File Download from Gridview in asp.net with C#

Downloads.aspx

<asp:GridView ID="gvDownloads"  runat="server" AutoGenerateColumns="False">
            <Columns>
 <asp:TemplateField HeaderText="Brochures" HeaderStyle-BackColor="Gainsboro">
            <ItemTemplate>
           
             <asp:Label ID="lblfile" width="400px"  Text='<%#DataBinder.Eval(Container.DataItem,"filename") %>' runat="server"></asp:Label>
                           
                              <asp:HyperLink ID="HyperLink1"   runat="server"  NavigateUrl='<%# Eval("id", "~/Download.aspx?id={0}") %>'
                              Text="Download"></asp:HyperLink>
                           
              <asp:HyperLink ID="lnkView" runat="server"    NavigateUrl='<%# Eval("id", "~/View.aspx?id={0}") %>' Text="View"></asp:HyperLink>

            </ItemTemplate>
          </asp:TemplateField>
            </Columns>
            </asp:GridView>


Downloads.aspx.cs





  public void display()
    {
        if (con.State == ConnectionState.Closed)
        {
            con.Open();
        }
        DataSet ds = new DataSet();
        SqlDataAdapter da = new SqlDataAdapter("select * from downloads", con);
        da.Fill(ds);
        gvDownloads.DataSource = ds;
        gvDownloads.DataBind();
        con.Close();
    }


Download.aspx.cs



using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Net;
using System.Web.Mail;
using System.IO;

public partial class Download : System.Web.UI.Page
{
    public SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["SLMFConnection"].ToString());
    public string conStr = ConfigurationManager.ConnectionStrings["SLMFConnection"].ToString();
    SqlCommand cmd;
    int cid;
 
    byte[] b;
    protected void Page_Load(object sender, EventArgs e)
    {
        int docId = Convert.ToInt32(Request.QueryString["id"]);
        if (con.State == ConnectionState.Closed)
        {
            con.Open();
        }
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandText = "Select * from downloads where id = @id";
        cmd.Parameters.Add("@id", SqlDbType.Int);
        cmd.Parameters[0].Value = docId;
        SqlDataReader dr = cmd.ExecuteReader();

        if (dr.Read())
        {
            b = ((byte[])(dr["contentfile"]));
            Response.Clear();
            Response.ContentType = dr["contenttype"].ToString();
            Response.AppendHeader("Content-Disposition", ("attachment; filename=\""
                       + (dr["filename"] + "\"")));
            Response.BinaryWrite(b);
        }
        con.Close();
    }
}