Disable form repost on browser refresh

Here's a trick I found to prevent a form repost on browser refresh

        protected void Page_PreRender(object sender, EventArgs e)

        {

                     ViewState["Check_Page_Refresh"] = Session["Check_Page_Refresh"];

        }

        protected void Page_Load(object sender, EventArgs e)

        {

            if (!IsPostBack)

            {

                Session["Check_Page_Refresh"] = DateTime.Now.ToString();

            }

        }

protected void btn_Click(object sender, EventArgs e)

{

if (ViewState["Check_Page_Refresh"].ToString() == Session["Check_Page_Refresh"].ToString())

{

     <your main code you want to execute once on button click here>

}

}