private void dgvMaterial_CellContentClick(object sender, DataGridViewCellEventArgs e)

        {

            for (int i = ; i < dgvMaterial.Rows.Count; i++)

            {

                DataGridViewCheckBoxCell ck = dgvMaterial.Rows[i].Cells[] as DataGridViewCheckBoxCell;

                if (i != e.RowIndex)

                {

                    ck.Value = false;

                }

                else

                {

                    ck.Value = true;

                }

            }

        }