firebase - 我应该如何在Flutter应用中使用FirebaseAuth.instance.onAuthStateChanged？

Question

在我的flutter应用程序中，我尝试使用Provider包中的ChangeNotifier将Firebase用户对象传递给降序的小部件。我的第一个想法是在StreamBuilder中执行以下操作:

  Widget _authBuilder(context, Widget body) {
    final authModel = Provider.of<FAAuthModel>(context);


    return StreamBuilder(
      stream: FirebaseAuth.instance.onAuthStateChanged,
      builder: (context, snapshot) {

        authModel.user = snapshot.data;

        return body;
      },
    );
  }

唯一的问题是，显然，构建器函数在构建主体窗口小部件时异步运行，因此状态同时被标记为脏。是否有将FirebaseUser传递到降序小部件树的更智能方法？

I/flutter (28504): ══╡ EXCEPTION CAUGHT BY FOUNDATION LIBRARY ╞════════════════════════════════════════════════════════
I/flutter (28504): The following assertion was thrown while dispatching notifications for FAAuthModel:
I/flutter (28504): setState() or markNeedsBuild() called during build.
I/flutter (28504): This _DefaultInheritedProviderScope<FAAuthModel> widget cannot be marked as needing to build because
I/flutter (28504): the framework is already in the process of building widgets.  A widget can be marked as needing to
I/flutter (28504): be built during the build phase only if one of its ancestors is currently building. This exception
I/flutter (28504): is allowed because the framework builds parent widgets before children, which means a dirty
I/flutter (28504): descendant will always be built. Otherwise, the framework might not visit this widget during this
I/flutter (28504): build phase.
I/flutter (28504): The widget on which setState() or markNeedsBuild() was called was:
I/flutter (28504):   _DefaultInheritedProviderScope<FAAuthModel>
I/flutter (28504): The widget which was currently being built when the offending call was made was:
I/flutter (28504):   StreamBuilder<FirebaseUser>
I/flutter (28504): 

Answer 1

因此，此问题的答案是您不应使用StreamBuilder，而应使用侦听器。

  Widget _authBuilder(context, Widget body) {
    Stream<FirebaseUser> stream;
    final authModel = Provider.of<FAAuthModel>(context);

    stream = FirebaseAuth.instance.onAuthStateChanged;

    stream.listen((snapshot) {

      /* We are not logged in */
      if (snapshot == null && authModel.user == null) {
         //Do nothing
      }
      /* We are not logged in, or we are logging out */
      else if (snapshot == null) {
        authModel.user = null;
        /* We are logged in but we just opened our app */
      } else if (authModel.user == null) {
        authModel.user = snapshot;
        /* We are logged in but something happened e.g. the widget tree was rebuilt and we just logged out? */
      } else if (authModel.user.uid != snapshot.uid) {
        authModel.user = snapshot;
      }
    });

    return body;
  }