获取目录下面最新修改的文件

 /// <summary>
        /// 获取日志目录下面最新的日志文件
        /// </summary>
        /// <returns></returns>
        public static string GetLatestLogFile()
        {
            string filepath = ConfigurationManager.AppSettings["IISlogDir"].ToString();
            if (!Directory.Exists(filepath))
            {
                LogHelper.WriteLog("error", "", "目录不存在");
            }
            else
            {
                var lastfilepath = (from f in Directory.GetFiles(filepath)
                                    let fi = new FileInfo(f)
                                    orderby fi.CreationTime descending
                                    select fi.FullName).FirstOrDefault();
                if (string.IsNullOrEmpty(lastfilepath))
                {
                    LogHelper.WriteLog("error", "", "日志文件夹下面没有日志文件");
                }
                filepath = lastfilepath;
            }
            return filepath;
        }