ไม่ต้องการให้ dropdownlist ทำงานตอนที่ใช้คำสั่ง Response.Redirect มาที่หน้าเพจ

public partial class _Default : System.Web.UI.Page
{

    private bool RunOnce
    {
        get
        {
            if (ViewState["RunOnce"] = null)
                ViewState["RunOnce"] = false;
            return Convert.ToBoolean(ViewState["RunOnce"]);
        }
        set
        {
            ViewState["RunOnce"] = value;
        }
    }

    protected void Page_Load(object sender, EventArgs e)
    {

        
        if (!IsPostBack)
        {
        }

        if (!this.RunOnce)
        {
            this.RunOnce = true;
        }
        else
        {
            //...... ใส่ code ที่นี่
        }
    }
}

using System;
using System.Collections;
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;
using System.Drawing;
using System.Collections.Generic;

namespace Project1
{
    public partial class ViewCourse : System.Web.UI.Page
    {
       
        protected void Page_Load(object sender, EventArgs e)
        {
            if (Session["Staff_User"] == null)
            {
                Page.Response.Redirect("../Login.aspx");
            }
            else
            {
                if (!Page.IsPostBack)
                {
                    if (Request.QueryString["ViewCourseID"] == null)
                    {
                        bindData();
                    }
                }
            }

        }
        public void bindData()
        {
                string _cons = ConfigurationManager.AppSettings["ConnectDB"].ToString();

                SqlConnection _con = new SqlConnection(_cons);

                string _strSelect = "SELECT course_id, course_name_thai FROM course";

                SqlCommand _selectCmd = new SqlCommand(_strSelect, _con);

                SqlDataReader _dr;

                try
                {
                    _con.Open();
                    _dr = _selectCmd.ExecuteReader();

                    if (_dr.HasRows)
                    {
                        ddl_course.DataSource = _dr;
                        ddl_course.DataTextField = "course_name_thai";
                        ddl_course.DataValueField = "course_id";
                        ddl_course.DataBind();
                    }
                    else
                    {

                    }
                }
                finally
                {
                    _con.Close();
                }
        }


        protected void btn_ok_Click(object sender, EventArgs e)
        {
                string viewCourseID = ddl_course.SelectedValue.ToString();
                Page.Response.Redirect("ViewCourse.aspx?ViewCourseID=" + viewCourseID);
        }

    }
}

if (Request.QueryString["ViewCourseID"] == null)
   bindData();
else
{
     string ddlSelectedValue = Request.QueryString["ViewCourseID"].ToString() ;
     foreach ( ListItem myItem in ddl_course.items )
     {
         if (ddlSelectectValue.Equals(myItem.Value))
         {
             myItem.Selected = true ;
             break ;
         }
     }
}