private async void Button_Clicked(object sender, EventArgs e)
        {
            if (entryUserName.Text == "" || entryPassword.Text == "")
            {
                await DisplayAlert("Attenzione", "Completare tutti i campi!", "Ok.");
            }
            else
            {
                busyindicator.IsBusy    = true;
                busyindicator.IsVisible = true;
                BtnLogin.IsVisible      = false;
                z.organizzazioneScelta();
                try
                {
                    access = await z.login();
                }
                catch (Exception)
                {
                    await DisplayAlert("Attenzione", "Connessione non riuscita", "Riprova!");

                    busyindicator.IsBusy    = false;
                    busyindicator.IsVisible = false;
                    BtnLogin.IsVisible      = true;
                }
                if (access)
                {
                    App.Current.MainPage    = new NavigationPage(new MainPage());
                    busyindicator.IsBusy    = false;
                    busyindicator.IsVisible = false;
                    BtnLogin.IsVisible      = true;
                }
                else
                {
                    busyindicator.IsBusy    = false;
                    busyindicator.IsVisible = false;
                    BtnLogin.IsVisible      = true;
                }
            }
        }