i created dynamic label, hyperlink and a button...but button click is not firing

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Configuration;
using System.Data;
using System.IO;
using System.Collections;
using System.Text;

namespace WebApplication7
{
    public partial class viewad1 : System.Web.UI.Page
    {
        public string adv;
        public string usr;
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                FillDropDownList();
                FillDropDownList1();     
            }
          
            
            
        }

        protected void FillDropDownList()
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["sampledbConnectionString"].ConnectionString);
            conn.Open();

            DataSet ds = new DataSet();
            SqlDataAdapter myda = new SqlDataAdapter("Select * FROM category", conn);
            myda.Fill(ds);
            conn.Close();
            catddlist.DataSource = ds;
            catddlist.DataTextField = "category_name";
            catddlist.DataValueField = "category_id";
            catddlist.DataBind();
            catddlist.Items.Insert(0, new ListItem("Select", "0"));
            subcatlist.Items.Insert(0, new ListItem("Select", "0"));
            
        }

        
        protected void FillDropDownList1()
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["sampledbConnectionString"].ConnectionString);
            conn.Open();

            DataSet ds = new DataSet();
            SqlDataAdapter myda = new SqlDataAdapter("Select * FROM places", conn);
            myda.Fill(ds);
            conn.Close();
           citylist.DataSource = ds;
            citylist.DataTextField = "cityname";
            citylist.DataValueField = "city";
            citylist.DataBind();
            citylist.Items.Insert(0, new ListItem("Select", "0"));
            }

        //Double click on Company`s DropDown.;


        protected void catddlist_SelectedIndexChanged(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["sampledbConnectionString"].ConnectionString);
            conn.Open();

            int catid = Convert.ToInt32(catddlist.SelectedValue);
            DataSet ds = new DataSet();
            SqlDataAdapter myda = new SqlDataAdapter("Select subcategory_id,subcategoryname FROM subcategory where category_id=" + catid, conn);
            myda.Fill(ds);
            conn.Close();
            subcatlist.DataSource = ds;
            subcatlist.DataTextField = "subcategoryname";
            subcatlist.DataValueField = "subcategory_id";
            subcatlist.DataBind();
            subcatlist.Items.Insert(0, new ListItem("select", "0"));
        }

        protected void FillPage1()
        {
            ArrayList adlist = new ArrayList();
            string sub = subcatlist.SelectedValue.ToString();
            string cit = null;
            adlist = conclass1.getadbycat(sub, cit);

            Panel linkpanel = new Panel();
                
           
            int a = 0;
            foreach (adclass ad in adlist)
            {
                Label op = new Label();
                StringBuilder sb = new StringBuilder();
                HyperLink link = new HyperLink();

                sb.Append(
                    string.Format(
                        @"<table class="adtable">
            <tr>
                <th rowspan="6" width="150px"><img  runat="server" src='{6}' /></th>
                <th width="50px">Title: 
                <table><tbody><tr><table><tbody><tr><td>{1}</td></tr></tbody></table></tr></tbody></table>
            </th></tr>
            <tr>
                <th>Id: </th>
                <td>{0}</td>
            </tr>
<tr>
                <th>Price: </th>
                <td>{2} Rs</td>
            </tr>

            <tr>
                <th>Type: </th>
                <td>{3}</td>
            </tr>

            <tr>
                <th>Description: </th>
                <td>{4}</td>
            </tr>
            <tr>
                <th>Posted by: </th>
                <td>{5}</td>
            </tr>
            <tr>
                <td colspan="2">{5}</td>
            </tr>           
            
           </table> 
 ", ad.product_id, ad.title, ad.price, ad.type, ad.description, ad.email_username, ad.imagepath));


                if (sb.ToString() != "")
                    op.Text = sb.ToString();

                else
                    op.Text = "No Results";




                link.Text = "View ad";
                link.NavigateUrl = "~/userpage.aspx";

                linkpanel.Controls.Add(op);
                linkpanel.Controls.Add(link);
            }


            panelop.Controls.Add(linkpanel);
        }
            protected void FillPage()
        {   
            ArrayList adlist = new ArrayList();
            string sub = subcatlist.SelectedValue.ToString();
            string cit = citylist.SelectedValue.ToString();
            adlist = conclass1.getadbycat(sub,cit);
            int a = 0;
            Panel linkpanel = new Panel();
            foreach (adclass ad in adlist)
            {
               
                Label op = new Label();
                
                StringBuilder sb = new StringBuilder();
                Button viewbutton = new Button();
                adv = ad.product_id.ToString();
                usr=ad.email_username.ToString();
               sb.Append(
                    string.Format(
                        @"<table class="adtable">
            <tr>
                <th rowspan="6" width="150px"><img  runat="server" src='{6}' /></th>
                <th width="50px">Title: 
                <table><tbody><tr><table><tbody><tr><td>{1}</td></tr></tbody></table></tr></tbody></table>
            </th></tr>
            <tr>
                <th>Id: </th>
                <td>{0}</td>
            </tr>
<tr>
                <th>Price: </th>
                <td>{2} Rs</td>
            </tr>

            <tr>
                <th>Type: </th>
                <td>{3}</td>
            </tr>

            <tr>
                <th>Description: </th>
                <td>{4}</td>
            </tr>
            <tr>
                <th>Posted by: </th>
                <td>{5}</td>
            </tr>
            <tr>
                <td colspan="2">{5}</td>
            </tr>           
            
           </table> 
 ", ad.product_id, ad.title, ad.price, ad.type, ad.description, ad.email_username, ad.imagepath));
 
            if (sb.ToString() != "")
                op.Text = sb.ToString();

            else
                op.Text = "No Results";




            viewbutton.Text = "View Ad";
            viewbutton.Click += viewbutton_Click;
               
                
            linkpanel.Controls.Add(op);
            linkpanel.Controls.Add(viewbutton);
            }
            panelop.Controls.Add(linkpanel);
            }
           protected void viewbutton_Click(object sender, EventArgs e )
            {
                
                Response.Redirect("login.aspx");
            }
           
        
            
        protected void subcatlist_SelectedIndexChanged(object sender, EventArgs e)
        {

            FillPage1();
            if(!IsPostBack)
            FillDropDownList1();
            
}

        protected void citylist_SelectedIndexChanged(object sender, EventArgs e)
        {
            FillPage();
        }


      
    }
}