文件大小的单位转换方法

        /// <summary>
        /// 单位转换
        /// </summary>
        /// <param name="b">字节</param>
        /// <returns></returns>
        public string GetFileSize(double b)
        {
            var units = new[] {"", "K", "M", "G", "T" };
            var i = 0;
            while (b >= 1024&&i<4)
            {
                b /= 1024.0;
                i++;
            }
            return $"{b:0.00} {units[i]}B";
        }