GlobalKey<NavigatorState>().currentState.context 在推送时返回 null

如何解决GlobalKey<NavigatorState>().currentState.context 在推送时返回 null

我正在使用 Flutter 本地通知来管理本地通知。我希望当通知类型为“某些用户加入比赛”时，当通知用户点击通知时，他应该被带到比赛详细信息页面。最好的方法是使用 GlobalKey 作为 navigatorKey 并将其传递给 MaterialApp。但是我收到了这个错误。

（P.S.：此应用在 MainFrameApp() 中包含嵌套导航器，因此，在那里处理到 ContestDetailsPage 的进一步导航。）

我找不到原因，上下文为空。我认为使用 ChangeNotifier 的 setState 也可能导致了这个问题。所以我也提供了那个代码。

════════ Exception caught by widgets library ═══════════════════════════════════
The method 'push' was called on null.
Receiver: null
Tried calling: push<dynamic>(Instance of 'MaterialPageRoute<dynamic>')
The relevant error-causing widget was
MaterialApp
lib\main.dart:90

main.dart

import 'dart:convert';

import 'package:firebase_dynamic_links/firebase_dynamic_links.dart';
import 'package:flutter/material.dart';
import 'package:hive/hive.dart';
import 'package:hive_flutter/hive_flutter.dart';
import 'package:path_provider/path_provider.dart' as pathProvider;
import 'package:provider/provider.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:sports_private_pool/models/authentication.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart'
    as local_notification;

import 'models/person.dart';
import 'screens/main_frame_app.dart';
import 'screens/welcome_screen.dart';

bool userLoggedIn = false;
SharedPreferences preferences;

local_notification.FlutterLocalNotificationsPlugin
    flutterLocalNotificationsPlugin =
    local_notification.FlutterLocalNotificationsPlugin();

final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  preferences = await SharedPreferences.getInstance();

  final appDocumentDirectory =
      await pathProvider.getApplicationDocumentsDirectory();
  await Hive.initFlutter(appDocumentDirectory.path);
  Hive.registerAdapter(PersonAdapter());

  await Hive.openBox<dynamic>('userData');
  await Hive.openBox<Person>('user');

  // Flutter Local Notification
  var initializationSettingsAndroid =
      local_notification.AndroidInitializationSettings('@mipmap/ic_launcher');
  var initializationSettingsIOS = local_notification.IOSInitializationSettings(
    requestAlertPermission: true,requestBadgePermission: true,requestSoundPermission: true,onDidReceiveLocalNotification:
        (int id,String title,String body,String payload) async {},);
  var initializationSettings = local_notification.InitializationSettings(
    android: initializationSettingsAndroid,iOS: initializationSettingsIOS,);

  flutterLocalNotificationsPlugin.initialize(
    initializationSettings,onSelectNotification: (String payload) async {
      if (payload != null) {
        try {
          Map<String,dynamic> payloadJson = json.decode(payload);
          if (payloadJson['data']['type'] == 'joinContest') {

            Navigator.push(
              navigatorKey.currentState.context,MaterialPageRoute(
                builder: (context) => MainFrameApp(
                  defaultPage: 2,contestId: payloadJson['data']['contestId'],matchId: payloadJson['data']['matchId'],),);
          }
        } catch (e) {
          print(e);
        }
      } else {
        print("notification payload: $payload");
      }
    },);

  runApp(
    ChangeNotifierProvider(
      create: (context) => Authentication(),child: MaterialApp(
        title: 'Envision',navigatorKey: navigatorKey,theme: ThemeData(accentColor: Colors.black87),debugShowCheckedModeBanner: false,home: Envision(),);
}

class Envision extends StatefulWidget {
  @override
  _EnvisionState createState() => _EnvisionState();
}

class _EnvisionState extends State<Envision> {
  Box<Person> userBox;

  @override
  initState() {
    userBox = Hive.box('user');
    userLoggedIn = preferences.getString('email') != null;
    print("EMAIL: ${preferences.getString('email')}");

    Future.delayed(Duration.zero,() async {
      if (userLoggedIn) {
        Provider.of<Authentication>(context,listen: false)
            .login(userBox.get('user'));
      }
    });

    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Consumer<Authentication>(
      builder: (context,state,child) {
        if (state.loggedIn) {
          return MainFrameApp();
        }
        return WelcomeScreen();
      },);
  }
}

身份验证.dart

import 'package:flutter/foundation.dart';
import 'package:sports_private_pool/core/errors/exceptions.dart';
import 'package:sports_private_pool/models/person.dart';

class Authentication extends ChangeNotifier {
  bool _loggedIn = false;
  Person _user;

  bool get loggedIn => _loggedIn;

  Person get user => _loggedIn ? _user : throw NotFoundException();

  void login(Person user) {
    _loggedIn = true;
    _user = user;
    print("user logged in....");
    notifyListeners();
  }

  void logout() {
    _loggedIn = false;
    print("user logged out...");
    notifyListeners();
  }
}