Flutter BLoC : Navigator. 在 build() 方法中弹出 StreamBuilder

Question

我正在遵循 BLoC 模式并订阅流，并对构建方法中的状态变化使用react。加载数据后，我想关闭屏幕。

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Bloc'),
      ),
      body: SafeArea(
        child: StreamBuilder<UserState>(
          stream: _userBloc.user,
          initialData: UserInitState(),
          builder: (context, snapshot) {
            if (snapshot.data is UserInitState) {
              return _buildInit();
            }
            if (snapshot.data is UserDataState) {
              Navigator.pop(context, true);
              return Container();
            }
            if (snapshot.data is UserLoadingState) {
              return _buildLoading();
            }
          },
        ),
      ),
    );
  } 

当我在 build() 方法中执行 Navigator.pop(context, true); 时，我得到:

I/flutter ( 4360): ══╡ EXCEPTION CAUGHT BY ANIMATION LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 4360): The following assertion was thrown while notifying status listeners for AnimationController:
I/flutter ( 4360): setState() or markNeedsBuild() called during build.
I/flutter ( 4360): This Overlay widget cannot be marked as needing to build because the framework is already in the
I/flutter ( 4360): process of building widgets. A widget can be marked as needing to be built during the build phase
I/flutter ( 4360): only if one of its ancestors is currently building. This exception is allowed because the framework
I/flutter ( 4360): builds parent widgets before children, which means a dirty descendant will always be built.
I/flutter ( 4360): Otherwise, the framework might not visit this widget during this build phase.

在 BLoC 模式中处理此类情况的正确方法是什么？

我提出的解决方案之一是开始在 initState() 上收听流。在这种情况下，我需要 broadcast() 我的流，因为我有 2 个订阅者。

有没有更好的解决方案？

Answer 1

我想我已经为您找到了解决方案。 (请检查)

让你的代码看起来像:

Widget build(BuildContext context) {
    // other stuff

    if (snapshot.data is UserDataState) {
      myCallback(() {
        Navigator.pop(context, true);
      });
    }

    // other stuff
}
// after build method (but still in the same class,...) write below method

void myCallback(Function callback) {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      callback();
    });
}

希望对您有所帮助。试试吧，请在这里报告以帮助其他人!

Source (flutter_bloc Login medium article)

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