Question

我在此 dart 文件中收到此错误“在构建期间调用了 setState() 或 markNeedsBuild()”。在这里，我正在调用 Futurebuilder 来获取用户（）身份验证信息，基本上我是在检查用户是否已登录，然后我将移动到相应的屏幕。

我正在粘贴代码以供参考。谢谢。

import 'package:flutter/material.dart';
import 'package:mukti/ui_pages/login_signup/login_screen.dart';
import 'package:firebase_auth/firebase_auth.dart' as auth;
import 'package:mukti/ui_pages/main_screen/main_screen.dart';
import 'package:provider/provider.dart';

import 'authService.dart';

class CheckAuthentication extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: FutureBuilder(
        future: Provider.of<AuthService>(context, listen: false).getUser(),
        builder: (context, AsyncSnapshot<auth.User> snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            if (snapshot.error != null) {
              print("error");
              return Text(snapshot.error.toString());
            }
            return snapshot.hasData ? MainScreen(firebaseUser: snapshot.data) : LoginScreen();
          } else {
            return LoadingCircle();
          }
        }
      )
    );
  }
}

class LoadingCircle extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        child: CircularProgressIndicator(
          backgroundColor: Theme.of(context).colorScheme.primaryVariant,
        ),
        alignment: Alignment(0.0, 0.0),
      ),
    );
  }
}

供参考的异常信息

════════ Exception caught by foundation library ════════════════════════════════════════════════════
The following assertion was thrown while dispatching notifications for AuthService:
setState() or markNeedsBuild() called during build.

This _InheritedProviderScope<AuthService> widget cannot be marked as needing to build because the framework is already in the process of building widgets.  A widget can be marked as needing to be built during the build phase only if one of its ancestors is currently building. This exception is allowed because the framework builds parent widgets before children, which means a dirty descendant will always be built. Otherwise, the framework might not visit this widget during this build phase.
The widget on which setState() or markNeedsBuild() was called was: _InheritedProviderScope<AuthService>
  value: Instance of 'AuthService'
  listening to value
The widget which was currently being built when the offending call was made was: CheckAuthentication
  dirty
When the exception was thrown, this was the stack: 
#0      Element.markNeedsBuild.<anonymous closure> (package:flutter/src/widgets/framework.dart:4292:11)
#1      Element.markNeedsBuild (package:flutter/src/widgets/framework.dart:4307:6)
#2      _InheritedProviderScopeElement.markNeedsNotifyDependents (package:provider/src/inherited_provider.dart:496:5)
#3      ChangeNotifier.notifyListeners (package:flutter/src/foundation/change_notifier.dart:226:25)
#4      AuthService.getUser (package:mukti/authentication/authService.dart:18:7)
...
The AuthService sending notification was: Instance of 'AuthService'
════════════════════════════════════════════════════════════════════════════════════════════════════

Answer 1

请改用此代码：

import 'package:flutter/material.dart';
import 'package:mukti/ui_pages/login_signup/login_screen.dart';
import 'package:firebase_auth/firebase_auth.dart' as auth;
import 'package:mukti/ui_pages/main_screen/main_screen.dart';
import 'package:provider/provider.dart';

import 'authService.dart';

class CheckAuthentication extends StatelessWidget {


  @override
  Widget build(BuildContext context) {
    final authService = Provider.of<AuthService>(context, listen: false);

    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: FutureBuilder(
        future: authService.getUser(),
        builder: (context, AsyncSnapshot<auth.User> snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            if (snapshot.error != null) {
              print("error");
              return Text(snapshot.error.toString());
            }
            return snapshot.hasData ? MainScreen(firebaseUser: snapshot.data) : LoginScreen();
          } else {
            return LoadingCircle();
          }
        }
      )
    );
  }
}

class LoadingCircle extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        child: CircularProgressIndicator(
          backgroundColor: Theme.of(context).colorScheme.primaryVariant,
        ),
        alignment: Alignment(0.0, 0.0),
      ),
    );
  }
}

Answer 2

您的问题是调用notifyListeners()在getUser()功能。删除该行和错误会自行消失。此尝试构建微件树和FutureBuilder是构建的过程

Answer 3

getUser() 供参考

final auth.FirebaseAuth _auth = auth.FirebaseAuth.instance;

  Future<auth.User> getUser() async {
    try {
      final user = _auth.currentUser;
      if (user != null) {
        print('User signed in: ${user.email}');
      } else {
        print('No user signed in');
      }
      notifyListeners();
      return user;
    } catch (e) {
      print(e);
      return null;
    }
  }

接收错误“在构建过程中调用了 setState() 或 markNeedsBuild()”

供参考的异常信息

3 个答案: