CapDemo.GetQuestion.cmb_Catalogue_SelectedIndexChanged C# (CSharp) Метод

        private void cmb_Catalogue_SelectedIndexChanged(object sender, EventArgs e)
        {
            dgv_Question.Columns.Clear();
            Catalogue catalogue = new Catalogue();
            CatalogueBL CatBL = new CatalogueBL();

            List<DO.Catalogue> CatList;
            CatList = CatBL.GetCatalogue();
            if (CatList != null)
                for (int i = 0; i < CatList.Count; i++)
                {
                    if (cmb_Catalogue.SelectedItem.ToString() == CatList.ElementAt(i).NameCatalogue)
                    {
                        catalogue.IDCatalogue = CatList.ElementAt(i).IDCatalogue;
                    }
                }

            QuestionBL QuestionBL = new QuestionBL();
            List<DO.Question> QuestionList;
            QuestionList = QuestionBL.GetQuestionByCatalogue(catalogue);
            if (QuestionList != null)
            {
                dgv_Question.DataSource = QuestionList;
            }

            dgv_Question.Columns["IDCatalogue"].Visible = false;
            dgv_Question.Columns["IDQuestion"].Visible = false;
            dgv_Question.Columns["AnswerContent"].Visible = false;
            dgv_Question.Columns["Date"].Visible = false;
            dgv_Question.Columns["NameCatalogue"].Visible = false;
            dgv_Question.Columns["Catalogue"].Visible = false;

            dgv_Question.Columns["Sequence"].AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;
            dgv_Question.Columns["TypeQuestion"].AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;
            dgv_Question.Columns["NameCatalogue"].AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;
            dgv_Question.Columns["QuestionTitle"].AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;

            dgv_Question.Columns["Sequence"].HeaderText = "STT";
            dgv_Question.Columns["TypeQuestion"].HeaderText = "Loại Câu Hỏi";
            dgv_Question.Columns["NameQuestion"].HeaderText = "Nội Dung Câu Hỏi";
            dgv_Question.Columns["QuestionTitle"].HeaderText = "Tên Câu Hỏi";

            dgv_Question.Columns["Sequence"].ReadOnly = true;
            dgv_Question.Columns["TypeQuestion"].ReadOnly = true;
            dgv_Question.Columns["NameQuestion"].ReadOnly = true;
            dgv_Question.Columns["QuestionTitle"].ReadOnly = true;

            DataGridViewCheckBoxColumn CheckColumn = new DataGridViewCheckBoxColumn();
            CheckColumn.Name = "Check";
            dgv_Question.Columns.Add(CheckColumn);
            dgv_Question.Columns["Check"].HeaderText = "Chọn";
            dgv_Question.Columns["Check"].AutoSizeMode = DataGridViewAutoSizeColumnMode.DisplayedCells;

            chk_CheckAll.Checked = false;
        }