Question

我正在为我的应用程序使用FirebaseAuth和Firestore。

“用户”是一个模型，表示Firestore上的文档，并使用FirebaseUser中的uid为其文档ID。

为了获得“用户”，我必须从FirebaseUser传递uid。

我的想法是设置FirebaseUser的StreamProvider，然后设置另一个User的StreamProvider，以FirebaseUser作为参数。

但是发生错误，我找不到此问题的解决方案，任何建议对我都有很大帮助。

List<SingleChildCloneableWidget> uiConsumableProviders = [
  StreamProvider<FirebaseUser>(
    builder: (context) => Provider.of<LoginNotifier>(context, listen: false).streamFirebaseUser,
  ),
  StreamProvider<User>(
    builder: (context) =>
        Provider.of<UserNotifier>(context, listen: false).streamUser(Provider.of<FirebaseUser>(context)),
  ),
];

I/flutter (15813): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (15813): The following assertion was thrown building InheritedProvider<FirebaseUser>:
I/flutter (15813): inheritFromWidgetOfExactType(InheritedProvider<FirebaseUser>) or inheritFromElement() was called
I/flutter (15813): before BuilderStateDelegate<Stream<User>>.initDelegate() completed.
I/flutter (15813): 
I/flutter (15813): When an inherited widget changes, for example if the value of Theme.of()
I/flutter (15813): changes, its dependent widgets are rebuilt. If the dependent widget's reference
I/flutter (15813): to the inherited widget is in a constructor or an initDelegate() method, then
I/flutter (15813): the rebuilt dependent widget will not reflect the changes in the inherited
I/flutter (15813): widget.
I/flutter (15813): 
I/flutter (15813): Typically references to inherited widgets should occur in widget build()
I/flutter (15813): methods. Alternatively, initialization based on inherited widgets can be placed
I/flutter (15813): in the didChangeDependencies method, which is called after initDelegate and
I/flutter (15813): whenever the dependencies change thereafter.
I/flutter (15813):

Answer 1

您不能在Provider.of内部呼叫builder。

但是您可以使用小部件将Provider.of转换为流，然后在builder的{{1}}中使用该流。

这是一个为您完成的小部件：

StreamProvider

那么您可以做：

class ProviderToStream<T> extends StatefulWidget
    implements SingleChildCloneableWidget {
  const ProviderToStream({Key key, this.builder, this.child}) : super(key: key);

  final ValueWidgetBuilder<Stream<T>> builder;
  final Widget child;

  @override
  _ProviderToStreamState<T> createState() => _ProviderToStreamState<T>();

  @override
  ProviderToStream<T> cloneWithChild(Widget child) {
    return ProviderToStream(
      key: key,
      builder: builder,
      child: child,
    );
  }
}

class _ProviderToStreamState<T> extends State<ProviderToStream> {
  final StreamController<T> controller = StreamController<T>();

  @override
  void dispose() {
    controller.close();
    super.dispose();
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    controller.add(Provider.of<T>(context));
  }

  @override
  Widget build(BuildContext context) {
    return widget.builder(context, controller.stream, widget.child);
  }
}

Answer 2

经过一些解决方法后，我通过将Observable中的rxdart与Provider结合起来解决了问题。像这样：

Stream<User> get userStream {
return Observable(_firebaseAuth.onAuthStateChanged).switchMap((user) {
  if (user != null) {
    return userCollection
        .document(user.uid)
        .snapshots()
        .map((doc) => User.fromDocumentSnapshot(doc))
        .handleError(_catchError);
  } else {
    return Observable<User>.just(null);
  }
});}

外部MultiProvider：

StreamProvider<User>(builder: (context) => Provider.of<FireStoreService>(context, listen: false).userStream,),

希望这将帮助面临相同问题的任何人。

如何设置从另一个StreamProvider获取参数值的StreamProvider？

2 个答案: