRange
        errorDescription:(NSString **)error {
    if ([*partialStringPtr length] > maxLength) {
        return NO;
    }

    if (![*partialStringPtr isEqual:[*partialStringPtr uppercaseString]]) {
      *partialStringPtr = [*partialStringPtr uppercaseString];
      return NO;
    }

    return YES;
}

- (NSAttributedString *)attributedStringForObjectValue:(id)anObject withDefaultAttributes:(NSDictionary *)attributes {
  return nil;
}

@end

Solution 2:

Have you tried attaching a custom NSFormatter subclass?

Solution 3:

In the above example where I commented, this is bad:

// Don't use:
- (BOOL)isPartialStringValid:(NSString *)partialString
            newEditingString:(NSString **)newString
            errorDescription:(NSString **)error
{
    if ((int)[partialString length] > maxLength)
    {
        *newString = nil;
        return NO;
    }
}

Use this (or something like it) instead:

// Good to use:
- (BOOL)isPartialStringValid:(NSString **)partialStringPtr
       proposedSelectedRange:(NSRangePointer)proposedSelRangePtr
              originalString:(NSString *)origString
       originalSelectedRange:(NSRange)origSelRange
            errorDescription:(NSString **)error
{
    int size = [*partialStringPtr length];
    if ( size > maxLength )
    {
        return NO;
    }
    return YES;
}

Both are NSFormatter methods. The first one has an issue. Say you limit text-entry to 10 characters. If you type characters in one-by-one into an NSTextField, it'll work fine and prevent users from going beyond 10 characters.

However, if a user was to paste a string of, say, 25 characters into the Text Field, what'll happen is something like this:

1) User will paste into TextField

2) TextField will accept the string of characters

3) TextField will apply the formatter to the "last" character in the 25-length string

4) Formatter does stuff to the "last" character in the 25-length string, ignoring the rest

5) TextField will end up with 25 characters in it, even though it's limited to 10.

This is because, I believe, the first method only applies to the "very last character" typed into an NSTextField. The second method shown above applies to "all characters" typed into the NSTextField. So it's immune to the "paste" exploit.

I discovered this just now trying to break my application, and am not an expert on NSFormatter, so please correct me if I'm wrong. And very much thanks to you carlosb for posting that example. It helped a LOT! :)