protected void grdCategories_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
    {
        grdCategories.SelectedIndex = e.NewSelectedIndex;
        bindGridViewCategories();
        bindGridViewProducts(Convert.ToInt32(grdCategories.SelectedDataKey["categoryid"].ToString()));
    }

protected void bindGridViewProducts(int categoryID)
    {
        string connectionString = ConfigurationManager.ConnectionStrings["SqlConnectionString"].ToString();
        SqlConnection sqlCon = new SqlConnection(connectionString);

        try
        {
            SqlCommand sqlCmd = new SqlCommand("select * from products where "mailto:categoryid=@categoryid">categoryid=@categoryid", sqlCon);
            sqlCmd.CommandType = CommandType.Text;
            sqlCmd.Parameters.Add("@categoryid", SqlDbType.Int).Value = categoryID;
            SqlDataAdapter sqlAdp = new SqlDataAdapter(sqlCmd);
            DataSet myDataSet = new DataSet();
            sqlAdp.Fill(myDataSet);

            // Delay the current Thread to display
            // the UpdateProgress status
            // Not required in real projects
            System.Threading.Thread.Sleep(4000);

            grdProducts.DataSource = myDataSet;
            grdProducts.DataBind();
        }
        catch (Exception ex)
        {
            lblErrorMsg.Text = ex.Message;
        }
    }