Cannot update selected lines from data in gridview - asp.net

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Web.Services.Description;
namespace Lab06
{
public partial class AssignmentAttendance : System.Web.UI.Page
{
Student sStudent = new Student();
Attendance aAttendance = new Attendance();
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
bind();
}
}
protected void bind()
{
List<Student> acclist = new List<Student>();
acclist = sStudent.getAccountAll();
GridView1.DataSource = acclist;
GridView1.DataBind();
}
protected void Retrieve_Attendance_Click(object sender, EventArgs e)
{
string _connStr = ConfigurationManager.ConnectionStrings["HealthDBContext"].ConnectionString;
SqlConnection SQLConn = new SqlConnection(_connStr);
/* string username = Session["User"].ToString();*/
SqlCommand cmd = new SqlCommand("SELECT * FROM Student WHERE ClassCode = #ClassCode", SQLConn);
SQLConn.Open();
cmd.Parameters.AddWithValue("#ClassCode", tb_classcode.Text);
cmd.ExecuteNonQuery();
SQLConn.Close();
SqlDataAdapter SQLAdapter = new SqlDataAdapter(cmd);
DataTable DT = new DataTable();
SQLAdapter.Fill(DT);
GridView1.DataSource = DT;
GridView1.DataBind();
}
protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
{
int result = 0;
Student stud = new Student();
string categoryID = GridView1.DataKeys[e.RowIndex].Value.ToString();
result = stud.AccountDelete(categoryID);
if (result > 0)
{
Response.Write("<script>alert('Student Remove successfully');</script>");
}
else
{
Response.Write("<script>alert('Student Removal NOT successfully');</script>");
}
Response.Redirect("AssignmentAttendance.aspx");
}
protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
GridView1.EditIndex = e.NewEditIndex;
bind();
}
protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
{
GridView1.EditIndex = -1;
bind();
}
protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
int result = 0;
Student stud = new Student();
GridViewRow row = (GridViewRow)GridView1.Rows[e.RowIndex];
string tStudent_ID = ((TextBox)row.Cells[0].Controls[0]).Text;
string tClassCode = ((TextBox)row.Cells[3].Controls[0]).Text;
result = stud.AttendanceUpdate(tClassCode, tStudent_ID);
/*if (result > 0)
{
Response.Write("<script>alert('Product updated successfully');</script>");
}
else
{
Response.Write("<script>alert('Product NOT updated');</script>");
}*/
GridView1.EditIndex = -1;
bind();
}
}
}
Above is my AssignmentAttendance.aspx.cs code
<%# Page Title="" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="AssignmentAttendance.aspx.cs" Inherits="Lab06.AssignmentAttendance" %>
<asp:Content ID="Content1" ContentPlaceHolderID="HeadContent" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<p>
Attendance</p>
<p>
Filter Search</p>
<p>
Class code <asp:TextBox ID="tb_classcode" runat="server"></asp:TextBox>
</p>
<p>
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" Height="168px" Width="1451px" OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowDeleting="GridView1_RowDeleting" OnRowEditing="GridView1_RowEditing" OnRowUpdating="GridView1_RowUpdating">
<Columns>
<asp:BoundField AccessibleHeaderText="Joe" DataField="Student_ID" HeaderText="Student_ID" />
<asp:BoundField AccessibleHeaderText="Joe" DataField="Name" HeaderText="Name" />
<asp:BoundField AccessibleHeaderText="Joe" DataField="Pass" HeaderText="Pass" />
<asp:BoundField DataField="ClassCode" HeaderText="ClassCode" />
<asp:CommandField AccessibleHeaderText="Joe" ShowDeleteButton="True" ShowEditButton="True" />
</Columns>
</asp:GridView>
</p>
<asp:Button ID="Retrieve_Attendance" runat="server" Text="Confirm" style="float:right;" OnClick="Retrieve_Attendance_Click" />
</asp:Content>
Above is my AssignmentAttendance.aspx codes
My normal retrieve works however, when I click on the update button, it will not update the current data it has in the gridview but in fact retrieve all the data from the db and display it into the grid view.
My normal retrieve
My gridview after pressing update
Anyone know why this happens?