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

Answer 1

The custom NSFormatter that Graham Lee suggested is the best approach.

A simple kludge would be to set your view controller as the text field's delegate then just block any edit that involves non-uppercase or makes the length longer than 4:

- (BOOL)textField:(UITextField *)textField
    shouldChangeCharactersInRange:(NSRange)range
    replacementString:(NSString *)string
{
    NSMutableString *newValue = [[textField.text mutableCopy] autorelease];
    [newValue replaceCharactersInRange:range withString:string];

    NSCharacterSet *nonUppercase =
        [[NSCharacterSet uppercaseLetterCharacterSet] invertedSet];
    if ([newValue length] > 4 ||
        [newValue rangeOfCharacterFromSet:nonUppercase].location !=
            NSNotFound)
    {
       return NO;
    }

    return YES;
}