GridView with Paging, Sorting, Update, Delete, Searching

using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;

public partial class ShowData : System.Web.UI.Page
{
    Connection con = new Connection();
    DataTable dtable;
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            fillgrid();
            Session.Add("ope", "Listing");
        }
    }
    protected void fillgrid()
    {
        string query = "select * from test_reg";
        dtable = con.sqlSelect(query);
        grdList.DataSource = dtable;
        grdList.DataBind();
    }
    public string getImage(string Photo)
    {
        string varimg = "~/Image/";
        varimg += Photo;
        return varimg;
    }
    protected void grdList_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        grdList.PageIndex = e.NewPageIndex;
        fillgrid();
    }
    protected void grdList_Sorting(object sender, GridViewSortEventArgs e)
    {
        string query = "select * from test_reg";
        dtable = con.sqlSelect(query);
        Session["sort"] = e.SortExpression;
        string sortstr = Session["sort"].ToString();
        DataView dview = new DataView(dtable);
        if (sortstr == "asc")
            dview.Sort = e.SortExpression + " desc";
        else
            dview.Sort = e.SortExpression + " asc";

        grdList.DataSource = dview;
        grdList.DataBind();
    }
    protected void grdList_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
        int uid = Convert.ToInt32(grdList.DataKeys[e.RowIndex].Values[0]);       
        con.sql_delete_data(uid);
        fillgrid();
    }
    protected void ImageButton3_Click(object sender, ImageClickEventArgs e)
    {
        Session.Add("ope", "Listing");
        if (TextBox1.Text != "")
        {
            string query = "select * from test_reg where Id=" + TextBox1.Text;
            dtable = con.sqlSelect(query);
            grdList.DataSource = dtable;
            grdList.DataBind();
            TextBox1.Text = "";
        }
        else
        {
            string query = "select * from test_reg";
            dtable = con.sqlSelect(query);
            grdList.DataSource = dtable;
            grdList.DataBind();
        }
    }
    protected void grdList_RowEditing(object sender, GridViewEditEventArgs e)
    {
        int test_reg_Id = Convert.ToInt32(grdList.DataKeys[e.NewEditIndex].Values[0]);
        Session.Add("ope", "Edit");
        Session.Add("test_reg_Id", test_reg_Id);
        Response.Redirect("newuser.aspx");
    }
    protected void logout_Click(object sender, EventArgs e)
    {
       Response.Write("<script language=javascript> window.open('Login.aspx','_parent',replace=false);  

       </script>");
       Session["name"] = null;
    }
}