Displaying sum the values of the datagridview cell columns in datagridview cell row footer..

Question

This is the Code:

Form1.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.OleDb;
namespace Sum_datagridview_cell_row_footer
{
    public partial class Form1 : Form
    {
        string ConnectionString = System.Configuration.ConfigurationSettings.AppSettings["dsn"];
        OleDbCommand com;
        OleDbDataAdapter oledbda;
        DataSet ds;
        string str;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            bindgrid();
        }
        private void bindgrid()
        {
            OleDbConnection con = new OleDbConnection(ConnectionString);
            con.Open();
            str = "select * from product";
            com = new OleDbCommand(str, con);
            oledbda = new OleDbDataAdapter(com);
            ds = new DataSet();
            oledbda.Fill(ds, "product");
            dataGridView1.DataMember = "product";
            dataGridView1.DataSource = ds;
            con.Close();
            dataGridView1[0, dataGridView1.Rows.Count - 1].Value = "Total Sum";
            dataGridView1.Rows[dataGridView1.Rows.Count - 1].Cells[0].Style.BackColor = Color.Yellow;
            dataGridView1.Rows[dataGridView1.Rows.Count - 1].Cells[1].Style.ForeColor = Color.Red;
        }

        private void dataGridView1_DataSourceChanged(object sender, EventArgs e)
        {
            int sum = 0;

            for (int i = 0; i < dataGridView1.Rows.Count - 1; i++)
            {

                if (dataGridView1[1, i].Value != DBNull.Value)
                    sum += (int)dataGridView1[1, i].Value;
            }
            dataGridView1[1, dataGridView1.Rows.Count - 1].Value = sum;
        }

    }
}





It is displaying the sum. But when i click on that sum value complete row gets blank and after that in dosen't show any sum. So can you please help me.

Thanks in advance.