叉叉，原来是自带的，

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

{

    if ([string isEqualToString:@""] && (range.length == 1 && range.location == 0)) {

        self.mArrowBtn.hidden = YES;

        self.nArrowBtn.hidden = YES;

        return YES;

    }

    TTLog(@"%@",textField.text);

    if (textField.text.length > 0 || string.length > 0) {

        if (textField.tag == 10) {

            self.mArrowBtn.hidden = NO;

        }else{

            self.nArrowBtn.hidden = NO;

        }

    }else{

        self.mArrowBtn.hidden = YES;

        self.nArrowBtn.hidden = YES;

    }

    return YES;

}