string html;
            string url = "http://clarasys.cz/android/login.php?user=" + textBox1.Text + "&pass=" + textBox2.Text;
            using (WebClient wc = new WebClient())
            {
                html = wc.DownloadString(url);
            }

            if(html == "chybné údaje"){

                bp.Text = "Chyba!";

            }