Повышение видимости символов по умолчанию из статической в ​​общую библиотеку

-(BOOL)isValidString:(NSString *)string{
    NSString *regex = @"[A-Z0-9a-z]*";
    NSPredicate *regTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regex];
    if ([regTest evaluateWithObject:string]) {
        return YES;
    }
    return NO;
}

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    if ([string length] == 0)
        return YES;
    if ([string length] > 0 && [string length] <=20) {
        NSString *newString = [textField text];
        newString = [newString stringByReplacingCharactersInRange:range withString:string];

        return [self isValidString:newString];
    } else {
        return NO;
    }
}