Flutter Riverpod 値の代入のやりかたがわからないです。

Question

前提・実現したいこと

emailProviderに、メールアドレスを保存しておきたいです。
理由は、ほかのWidgetで値を参照してユーザー認証をするために必要だからです。

発生している問題・エラーメッセージ

StateNotifierListenerError (At least listener of the StateNotifier Instance of 'StateController<String>' threw an exception
when the notifier tried to update its state.

The exceptions thrown are:

setState() or markNeedsBuild() called during build.
This UncontrolledProviderScope 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:
  UncontrolledProviderScope
The widget which was currently being built when the offending call was made was:
  StreamBuilder<User?>

該当のソースコード

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:hooks_riverpod/hooks_riverpod.dart';
import 'package:sample/video/video_page.dart';
import 'login/login_page.dart';
import 'menu/programs_wiget.dart';
import 'package:firebase_auth/firebase_auth.dart';

final emailProvider = StateProvider((ref) {
  return '';
});
void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(
    const ProviderScope(child: Root()),
  );
}

class Root extends StatelessWidget {
  const Root({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Pygmalion",
      theme: ThemeData(
        fontFamily: "MPLUS2",
      ),
      home: StreamBuilder<User?>(
        stream: FirebaseAuth.instance.authStateChanges(),
        builder: (context, snapshot) {
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const SizedBox();
          }
          if (snapshot.hasData) {
            context.read(emailProvider).state = "[e-mail]";

            return const ProgramWidget();
          }

          return LoginPage();
        },
      ),
    );
  }
}

試したこと

emailproviderに、"[e-mail]"を代入したいです。

Answer 1

このエラーは StreamBuilderの中で

context.read(emailProvider).state = "[e-mail]";

を実行したことにより、wigetがbuildされているときに、またstateが更新され、buildする羽目になったことにより、発生したエラーです。
なのでbuildが終わった直後にこれを実行しないといけません。

WidgetsBinding.instance.addPostFrameCallback((_) => context.read(emailProvider).state = "[e-mail]");

こうすると良いかもしれません。
詳しくはここです。