Dynamically setting Postback Trigger For the UpdatePanel in Master Page

protected void Page_Init(object sender, EventArgs e)
        {
            PostBackTrigger trigger = new PostBackTrigger();
            trigger.ControlID = btn_export.UniqueID;
            UpdatePanel pnl = (UpdatePanel)Page.Master.FindControl("pnlData");

            //pnldata is the master page UpdatePanel Id.
            pnl.Triggers.Add(trigger);
        }