C# 数组 之间转换

List<string> strLen = new List<string>();
            if (!string.IsNullOrEmpty(group_id))
            {
                using (ManagementSystemContext ef = new ManagementSystemContext())
                {
                    List<GroupMapUserMapRoler> list = ef.GroupMapUserMapRolers.Where(a => a.group_id == group_id).ToList();
                    list.ForEach(p =>
                    {
                        var mm = ef.tBaseRolerMapPowers.Where(a => a.roler_name.Equals(p.roler_name)).Select(a => a.power_name);
                        foreach (var item in mm)
                        {
                            strLen.Add(item.ToString());
                        }
                    });
                    if (strLen.Count > 0)
                        strLen.Distinct();
                }
            }
            return string.Join(",", strLen);