In Flutter, navigating to a page that have a heavy widget is too slow in an old device environmnet

Question

I'd like to implement Survey Platform

A survey has many questions and each of them has a part (ex. Part1, Part2, and so on...)

Each part is displayed in one page. (One page equals to one page)

After user finished the survey, they could check the result in one page. That page has a SingleChildScrollView and the SingleChildScrollView contains all of the question's answers. (This is a client's request, so it could not be revised)

Also, I have selected GetX library to administrate State and used RxDart to manage async.

At the onInit method in a answers page's controller, I call the result api and save it to RxList variable.

In answers page's view, if the RxList variable's value is null, it builds CircularProgressIndicator. And in a case of not null, it builds SingleChildScrollView.

I'd like to make the answers page right away pop up when the Get.toNamed method is called and the CircularProgressIndicator has been displayed until the RxList variable is initialized.

But, when I called the Get.toNamed method, the screen had been stoped in the page that called Get.toNamed method. And a few seconds later, the answers page finally pop up.

What should I do to solve this problem?? My code is like belows.

// Survey Answers View
class SurveyResultDetailView extends BaseView<SurveyResultDetailController> {
  @override
  PreferredSizeWidget? appBar(BuildContext context) {
  @override
  Widget body(BuildContext context) {
    return Obx(
      () {
        if (controller.surveyDiagnosisUiModel == null) {
          return CircularProgressIndicator();
        }

        return SingleChildScrollView(
          child: Column(
            children: [
              So long childrens~~~
            ],
          ),
        );
      }
    );
  }
}

// Survey Answers Controller
class SurveyResultDetailController extends BaseController {
  final PreferenceManager _preferenceManager =
      Get.find(tag: (PreferenceManager).toString());

  late final String surveyConfigId;

  final Rxn<SurveyDiagnosisResultUiModel> _rxModel =
      Rxn<SurveyDiagnosisResultUiModel>(null);

  SurveyDiagnosisResultUiModel? get surveyDiagnosisUiModel => _rxModel.value;

  void setSurveyDiagnosisUiModel(SurveyDiagnosisResultUiModel? value) {
    _rxModel.value = value;
  }

  final RxList<SurveyQuestionListUiModel> _surveyQuestionListUiModel =
      RxList<SurveyQuestionListUiModel>();

  List<SurveyQuestionListUiModel> get surveyQuestionListUiModel =>
      _surveyQuestionListUiModel.toList();

  void getDiagnosisResultUiModel() {
    Future<String> diagnosisResultFuture =
        _preferenceManager.getString('recent_detail_result');

    callDataService(
      diagnosisResultFuture,
      onSuccess: _handleDiagnosisResultResponseSuccess,
    );
  }

  void _handleDiagnosisResultResponseSuccess(String response) {
    ~~~~~ response entity mapping to ui model code

    _surveyQuestionListUiModel.refresh();
  }

  List<SurveyQuestionListUiModel> parseQuestionListByPartNumber(int number) {
    return surveyQuestionListUiModel
        .where((element) => element.partNumber == number)
        .toList();
  }

  /// ------------> 생애설계 행동 진단 결과 관련 값

  @override
  void onInit() {
    surveyConfigId = Get.arguments as String;
    getDiagnosisResultUiModel();
    super.onInit();
  }
}