How to perform selectedIndexChanged event of dataGridViewcomboBoxColumn in WinForm

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C#2.0

C#

In my WinForm Application, I used a dataGridView1 control. In this dataGridView1 I added three dataGridViewcomboBoxColumn namely: ProductCode, SelectCategory and SelectCategory. Whenever the user will select category from ProductCode dataGridViewcomboBoxColumn, data should be automatically retrieved from SQL Server 2005 database in SelectCategory and ProductName dataGridViewcomboBoxColumn. I am very new in this field.Please help me.
I wrote some code for it: but it not working

private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
       {
           if (dataGridView1.CurrentCell.ColumnIndex == 2)
           {
               ComboBox comboBox = e.Control as ComboBox;
               if (comboBox != null)
               {
                   comboBox.SelectedIndexChanged += new EventHandler(comboBox_SelecteIndexChanged);
               }

           }
       }
       void comboBox_SelecteIndexChanged(object sender, EventArgs e)
       {
           try
           {
               DataSet ds = new DataSet();
               string str = "select ProductCategory,ProductName from Product_Details where ProductID='" + dataGridView1.Rows[intRownum].Cells[2].Value + "'";
               SqlConnection con = new SqlConnection(Class1.cs);
               con.Open();
               SqlCommand cmd = new SqlCommand(str, con);
               SqlDataAdapter da = new SqlDataAdapter(cmd);
               da.Fill(ds, "Product_Details");
               if (ds.Tables["Product_Details"].Rows.Count > 0)
               {
                   dataGridView1.Rows[intRownum].Cells[3].Value = ds.Tables["Product_Details"].Rows[intRownum][0].ToString();
                   dataGridView1.Rows[intRownum].Cells[4].Value = ds.Tables["Product_Details"].Rows[intRownum][1].ToString();
                   dataGridView1.Update();
               }
           }
           catch (Exception ex)
           {
               MessageBox.Show(ex.Message.ToString());
           }

       }