async void Handle_Clicked(object sender, System.EventArgs e) { if (Validates.validateBook(identificationEditor.Text, ageEditor.Text, nameEditor.Text)) { if (bookController.availableBook(flight, nameEditor.Text, ageEditor.Text, identificationEditor.Text)) { bookController.createBook(flight, nameEditor.Text, ageEditor.Text, identificationEditor.Text); } else { await App.Current.MainPage.DisplayAlert("Alert", "No chairs available", "OK"); } } else { await App.Current.MainPage.DisplayAlert("Alert", "Fill all fields", "OK"); } }