我應該如何在我的 Flutter 應用程序中使用 FirebaseAuth.instance.onAuthStateChanged？

Question

在我的 flutter 應用程序中，我嘗試使用 Provider 包中的 ChangeNotifier 將 Firebase 用戶對象傳遞給降序小部件。 我的第一個想法是在 StreamBuilder 中這樣做：

  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;
      },
    );
  }

唯一的問題是，顯然構建器函數在構建主體小部件時異步運行，因此狀態同時被標記為臟。 有沒有更聰明的方法將 FirebaseUser 傳遞給降序小部件樹？

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

所以這個問題的答案是你不應該使用 StreamBuilder 而應該使用監聽器。

  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;
  }