public async Task <MylistItemsGetResult> GetLoginUserMylistItemsAsync(IMylist mylist, int page, int pageSize, MylistSortKey sortKey, MylistSortOrder sortOrder)
        {
            if (mylist.UserId != _niconicoSession.UserId)
            {
                throw new ArgumentException();
            }

            if (mylist.MylistId.IsWatchAfterMylist)
            {
                var mylistItemsRes = await _niconicoSession.ToolkitContext.Mylist.LoginUser.GetWatchAfterItemsAsync(page, pageSize, sortKey, sortOrder);

                var res   = mylistItemsRes.Data.Mylist;
                var items = res.Items;
                foreach (var item in items)
                {
                    _loginUserMylistItemIdRepository.AddItem(item.ItemId, mylist.MylistId, item.WatchId);
                }

                return(new MylistItemsGetResult()
                {
                    MylistId = mylist.MylistId,
                    IsSuccess = true,
                    Items = items,
                    NicoVideoItems = items.Select(MylistDataToNicoVideoData).ToArray(),
                    TotalCount = (int)mylistItemsRes.Data.Mylist.TotalCount,
                    HeadPosition = page * pageSize,
                });
            }
            else
            {
                var mylistItemsRes = await _niconicoSession.ToolkitContext.Mylist.LoginUser.GetMylistItemsAsync(mylist.PlaylistId.Id, (int)page, (int)pageSize, sortKey, sortOrder);

                var res   = mylistItemsRes.Data.Mylist;
                var items = res.Items;
                foreach (var item in items)
                {
                    _loginUserMylistItemIdRepository.AddItem(item.ItemId, mylist.MylistId, item.WatchId);
                }

                return(new MylistItemsGetResult()
                {
                    MylistId = mylist.MylistId,
                    IsSuccess = true,
                    Items = items,
                    NicoVideoItems = items.Select(MylistDataToNicoVideoData).ToArray(),
                    TotalCount = (int)mylistItemsRes.Data.Mylist.TotalItemCount,
                    HeadPosition = page * pageSize,
                });
            }
        }