WPF判断日期是工作日还是节假日

public string IsHoliday(string date)
        {
            string url = @"http://www.easybots.cn/api/holiday.php?d=";
            url = url + date;
            HttpWebRequest httpRequest = (HttpWebRequest)WebRequest.Create(url);
            httpRequest.Timeout = 2000;
            httpRequest.Method = "GET";
            HttpWebResponse httpResponse = (HttpWebResponse)httpRequest.GetResponse();
            StreamReader sr = new StreamReader(httpResponse.GetResponseStream(), System.Text.Encoding.GetEncoding("gb2312"));
            string result = sr.ReadToEnd();
            result = result.Replace("\r", "").Replace("\n", "").Replace("\t", "");
            int status = (int)httpResponse.StatusCode;
            sr.Close();
            return result;
        }

private void DP_MouseLeave(object sender, MouseEventArgs e)
        {
            string date = Convert.ToDateTime(DP.Text.ToString()).ToString("yyyyMMdd");
            string num = IsHoliday(date).Substring(IsHoliday(date).Length-2, 1);
            switch(num)
            {
                case "0":
                    TB.Text = "工作日";
                    break;
                default:
                    TB.Text = "节假日";
                    break;
            }
        }