static void GetFiles(List<string> arr, string dir)
        {

            arr.AddRange(Directory.GetFiles(dir));
            var subDir = Directory.GetDirectories(dir).ToList();
            if (subDir != null && subDir.Count > 0)
                subDir.ForEach(j =>
                {
                    GetFiles(arr, j);
                });

        }

  List<string> path = new List<string>();
            GetFiles(path, @"C:\Users\Administrator\Desktop\新建文件夹");