private void onSubmit(object obj) { user.Username = username; user.Password = password; List <User> allUsers = _validateUserService.getAllUsers(); if (_validateUserService.ValidateUser(allUsers, user)) { _navigation.NavigateAsync(nameof(AllToddlersView)); } else { App.Current.MainPage.DisplayAlert("Failed login", "Not Authorized", "Ok"); _navigation.NavigateAsync(nameof(LoginView)); } }