Flutter + Firebase Throwing Unhandled Exception: This widget has been unmounted Error Using Navigato

Posted 2023-02-23

【中文标题】Flutter + Firebase Throwing Unhandled Exception: This widget has been unmounted Error Using Navigator to change view

【英文标题】：

【发布时间】：2021-06-27 23:52:00

【问题描述】：

我有一个由 firebase 驱动的 Flutter 应用程序，该应用程序正在运行，但出现错误。

正如我所料，当应用程序打开时，用户必须使用电子邮件和密码登录，如果登录成功，他们会看到一个名为 WelcomeScreen 的新视图。

发生了什么，用户在登录后被带到欢迎屏幕，但我收到以下错误

[VERBOSE-2:ui_dart_state.cc(186)] Unhandled Exception: This widget has been unmounted, so the State no longer has a context (and should be considered defunct).
Consider canceling any active work during "dispose" or using the "mounted" getter to determine if the State is still active.
#0      State.context.<anonymous closure> (package:flutter/src/widgets/framework.dart:1088:9)
#1      State.context (package:flutter/src/widgets/framework.dart:1094:6)
#2      _AuthScreenState.initState.<anonymous closure> (package:autos_latinos/screens/auth_screen.dart:81:35)
#3      _rootRunUnary (dart:async/zone.dart:1362:47)
#4      _CustomZone.runUnary (dart:async/zone.dart:1265:19)
#5      _CustomZone.runUnaryGuarded (dart:async/zone.dart:1170:7)
#6      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:341:11)
#7      _DelayedData.perform (dart:async/stream_impl.dart:591:14)
#8      _StreamImplEvents.handleNext (dart:async/stream_impl.dart:706:11)
#9      _PendingEvents.schedule.<anonymous closur<…>

它似乎指向我的代码中的这一部分，我用它来跟踪来自 firebase 的 authStateChanges：

FirebaseAuth.instance.authStateChanges().listen((User user) 
      if (user == null) 
        print('User is currently signed out!');
        if(AuthScreen.id != '/AuthScreen')
          Navigator.pushReplacement(context, MaterialPageRoute(builder: (BuildContext context) => AuthScreen()));
        else
          print("Already on auth screen");
        


       else 
        //Send to welcome screen
        print('User is signed in!');
        Navigator.pushReplacement(context, MaterialPageRoute(builder: (BuildContext context) => WelcomeScreen()));
      
    );

非常感谢任何有关如何防止此错误的建议。

【问题讨论】：

您好，您找到解决方案了吗？我需要在我的代码中解决这个问题。

【参考方案1】：

您必须像这样在有状态小部件的dispose 方法中配置监听器：

class Sample extends StatefulWidget 
  @override
  _SampleState createState() => _SampleState();


class _SampleState extends State<Sample> 
  StreamSubscription<User> _listener;

  @override
  Widget build(BuildContext context) 
    return Container();
  

  @override
  void initState() 
    _listener = FirebaseAuth.instance.authStateChanges().listen((User user) 
      if (user == null) 
        print('User is currently signed out!');
        if (AuthScreen.id != '/AuthScreen') 
          Navigator.pushReplacement(
              context,
              MaterialPageRoute(
                  builder: (BuildContext context) => AuthScreen()));
         else 
          print("Already on auth screen");
        
       else 
        //Send to welcome screen
        print('User is signed in!');
        Navigator.pushReplacement(
            context,
            MaterialPageRoute(
                builder: (BuildContext context) => WelcomeScreen()));
      
    );
    super.initState();
  

  @override
  void dispose() 
    _listener.cancel();
    super.dispose();
  

【讨论】：

我试了一下，但它仍然给我以下错误[VERBOSE-2:ui_dart_state.cc(186)] Unhandled Exception: setState() called after dispose(): _LoginCardState#bf03a(lifecycle state: defunct, not mounted, tickers: tracking 0 tickers)