private string GetKey(string areaId, string type, string date, string appId, string privateKey)

        {

            var hmac = HMACSHA1.Create();

            var publicKey = GetPublicKey(areaId, type, date, appId);

            var data = System.Text.Encoding.UTF8.GetBytes(publicKey);

            //密钥

            var key = System.Text.Encoding.UTF8.GetBytes(privateKey);

            hmac.Key = key;

            //对数据进行签名

            var signedData = hmac.ComputeHash(data);

            return Convert.ToBase64String(signedData);

        }

        private string GetPublicKey(string areaId, string type, string date, string appId)

        {

            return string.Format("http://open.weather.com.cn/data/?areaid={0}&type={1}&date={2}&appid={3}", areaId, type, date, appId);

        }

        /// <summary>

        /// 获取请求URL

        /// </summary>

        /// <param name="areaId">地区ID，例：北京=101010100</param>

        /// <param name="type">预警:alarm 实况:observe 指数:index 常规预报(24小时):forecast1d</param>

        /// <param name="date">日期,年月日时分,例：201410091040</param>

        /// <param name="appId"></param>

        /// <param name="privateKey"></param>

        /// <returns></returns>

        public string GetUrl(string areaId, string type, string date, string appId, string privateKey)

        {

            string key = GetKey(areaId, type, date, appId, privateKey);

            return string.Format("http://open.weather.com.cn/data/?areaid={0}&type={1}&date={2}&appid={3}&key={4}",

              areaId, type, date, appId.Substring(, ), HttpUtility.UrlEncodeUnicode(key));

        }