我正在尝试从一个Node.js API向Flutter应用程序发送通知。首先，我希望我的应用程序能够从Firebase接收通知。
但是，当我调用initializeApp时，出现了问题：
PlatformException (PlatformException(null-error, Host platform returned null value for non-null return value., null, null))
并且，在控制台中显示了这个错误信息：
E/flutter (25357): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: PlatformException(null-error, Host platform returned null value for non-null return value., null, null)
E/flutter (25357): #0 FirebaseCoreHostApi.optionsFromResource (package:firebase_core_platform_interface/src/pigeon/messages.pigeon.dart:250)
package:firebase_core_platform_interface/…/pigeon/messages.pigeon.dart:1
E/flutter (25357): <asynchronous suspension>
E/flutter (25357): #1 MethodChannelFirebase.initializeApp (package:firebase_core_platform_interface/src/method_channel/method_channel_firebase.dart:89)
package:firebase_core_platform_interface/…/method_channel/method_channel_firebase.dart:1
E/flutter (25357): <asynchronous suspension>
E/flutter (25357): #2 Firebase.initializeApp (package:firebase_core/src/firebase.dart:40)
package:firebase_core/src/firebase.dart:1
E/flutter (25357): <asynchronous suspension>
E/flutter (25357): #3 main (package:notifappfcm/main.dart:13)
package:notifappfcm/main.dart:1
我一直在寻找解决这个问题的方法，但我真的找不到。
这是我的应用程序代码：
main.dart
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'mainscreen.dart';
Future<void> _firebadeMessagingBackgroundHandler(RemoteMessage message) async {
await Firebase.initializeApp(); // options: DefaultFirebaseConfig.platformOptions
print('Handling a background message ${message.messageId}');
}
void main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
FirebaseMessaging.onBackgroundMessage(_firebadeMessagingBackgroundHandler);
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MainScreen(),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({Key? key, required this.title}) : super(key: key);
final String title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
void initState() {
super.initState();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: const Icon(Icons.add),
),
);
}
}
mainscreen.dart
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';
class MainScreen extends StatefulWidget {
const MainScreen({Key? key}) : super(key: key);
@override
State<MainScreen> createState() => _MainScreenState();
}
class _MainScreenState extends State<MainScreen> {
late AndroidNotificationChannel channel;
late FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin;
@override
void initState() {
super.initState();
requestPermission();
loadFCM();
listenFCM();
// Get device's notification token
getToken();
}
void getToken() async {
await FirebaseMessaging.instance.getToken().then((token) => print(token));
}
void requestPermission() async {
FirebaseMessaging messaging = FirebaseMessaging.instance;
NotificationSettings settings = await messaging.requestPermission(
alert: true,
announcement: false,
badge: true,
carPlay: false,
criticalAlert: false,
provisional: false,
sound: true,
);
if (settings.authorizationStatus == AuthorizationStatus.authorized) {
print('User granted permission');
} else if (settings.authorizationStatus ==
AuthorizationStatus.provisional) {
print('User granted provisional permission');
} else {
print('User declined or has not accepted permission');
}
}
void listenFCM() async {
FirebaseMessaging.onMessage.listen((RemoteMessage message) {
RemoteNotification? notification = message.notification;
AndroidNotification? android = message.notification?.android;
if (notification != null && android != null && !kIsWeb) {
flutterLocalNotificationsPlugin.show(
notification.hashCode,
notification.title,
notification.body,
NotificationDetails(
android: AndroidNotificationDetails(channel.id, channel.name,
// ignore: todo
// TODO add a proper drawable resource to android (now using one that already exists)
icon: 'launch_background')));
}
});
}
void loadFCM() async {
if (!kIsWeb) {
channel = const AndroidNotificationChannel(
'high_importance_channel', // id
'High Importance Notifications', // title
importance: Importance.high,
enableVibration: true,
);
flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
/// Create an Android Notification Channel.
///
/// We use this channel in the `AndroidManifest.xml` file to override the
/// default FCM channel to enable heads up notifications.
await flutterLocalNotificationsPlugin
.resolvePlatformSpecificImplementation<
AndroidFlutterLocalNotificationsPlugin>()
?.createNotificationChannel(channel);
/// Update the iOS foreground notification presentation options to allow
/// heads up notifications.
await FirebaseMessaging.instance
.setForegroundNotificationPresentationOptions(
alert: true,
badge: true,
sound: true,
);
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Container(
height: 40,
width: 200,
color: Colors.red,
),
));
}
}