user control Ispostback is always true after page refresh in asp.net and c#(how to solve)

private bool PageRefresh
    {
        get { return (bool)(Session["PageRefresh"] ?? false); }
        set { Session["PageRefresh"] = value; }
    }

void Page_PreRender(object obj, EventArgs e)
    {
        ViewState["PageRefresh"] = Session["PageRefresh"];
    }

protected void Page_Load(object sender, EventArgs e)
    {
      
        if (!IsPostBack)
        {
            Session["PageRefresh"] = Server.UrlEncode(System.DateTime.Now.ToString());
         }
   
      //and other code

}

protected void btnAction1_Click(object sender, ImageClickEventArgs e)
    {
        /// </summary>

        if (Session["PageRefresh"].ToString() == ViewState["PageRefresh"].ToString())
        {

                    //code of Action1

        }

        Session["PageRefresh"] = Server.UrlEncode(System.DateTime.Now.ToString());

}