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

Question

Need to have an NSTextField with a text limit of 4 characters maximum and show always in upper case but can't figure out a good way of achieving that. I've tried to do it through a binding with a validation method but the validation only gets called when the control loses first responder and that's no good.

Temporarly I made it work by observing the notification NSControlTextDidChangeNotification on the text field and having it call the method:

- (void)textDidChange:(NSNotification*)notification {   NSTextField* textField = [notification object];   NSString* value = [textField stringValue];   if ([value length] > 4) {     [textField setStringValue:[[value uppercaseString] substringWithRange:NSMakeRange(0, 4)]];   } else {     [textField setStringValue:[value uppercaseString]];   } } 

But this surely isn't the best way of doing it. Any better suggestion?

Answer 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