flutter - 在空 flutter 上调用 setter/getter 'loadingStatus'

Question

嗨
我在 flutter 中有错误
它只是从提供程序获取加载状态，在我使用的所有提供程序中都有相同的错误

The getter 'loadingStatus' was called on null flutter

This error appears only in console but app works fine -_-

class _DoctorInfoPageState extends State<DoctorInfoPage> {
  GeneralService _generalService;
  ProfileService _profileService;
  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
      _generalService = Provider.of<GeneralService>(context);
      _profileService = Provider.of<ProfileService>(context);
      loadingReviews();
    });
  }

  loadingReviews() async {
    _generalService.setLoadingState(true);
    await _profileService.getReviews(context);
    _generalService.setLoadingState(false);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        elevation: 0.0,
        centerTitle: true,
        backgroundColor: Colors.white,
        leading: IconButton(
          icon:
              Icon(Icons.chevron_left, size: 30, color: Const.appMainBlueColor),
          onPressed: () {
            print('test');
          },
        ),
        title: Text(
          "Doctor Info",
          style: TextStyle(
              color: Const.appMainBlueColor,
              fontWeight: FontWeight.w600,
              fontSize: 18),
        ),
      ),
      body: _generalService.loadingStatus != null &&
              _generalService.loadingStatus
          ? Center(child: PumpHeart(size: 35.0))
          : SafeArea()
);
  }
}

我尝试了越来越多，但是什么也没有改变，所以一个 Ant 可以告诉我错误在哪里吗？
这是提供者代码

class GeneralService with ChangeNotifier {
  bool _isLoading = false;

  // Change Loading Status
  void setLoadingState(bool value) {
    _isLoading = value;
    notifyListeners();
  }

  // Get Loading Status
  bool get loadingStatus => _isLoading;

}

Answer 1

WidgetsBinding.instance.addPostFrameCallback将在以后的一帧中被调用(作为下一帧的Future)，因为构建_generalService.loadingStatus _generalService的第一帧尚未被引用(您正在校准null.loadingStatus)。如果您想保留该逻辑，只需将其更改为_generalService?.loadingStatus != null && _generalService.loadingStatus我不知道您的类(class)，但将GeneralService改成ProxyProvider的ProfileService或FutureProvider的_profileService.getReviews(context)也许会更好，但这是您面临的问题的一部分