protected override void OnStart(string[] args)
        {
            StartLoad();
        }

        protected override void OnStop()
        {
            _Timer.Stop();
        }

CreateFilePath();//判断文件夹是否存在，不存在则创建
            //获取前一天日期
            string lastYear = DateTime.Now.AddDays(-1).Year.ToString();
            string lastMonth = DateTime.Now.AddDays(-1).Month.ToString();
            if (lastMonth.Length < 2) lastMonth = "0" + lastMonth;
            string lastDay = DateTime.Now.AddDays(-1).Day.ToString();
            if (lastDay.Length < 2) lastDay = "0" + lastDay;
            //获取当天日期
            string year = DateTime.Now.Year.ToString();
            string month = DateTime.Now.Month.ToString();
            if (month.Length < 2) month = "0" + month;
            string day = DateTime.Now.Day.ToString();
            if (day.Length < 2) day = "0" + day;
            //设置所有文件名
            string[] dates0 = { lastYear + "/" + lastMonth + "/" + lastDay, year + "/" + month + "/" + day };
            string[] dates = { lastYear + lastMonth + lastDay, year + month + day };
            string[] hours = { "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20", "21", "22", "23" };
            string[] minutes = { "15", "45" };
            int hLength = hours.Count();
            //遍历下载当天所有在线云图
            for (int i = 0; i < 2; i++)
            {
                string date = dates[i];
                string date0 = dates0[i];
                for (int j = 0; j < hLength; j++)
                {
                    string hour = hours[j];
                    for (int k = 0; k < 2; k++)
                    {
                        string minute = minutes[k];
                        string imageUrl = @"http://image.nmc.cn/product/" + date0 + @"/WXCL/SEVP_NSMC_WXCL_ASC_E99_ACHN_LNO_PY_" + date + hour + minute + "00000.JPG";
                        string[] s = imageUrl.Split('/');
                        string imageName = s[s.Count() - 1];

                        HttpWebRequest request = HttpWebRequest.Create(imageUrl) as HttpWebRequest;
                        HttpWebResponse response = null;
                        try
                        {
                            response = request.GetResponse() as HttpWebResponse;
                        }
                        catch (Exception)
                        {
                            continue;
                        }

                        if (response.StatusCode != HttpStatusCode.OK) continue;
                        Stream reader = response.GetResponseStream();
                        FileStream writer = new FileStream(_ImagePath + imageName, FileMode.OpenOrCreate, FileAccess.Write);
                        byte[] buff = new byte[512];
                        int c = 0; //实际读取的字节数
                        while ((c = reader.Read(buff, 0, buff.Length)) > 0)
                        {
                            writer.Write(buff, 0, c);
                        }
                        writer.Close();
                        writer.Dispose();
                        reader.Close();
                        reader.Dispose();
                        response.Close();
                    }
                }
            }