问题

我正在使用authStateChanges监听器在initState()内更改已登录用户的帐户变量。

```dart
  @override
  void initState() {
    // Firebase userChange listener
    FirebaseAuth.instance.authStateChanges().listen((User? user) {
      if (user == null) {
        setState(() { // 这是第43行
          signedIn = false;
          userImage =
              "https://XXXX.XXXXXXXX.XXX/News-Manager/v03/static/sample_user.png";
          userName = "Guest";
        });
      } else {
        setState(() {
          signedIn = true;
          userImage = user.photoURL!;
          userName = user.displayName!;
        });
      }
    });

    // Google Sign In listener
    googleSignIn.onCurrentUserChanged.listen((GoogleSignInAccount? account) {
        setState(() {
          _currentUser = account;
        });
        if (_currentUser != null) {}
    });

    // 检查用户是否已经登录
    googleSignIn.signInSilently();

    super.initState();
  }

有时（不总是）我会遇到这个错误：

E/flutter ( 5961): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: setState() called after dispose(): _SettingsState#60dee(lifecycle state: defunct, not mounted)
E/flutter ( 5961): This error happens if you call setState() on a State object for a widget that no longer appears in the widget tree (e.g., whose parent widget no longer includes the widget in its build). This error can occur when code calls setState() from a timer or an animation callback.
E/flutter ( 5961): The preferred solution is to cancel the timer or stop listening to the animation in the dispose() callback. Another solution is to check the "mounted" property of this object before calling setState() to ensure the object is still in the tree.
E/flutter ( 5961): This error might indicate a memory leak if setState() is being called because another object is retaining a reference to this State object after it has been removed from the tree. To avoid memory leaks, consider breaking the reference to this object during dispose().
E/flutter ( 5961): #0      State.setState.<anonymous closure> (package:flutter/src/widgets/framework.dart:1103:9)
E/flutter ( 5961): #1      State.setState (package:flutter/src/widgets/framework.dart:1138:6)
E/flutter ( 5961): #2      _SettingsState.initState.<anonymous closure> (package:kutchsetu/screens/Settings.dart:43:9)

最初我以为这是因为Google Sign In会弹出帐户选择窗口导致的。

但实际情况并非如此，因为即使没有帐户选择窗口，也会出现错误。

其他解决方法建议在调用setState()之前使用if(mounted)进行检查，但如果监听器不分配值，因为它不会进入if(mounted)，这将破坏功能。

有人知道authChange监听器中导致这个问题的原因吗？

<details>
<summary>英文:</summary>

I am using authStateChanges listner to change a signedIn user&#39;s account variable inside initState()


```dart
  @override
  void initState() {
    // Firebase userChange listener
    FirebaseAuth.instance.authStateChanges().listen((User? user) {
      if (user == null) {
        setState(() { // This is line no 43
          signedIn = false;
          userImage =
              &quot;https://XXXX.XXXXXXXX.XXX/News-Manager/v03/static/sample_user.png&quot;;
          userName = &quot;Guest&quot;;
        });
      } else {
        setState(() {
          signedIn = true;
          userImage = user.photoURL!;
          userName = user.displayName!;
        });
      }
    });

    // Google Sign In listener
    googleSignIn.onCurrentUserChanged.listen((GoogleSignInAccount? account) {
        setState(() {
          _currentUser = account;
        });
        if (_currentUser != null) {}
    });

    // Check if user is already signed in
    googleSignIn.signInSilently();

    super.initState();
  }

And sometimes (not always) I end up with this error:

E/flutter ( 5961): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: setState() called after dispose(): _SettingsState#60dee(lifecycle state: defunct, not mounted)
E/flutter ( 5961): This error happens if you call setState() on a State object for a widget that no longer appears in the widget tree (e.g., whose parent widget no longer includes the widget in its build). This error can occur when code calls setState() from a timer or an animation callback.
E/flutter ( 5961): The preferred solution is to cancel the timer or stop listening to the animation in the dispose() callback. Another solution is to check the "mounted" property of this object before calling setState() to ensure the object is still in the tree.
E/flutter ( 5961): This error might indicate a memory leak if setState() is being called because another object is retaining a reference to this State object after it has been removed from the tree. To avoid memory leaks, consider breaking the reference to this object during dispose().
E/flutter ( 5961): #0      State.setState.<anonymous closure> (package:flutter/src/widgets/framework.dart:1103:9)
E/flutter ( 5961): #1      State.setState (package:flutter/src/widgets/framework.dart:1138:6)
E/flutter ( 5961): #2      _SettingsState.initState.<anonymous closure> (package:kutchsetu/screens/Settings.dart:43:9)

Initially I thought this happens because Google Sign In opens a popup for account selection.

But this is not the case as error also comes when sign in is done without popup of account selection.

Other solution advice to use if(mounted) before calling setState(), but if listner not assign values as it doesn't go inside if(mounted), it will break the functionality.

Anyone aware what causes this in authChange listners?

答案1

得分: 1

问题基本上是因为您的状态已经被销毁。从您的代码中我们无法知道在小部件树中发生了什么。因此，您的页面随时可能被销毁，您可以通过使用 State 类的 "mounted" 属性来处理这种情况。只要您的小部件不在小部件树中，这个属性就会为 false。因此，您可以在使用 setState 时进行检查，如下所示：

if (mounted) {
    setState(() {});
}

if(mounted) {
    setState((){});
}