下拉列表的AutoPostBack没有加载最近更改的值

下面是我的下拉列表（drpdwnshowitems）的Page_Load和SelectedIndexChanged事件的代码，在该事件中，我从数据库绑定了数据，并且有AutoPostBack true，因为我需要这样做。我将最近选择的值（item）存储到名为"NoOfShowItem"的cookie中，我在页面加载中请求该值并希望使用，但它只提供以前的值。为了看到这一点，我还在javascript消息框中显示了同样的值。在一步一步执行之后，我看到selectedIndexChanged事件在加载（Postback）页面后被触发。我找了很多，但找不到确切的解决方案。所以请帮帮我。提前感谢。

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI; 
using System.Web.UI.WebControls;
using System.Data;
public partial class Client_Category : System.Web.UI.Page
{
float countshowitem;
protected void Page_Load(object sender, EventArgs e)
{
//to see recently selected value
Response.Write("<script language='"javascript'">alert('"+
drpdwnshowitems.SelectedValue + "')</script>");
if (!IsPostBack)
    {
        DataTable dtno = ShowItemsFunctions.Select_All_Numbers();
        DataRow dr = dtno.NewRow();
        dr["NoOfProduct"] = "--Select One--";
        dtno.Rows.InsertAt(dr, 0);
        drpdwnshowitems.DataSource = dtno;
        drpdwnshowitems.DataTextField = "NoOfProduct";
        drpdwnshowitems.DataValueField = "NoOfProduct";
        drpdwnshowitems.DataBind();
    }
    try
   {
     countshowitem = float.Parse(Request.Cookies["NoOfShowItem"].Value.ToString());
     drpdwnshowitems.SelectedValue = countshowitem.ToString();
    }
    catch (Exception ex)
    {
       countshowitem = 9;
       drpdwnshowitems.SelectedValue = countshowitem.ToString();
    }
}
protected void drpdwnshowitems_SelectedIndexChanged(object sender, EventArgs e)
{
    countshowitem = int.Parse(drpdwnshowitems.SelectedValue.ToString());
    Response.Cookies["NoOfShowItem"].Value = drpdwnshowitems.SelectedValue.ToString();
    Response.Cookies["NoOfShowItem"].Expires = System.DateTime.Now.AddHours(2);
}
}

drpdwnshowitems.SelectedIndexChanged += drpdwnshowitems_SelectedIndexChanged;