Edit Data ใน DataGridView แล้วบันทึกลงฐานข้อมูลไม่ได้

private void Show_Data(string _txtIdDurRecei)
        {

            try
            {
                string connectionString = dc.Getdb.ToString();  //เรียกใช้ dbconnec
                conn = new MySqlConnection(connectionString);
                conn.Open();
                string sql = "SELECT dur_id, dur_name, durGroup_name, durtype_name, dur_detail, dur_amount, a.dur_price, unit_name, dur_date FROM tbl_durables";
                dt = new DataTable();
                da = new MySqlDataAdapter(sql, conn);
                da.Fill(dt);
                conn.Close();
                dgDisplay.DataSource = dt;
                dgDisplay.Columns.Clear();

                DataGridViewTextBoxColumn column;
                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "dur_id";
                column.HeaderText = "รหัสครุภัณฑ์";
                column.Width = 90;
                column.ReadOnly = true; 
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "dur_name";
                column.HeaderText = "ชื่อครุภัณฑ์";
                column.Width = 160;
                column.ReadOnly = false;
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "durGroup_name";
                column.HeaderText = "กลุ่มครุภัณฑ์";
                column.Width = 200;
                column.ReadOnly = true; 
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "durtype_name";
                column.HeaderText = "ประเภทครุภัณฑ์";
                column.Width = 130;
                column.ReadOnly = true; 
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "dur_detail";
                column.HeaderText = "รายละเอียด";
                column.Width = 155;
                column.ReadOnly = false; 
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "dur_amount";
                column.HeaderText = "จำนวน";
                column.Width = 50;
                column.ReadOnly = true; 
                column.DefaultCellStyle.Alignment = DataGridViewContentAlignment.BottomRight;
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "dur_price";
                column.HeaderText = "ราคา";
                column.Width = 80;
                column.ReadOnly = false; 
                column.DefaultCellStyle.Format = "#,##0.0";
                column.DefaultCellStyle.Alignment = DataGridViewContentAlignment.BottomRight;
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "unit_name";
                column.HeaderText = "หน่วย";
                column.Width = 70;
                column.ReadOnly = false; 
                this.dgDisplay.Columns.Add(column);

                column = new DataGridViewTextBoxColumn();
                column.DataPropertyName = "dur_date";
                column.HeaderText = "วันที่";
                column.Width = 85;
                column.ReadOnly = true; 
                this.dgDisplay.Columns.Add(column);

                DataGridViewCheckBoxColumn ColumnCheckBox = new DataGridViewCheckBoxColumn();
                ColumnCheckBox.Width = 45;
                ColumnCheckBox.DataPropertyName = "Select";
                ColumnCheckBox.HeaderText = "เลือก";
                this.dgDisplay.Columns.Add(ColumnCheckBox);

                dt = null;
            }
            catch (Exception ex) { MessageBox.Show(ex.Message); }

        }

try
            {
                da = new MySqlDataAdapter();
                dt = new DataTable();
                da.Update(dt);
                MessageBox.Show("Changes Done");
            }

            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }