asp.Netバックグラウンドポップアップダイアログ

protected void btnCallBack_Click(object sender, EventArgs e)
    {
        //do sth
        string js = string.Format("document.getElementById('{0}').value=confirm('    ?');document.getElementById('{1}').click();", hid.ClientID,btnHid.ClientID);
        ClientScript.RegisterStartupScript(GetType(), "confirm", js, true);
    }
    protected void btnHid_Click(object sender, EventArgs e)
    {
        string result = hid.Value.ToLower() == "true" ? " " : " ";
        Response.Write(string.Format("     {0}",result));
    }