Flutter集成Amplify Auth Plugin时“插件未添加”报错排查

报错日志 #

> Launching lib/main.dart on 2109119DG in debug mode...
Running Gradle task 'assembleDebug'...
✓  Built build/app/outputs/flutter-apk/app-debug.apk.
Debug service listening on ws://xxxx
Syncing files to device 2109119DG...
I/amplify:flutter:auth_cognito(27806): Added Auth plugin
E/flutter (27806): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: AmplifyException(message: Auth plugin has not been added to Amplify, recoverySuggestion: Add Auth plugin to Amplify and call configure before calling Auth related APIs, underlyingException: null)
E/flutter (27806): #0      AuthCategory.fetchAuthSession (package:amplify_core/src/category/amplify_auth_category.dart:189:11)
E/flutter (27806): #1      _MyAppState.isUserSignedIn (package:base_app/main.dart:37:39)
E/flutter (27806): #2      _MyAppState.build (package:flutter/src/widgets/framework.dart:4992:27)
E/flutter (27806): #3      StatefulElement.build (package:flutter/src/widgets/framework.dart:4878:15)
E/flutter (27806): #4      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4878:15)
E/flutter (27806): #5      StatefulElement.performRebuild (package:flutter/src/widgets/framework.dart:5050:11)
E/flutter (27806): #6      Element.rebuild (package:flutter/src/widgets/framework.dart:4604:5)
E/flutter (27806): #7      ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:4859:5)
E/flutter (27806): #8      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:5041:11)
E/flutter (27806): #9      ComponentElement.mount (package:flutter/src/widgets/framework.dart:4853:5)
E/flutter (27806): #10     Element.inflateWidget (package:flutter/src/widgets/framework.dart:3863:16)
E/flutter (27806): #11     Element.updateChild (package:flutter/src/widgets/framework.dart:3592:18)
E/flutter (27806): #12     RenderObjectToWidgetElement._rebuild (package:flutter/src/widgets/binding.dart:1195:16)
E/flutter (27806): #13     RenderObjectToWidgetElement.mount (package:flutter/src/widgets/binding.dart:1164:5)
E/flutter (27806): #14     RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure> (package:flutter/src/widgets/binding.dart:1111:18)
E/flutter (27806): #15     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2605:19)
E/flutter (27806): #16     RenderObjectToWidgetAdapter.attachToRenderTree (package:flutter/src/widgets/binding.dart:1110:13)
E/flutter (27806): #17     WidgetsBinding.attachRootWidget (package:flutter/src/widgets/binding.dart:945:7)
E/flutter (27806): #18     WidgetsBinding.scheduleAttachRootWidget.<anonymous closure> (package:flutter/src/widgets/binding.dart:925:7)
E/flutter (27806): #19     Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:18:15)
E/flutter (27806): #20     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
E/flutter (27806): #21     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
E/flutter (27806): #22     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:192:12)
E/flutter (27806): 
D/AWSMobileClient(27806): Using the SignInProviderConfig from `awsconfiguration.json`.
D/AWSMobileClient(27806): Inspecting user state details
I/flutter (27806): Successfully configured
D/AWSMobileClient(27806): Inspecting user state details
I/TetheringManager(27806): registerTetheringEventCallback:com.dontknow.base_app
D/AWSMobileClient(27806): hasFederatedToken: false provider: cognito-idp.eu-central-1.amazonaws.com/eu-central-1_xxxx
D/AWSMobileClient(27806): hasFederatedToken: false provider: cognito-idp.eu-central-1.amazonaws.com/eu-central-1_xxxx
D/AWSMobileClient(27806): Inspecting user state details
D/AWSMobileClient(27806): hasFederatedToken: true provider: cognito-idp.eu-central-1.amazonaws.com/eu-central-1_xxxx
D/AWSMobileClient(27806): waitForSignIn: userState:SIGNED_IN
D/AWSMobileClient(27806): getCredentials: Validated user is signed-in

问题说明 #

严格按照AWS教程实现，在调用Amplify.configure前已添加Auth插件，日志也显示插件已加载，但获取会话时仍提示插件未添加。

相关代码（main.dart） #

State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
    _configureAmplify();
  }

  void _configureAmplify() async {
    try {
      await Amplify.addPlugin(AmplifyAuthCognito());
      await Amplify.configure(amplifyconfig);
      print('Successfully configured');
    } on Exception catch (e) {
      print('Error configuring Amplify: $e');
    }
  }

  Future<bool> isUserSignedIn() async {
    final result = await Amplify.Auth.fetchAuthSession();
    return result.isSignedIn;
  }

  @override
  Widget build(BuildContext context) {
    return Authenticator(
      child: MaterialApp(
        builder: Authenticator.builder(),
        home: FutureBuilder(
            future: isUserSignedIn(),
            builder: (BuildContext ctx, AsyncSnapshot snapshot) {
              if (snapshot.data == null) {
                return const Center(
                  child: CircularProgressIndicator(),
                );
              } else {
                return Text("logged in");
              }
            }),
      ),
    );
  }
}

解决方案 #

问题核心是Amplify初始化完成前，FutureBuilder就调用了isUserSignedIn()。initState中的_configureAmplify是异步方法，不会阻塞UI构建，导致build执行时Amplify还未完成插件添加和配置。

修复步骤 #

1. 在状态类中添加标记变量，记录Amplify是否初始化完成：

bool _amplifyConfigured = false;

2. 修改_configureAmplify方法，初始化完成后更新状态：

void _configureAmplify() async {
  try {
    await Amplify.addPlugin(AmplifyAuthCognito());
    await Amplify.configure(amplifyconfig);
    setState(() {
      _amplifyConfigured = true;
    });
    print('Successfully configured');
  } on Exception catch (e) {
    print('Error configuring Amplify: $e');
  }
}

3. 在build方法中，仅当Amplify初始化完成后才渲染FutureBuilder，否则显示加载状态：

@override
Widget build(BuildContext context) {
  return Authenticator(
    child: MaterialApp(
      builder: Authenticator.builder(),
      home: _amplifyConfigured 
          ? FutureBuilder(
              future: isUserSignedIn(),
              builder: (BuildContext ctx, AsyncSnapshot snapshot) {
                if (snapshot.data == null) {
                  return const Center(child: CircularProgressIndicator());
                } else {
                  return Text("logged in");
                }
              })
          : const Center(child: CircularProgressIndicator()),
    ),
  );
}

额外提示 #

• 也可以将isUserSignedIn的调用放在Amplify初始化完成后，比如在_configureAmplify的setState前执行，将登录状态保存到变量，避免FutureBuilder重复调用。
• 确认amplifyconfig常量正确导入，配置文件内容无误。

内容的提问来源于stack exchange，提问作者Muleque