How to refresh an ASP.NET GridView automatically after update

Question

I need update the GridView after send email to list of users registered in the table userTable.

The GridView is populated from 25 users at a time.

I send the email to 25 first users, updated the field SendEmail for ID user and now I need update the GridView and show the next 25 users and so on.

I have tried this solution but after send email and update field SendEmail for ID user I see always first 25 users.

What am I missing?

What's wrong with this code?

Thank you in advance.

My code c# asp net:

protected void btnSend_Click(object sender, EventArgs e)
{
    try
    {
        SmtpClient smtpClient = new SmtpClient();
        System.Net.Mail.MailMessage mailMessage = new System.Net.Mail.MailMessage();

        lbltotalcount.Text = string.Empty;

        foreach (GridViewRow grow in grvCustomers.Rows)
        {
            try
            {
                ID = grow.Cells[0].Text.Trim();
                name = grow.Cells[1].Text.Trim();
                email = grow.Cells[2].Text.Trim();

                //Send email;

                using (OdbcConnection conn =
                                  new OdbcConnection(ConfigurationManager.ConnectionStrings["cs"].ConnectionString))
                {
                    sql1 = " UPDATE userTable SET `SendEmail` = 1 WHERE ID = ?; ";

                    using (OdbcCommand cmd = new OdbcCommand(sql1, conn))
                    {
                        try
                        {
                            conn.Open();
                            cmd.Parameters.AddWithValue("param1", ID.ToString());                                
                            cmd.ExecuteNonQuery();
                            Response.Write(sql1 + "<br /><br />");
                            btnBind.DataBind();
                        }
                        catch (Exception ex)
                        {
                            Response.Write("Send Email Failed." + ex.Message);
                        }
                        finally
                        {
                            conn.Close();
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }
        }
    }
    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }
}

protected void btnBind_Click(object sender, EventArgs e)
{
    sql = " SELECT * from userTable WHERE `SendEmail` = 0 LIMIT 25; ";

    using (OdbcConnection conn =
                      new OdbcConnection(ConfigurationManager.ConnectionStrings["cs"].ConnectionString))
    {
        conn.Open();
        using (OdbcCommand cmd = new OdbcCommand(sql, conn))
        {
            try
            {
                OdbcDataAdapter adp = new OdbcDataAdapter(cmd);
                DataSet ds = new DataSet();
                adp.Fill(ds);
                grvCustomers.DataSource = ds;
                grvCustomers.DataBind();
                lbltotalcount.Text = grvCustomers.Rows.Count.ToString();
            }
            catch (Exception ex)
            {
                Response.Write("Send Email Failed." + ex.Message);
            }
            finally
            {
                conn.Close();
            }

            btnBind.Visible = false;
        }
    }
}

edit #1

protected void btnBind_Click(object sender, EventArgs e)
{
    BindGrid();
}



protected void btnSend_Click(object sender, EventArgs e)
{
    try
    {
        SmtpClient smtpClient = new SmtpClient();
        System.Net.Mail.MailMessage mailMessage = new System.Net.Mail.MailMessage();

        lbltotalcount.Text = string.Empty;

        foreach (GridViewRow grow in grvCustomers.Rows)
        {
            try
            {
                ID = grow.Cells[0].Text.Trim();
                name = grow.Cells[1].Text.Trim();
                email = grow.Cells[2].Text.Trim();

                //Send email;

                using (OdbcConnection conn =
                                  new OdbcConnection(ConfigurationManager.ConnectionStrings["cs"].ConnectionString))
                {
                    sql1 = " UPDATE userTable SET `SendEmail` = 1 WHERE ID = ?; ";

                    using (OdbcCommand cmd = new OdbcCommand(sql1, conn))
                    {
                        try
                        {
                            conn.Open();
                            cmd.Parameters.AddWithValue("param1", ID.ToString());                                
                            cmd.ExecuteNonQuery();
                            Response.Write(sql1 + "<br /><br />");

                            BindGrid();

                        }
                        catch (Exception ex)
                        {
                            Response.Write("Send Email Failed." + ex.Message);
                        }
                        finally
                        {
                            conn.Close();
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Response.Write(ex.Message);
            }
        }
    }
    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }
}

protected void BindGrid();
{
    sql = " SELECT * from userTable WHERE `SendEmail` = 0 LIMIT 25; ";

    using (OdbcConnection conn =
                      new OdbcConnection(ConfigurationManager.ConnectionStrings["cs"].ConnectionString))
    {
        conn.Open();
        using (OdbcCommand cmd = new OdbcCommand(sql, conn))
        {
            try
            {
                OdbcDataAdapter adp = new OdbcDataAdapter(cmd);
                DataSet ds = new DataSet();
                adp.Fill(ds);
                grvCustomers.DataSource = ds;
                grvCustomers.DataBind();
                lbltotalcount.Text = grvCustomers.Rows.Count.ToString();
            }
            catch (Exception ex)
            {
                Response.Write("Send Email Failed." + ex.Message);
            }
            finally
            {
                conn.Close();
            }

            btnBind.Visible = false;
        }
    }
}

Answer 1

btnBind.DataBind();

This doesn't bind the grid, it binds the button. You need to re-bind the grid itself. First abstract that logic into its own method:

private void BindGrid()
{
    // basically all the code from btnBind_Click
}

Then call it from your handlers. For starters:

protected void btnBind_Click(object sender, EventArgs e)
{
    BindGrid();
}

Then also in your logic after sending the emails:

cmd.ExecuteNonQuery();
Response.Write(sql1 + "<br /><br />");
BindGrid();

Answer 2

protected void btnSend_Click(object sender, EventArgs e)
{
 after send mail and update table. then rebind data to gridview, 
 For example:
    try
    {
       //send email

    //it will bind next 25 records
    btnBind_Click(sender, e);
    }
 }