C#刪除指定目錄下文件（保留指定幾天前的日志文件）

         /// <summary>
        /// 插入日志公用方法
        /// </summary>
        /// <param name="msg"></param>
        public static void insertLogs(string msg)
        {
            //日志輸出盤符物理路徑
            string pf = ConfigurationManager.AppSettings["PF"];
            //判斷文件路徑是否存在，不存在則創建，記錄日志
            DateTime dt = DateTime.Now;

            DeleteLogs(pf);

            string filetxt = pf + dt.ToString("yyyy-MM-dd") + ".log";
            if (!Directory.Exists(pf))//如果不存在就創建file文件夾　　             　　              
            {
                Directory.CreateDirectory(@"" + pf + "");//創建某盤下該文件夾    
            }
            
            StreamWriter fs = new StreamWriter(filetxt, true, System.Text.Encoding.UTF8);
            msg = msg + "\r\n";

            fs.Write(msg);
            fs.Flush();
            fs.Close();
        }



       //刪除指定日期文件，保留7天
        private static void DeleteLogs(string dir)
        {
            int days = 7;
            //日志保留時長 單位：天
            string logsDay = ConfigurationManager.AppSettings["logsDay"];
            if (!string.IsNullOrEmpty(logsDay))
            {
                days = int.Parse(logsDay);
            }

            try
            {
                if (!Directory.Exists(dir))
                {
                    return;
                }
                var now = DateTime.Now;
                foreach (var f in Directory.GetFileSystemEntries(dir).Where(f => File.Exists(f)))
                {
                    var t = File.GetCreationTime(f);
                    var elapsedTicks = now.Ticks - t.Ticks;
                    var elaspsedSpan = new TimeSpan(elapsedTicks);
                    if (elaspsedSpan.TotalDays > days)
                    {
                        File.Delete(f);
                    }
                }
            }
            catch (Exception ex)
            {

            }
        }