C how to set two columns comboboxcolumn in DataGridView to bind a secondary linkage effect of cascading events

After changing the company , The options in the Department column have also changed .
This dataGridView Is bound. userBindingSource
The company column DataGridViewComboBoxColumn Is bound. CoBindingSource
Department column DataGridViewComboBoxColumn The binding is deptBindingSource
These are all used vs2005 The automatically generated code does .
And then to dataGridView Added a listener . An event is triggered when the value of a cell in the company column changes .
The event code is as follows ：

try
{
    
Point a = dataGridView1.CurrentCellAddress;
int values = (int)this.dataGridView1.Rows[a.X].Cells[1].Value;
this.deptTableAdapter.FillBy(this.dataSet.dept, values);
}
catch (Exception ex)
{
    
MessageBox.Show(ex.Message);
}

For the company ComboBox Add event

dataGridView.EditingControlShowing += new DataGridViewEditingControlShowingEventHandler(dataGridView_EditingControlShowing);
private void dataGridView_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    
    if (dataGridView.CurrentCell.OwningColumn.Name.Equals(" company ") && e.Control is ComboBox)
    {
    
        (e.Control as ComboBox).SelectedValueChanged -= new EventHandler(ComboBox_SelectedValueChanged);
        (e.Control as ComboBox).SelectedValueChanged += new EventHandler(ComboBox_SelectedValueChanged);
    }
}

void ComboBox_SelectedValueChanged(object sender, EventArgs e)
{
    
   if ((sender as ComboBox).SelectedItem != null)
   {
    
        dataGridView.CurrentRow.Cells[" department "].Value = ((sender as ComboBox).SelectedItem as DataRowView)[" department "];
   }
}

  //  Build the actual data source of the table 

  DataTable dt = new DataTable();
  dt.Columns.Add("c_ID");
  dt.Columns.Add("d_ID");

  for (int i = 0; i < 10; i += 2)
      dt.Rows.Add(new object[] {
     i, i % 4 });

  dataGridView1.DataSource = dt;
  // First, build the first linkage data column 
  DataTable dt1 = new DataTable();
  dt1.Columns.Add("c_ID");
  dt1.Columns.Add("c_name");

 for (int i = 0; i < 10; i++)
      dt1.Rows.Add(new object[] {
     i, " company " + i.ToString() });
  // Create a drop-down column 
 DataGridViewComboBoxColumn cc = new DataGridViewComboBoxColumn();
 cc.DataSource = dt1;
 cc.HeaderText = " Corporate name ";
 cc.DisplayMember = "c_name";
 cc.ValueMember = "c_ID";
 cc.DataPropertyName = "c_ID";
 dataGridView1.Columns.Add ( cc);


 // Build the second level linkage data column 
 DataTable dt2 = new DataTable();
 dt2.Columns.Add("d_ID");
 dt2.Columns.Add("d_name");

 for (int i = 0; i < 4; i++)
     dt2.Rows.Add(new object[] {
     i, " department " + i.ToString() });
 // Create a drop-down column 
 DataGridViewComboBoxColumn c2 = new DataGridViewComboBoxColumn();
 c2.DataSource = dt2;
 c2.HeaderText = " department ";
 c2.DisplayMember = "d_name";
 c2.ValueMember = "d_ID";
 c2.DataPropertyName = "d_ID";
 dataGridView1.Columns.Add( c2);

  // Last hidden ID Column 
 dataGridView1.Columns[0].Visible = false;
 dataGridView1.Columns[1].Visible = false;