如何使用Flutter中的提供程序正确获取API

Question

我目前正在处理一个问题，我需要一些API中的数据才能将其显示在我的小部件中。我遵循了一些提供程序体系结构模式，在其中两次setState：

1-获取数据时

2-当已经获取数据时

所以我当前正在处理的问题是，我的小部件引发以下错误：

setState() or markNeedsBuild() called during build.

我知道此错误是因为在构建过程中调用了setState，但是..如何在构建过程中获取我的api，然后将其显示给我的小部件？这是我的代码：

NewsPage.dart

    class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  SideBarWidget _sidebar;

  @override
  void initState() {
    Provider.of<HomeViewModel>(context, listen: false)
        .fetchUltimaNoticia(context); --> ****Data to get fetched****
    _sidebar = const SideBarWidget();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('INICIO'),
        centerTitle: true,
        automaticallyImplyLeading: false,
        leading: Builder(
          builder: (context) => IconButton(
            icon: const Icon(Icons.menu),
            onPressed: () => Scaffold.of(context).openDrawer(),
          ),
        ),
      ),
      drawer: _sidebar,
      body: FormNoticiaContainer(),
    );
  }
}

FormContainer（）

Widget build(BuildContext context) {
    return _crearBodyNoticia(context);
  }

  Widget _crearBodyNoticia(context) {
    final homeVm = Provider.of<HomeViewModel>(context, listen: true);
    return homeVm.state == ViewState.Busy
        ? Center(child: CircularLoading())
        : Center(
            child: DataToShowWidget()

HomeViewModel.dart

    class HomeViewModel extends BaseModel {
  ////////
  //NOTICIAS
  ////////

  NoticiaDB _noticia;

  NoticiaDB get noticia => _noticia;

  set setNoticia(NoticiaDB noticia) {
    _noticia = noticia;
  }

  Future fetchUltimaNoticia(BuildContext context) async {
    setState(ViewState.Busy);

    var response = await noticiaProvider.obtenerNoticiaPublicada();

    setNoticia = response;

    setState(ViewState.Idle);
  }
}

BaseModel

 ViewState _state = ViewState.Idle;

  ViewState get state => _state;

  void setState(ViewState viewState) {
    _state = viewState;
    notifyListeners();
  }

Answer 1

您可以使用WidgetsBinding.instance.addPostFrameCallback有关详细信息，您可以参考https://www.didierboelens.com/faq/week2/

代码段

@override
void initState(){
  super.initState();
  WidgetsBinding.instance.addPostFrameCallback((_){
    Provider.of<HomeViewModel>(context, listen: false)
    .fetchUltimaNoticia(context);  

  });
}