private async void btnDownload_Click(object sender, EventArgs e)
        {
            try
            {
                if (!IsOnline())
                {
                    throw new Exception("Brak połączenia z internetem");
                }

                ShowMessageAndStart("Pobieram bazę danych");
                FindViewById <Button>(Resource.Id.btnDownload).Visibility = ViewStates.Gone;
                DictionaryXMLHelper dictionaryXMLHelper = new DictionaryXMLHelper();
                xml_doc = await dictionaryXMLHelper.DownloadDictionary(db_remote_info.file_link);

                ShowMessageAndStart("Synchronizuję bazę danych");
                FindViewById <Button>(Resource.Id.btnDeleteTables).Visibility = ViewStates.Gone;
                dictionaryDBHelper_import = new DictionaryDBHelper();
                dictionaryDBHelper_import.BeforeSynchro();
                foreach (XmlNode xml_category in xml_doc.SelectSingleNode("dictionary").SelectNodes("category"))
                {
                    AddCategory(null, (XmlElement)xml_category);
                }
                dictionaryDBHelper_import.SetVersion(db_remote_info.version);
                dictionaryDBHelper_import.AfterSynchro();
                ShowMessageAndStop(string.Format("Baza została zsynchronizowana"));
                FindViewById <Button>(Resource.Id.btnCheckVersion).Visibility = ViewStates.Gone;
                FindViewById <Button>(Resource.Id.btnDownload).Visibility     = ViewStates.Gone;
            }
            catch (Exception ex)
            {
                FindViewById <Button>(Resource.Id.btnDownload).Visibility = ViewStates.Visible;
                ShowError(ex.Message);
            }
        }