combobox in datagridview

how to get selectedindex chaned event in datagridviewcombobox column in C#.net.

  private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
        {
            int rowIndex = dataGridView1.CurrentCell.RowIndex;
            uid = Convert.ToInt32(dataGridView1.Rows[rowIndex].Cells["UserID"].Value.ToString());
            if (dataGridView1.CurrentCell.ColumnIndex == 1 && e.Control is ComboBox)
            {
                ComboBox comboBox = e.Control as ComboBox;
                comboBox.SelectedIndexChanged += LastColumnComboSelectionChanged;
            }

        }
        private void LastColumnComboSelectionChanged(object sender, EventArgs e)
        {
            var currentcell = dataGridView1.CurrentCellAddress;
            var sendingCB = sender as DataGridViewComboBoxEditingControl;
            DataGridViewTextBoxCell cel = (DataGridViewTextBoxCell)dataGridView1.Rows[currentcell.Y].Cells[0];
            cel.Value = sendingCB.EditingControlFormattedValue.ToString();
          UpdateQuery up = new UpdateQuery();

         up.updateaccesspermission(uid,cel.Value.ToString());
        }

i uses the above code..it shows an error