TextField empty and filter out 'return' key

gistfile1.m

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    
    NSString *filteredString = [string stringByReplacingOccurrencesOfString:@"\n" withString:@""];
    
    NSInteger textLength = [textField.text length] - range.length + [filteredString length];
    
    if (textLength > 0) {
        self.redeemButton.enabled = YES;
    }
    else {
        self.redeemButton.enabled = NO;
    }
    
    return YES;
}