Firebase Messaging - Null check operator used on a null value? - flutter

Question

import 'dart:developer';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:permission_handler/permission_handler.dart';
import '../../export.dart';
class FirebaseNotificationManager {
FirebaseNotificationManager._privateConstructor();
static final FirebaseNotificationManager _instance = FirebaseNotificationManager._privateConstructor();
factory FirebaseNotificationManager() {
return _instance;
}
init() async {
// add firebase notification permission
FirebaseMessaging messaging = FirebaseMessaging.instance;
NotificationSettings settings = await messaging.requestPermission(
alert: true,
announcement: false,
badge: true,
carPlay: false,
criticalAlert: true,
provisional: false,
sound: true,
);
if (await Permission.notification.request().isGranted) {
try {
// Either the permission was already granted before or the user just granted it.
FirebaseMessaging.onBackgroundMessage(_messageHandler);
_firebaseMessagingListener();
String? deviceToken = await FirebaseMessaging.instance.getToken();
logger.i(deviceToken);
} catch (e) {
logger.i(e);
}
}
}
/// must call it from view after getContext is initialized to show dialog message
checkAndroid() async {
if (!(await Permission.notification.request().isGranted) && GetPlatform.isAndroid) {
showOptionsDialog(
text: 'إذا كنت ترغب في تلقي الاشعارات ،برجاء اعطاء إذن الاشعارات في الإعدادات وإعادة تشغيل التطبيق',
yesFunction: (context) async {
openAppSettings();
});
}
}
// execute if app in background
Future<void> _messageHandler(RemoteMessage message) async {
// Data notificationMessage = Data.fromJson(message.data);
log('notification from background : ${message.toMap()}');
}
// execute if app in foreground
void _firebaseMessagingListener() {
FirebaseMessaging.onMessage.listen((RemoteMessage message) {
logger.i('Got a message whilst in the foreground!');
logger.i('Message data: ${message.data}');
if (message.notification != null) {
logger.i('Message also contained a notification: ${message.notification!.toMap()}');
logger.i('Message also contained a notification: ${message.toMap()}');
// that means new message
try {
Get.snackbar(message.notification!.title.toString(), message.notification!.body.toString(),
duration: Duration(seconds: 6),
backgroundColor: Theme.of(Get.context!).cardColor,
barBlur: 10,
margin: EdgeInsets.all(10),
padding: EdgeInsets.all(8));
} catch (e) {
logger.i(e);
}
}
});
}
}

Answer 1

As per the documentation, you need to put the onBackgroundMessage function outside of a class, at the top of your file as a top-level function. See Firebase messaging example for implementation.
source
file became:
import 'dart:developer';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:permission_handler/permission_handler.dart';
import '../../export.dart';
init() async {
// add firebase notification permission
FirebaseMessaging messaging = FirebaseMessaging.instance;
NotificationSettings settings = await messaging.requestPermission(
alert: true,
announcement: false,
badge: true,
carPlay: false,
criticalAlert: true,
provisional: false,
sound: true,
);
if (await Permission.notification.request().isGranted) {
try {
// Either the permission was already granted before or the user just granted it.
FirebaseMessaging.onBackgroundMessage(_messageHandler);
_firebaseMessagingListener();
String? deviceToken = await FirebaseMessaging.instance.getToken();
logger.i(deviceToken);
} catch (e) {
logger.i(e);
}
}
}
/// must call it from view after getContext is initialized to show dialog message
checkAndroid() async {
if (!(await Permission.notification.request().isGranted) && GetPlatform.isAndroid) {
showOptionsDialog(
text: 'إذا كنت ترغب في تلقي الاشعارات ،برجاء اعطاء إذن الاشعارات في الإعدادات وإعادة تشغيل التطبيق',
yesFunction: (context) async {
openAppSettings();
});
}
}
// execute if app in background
Future<void> _messageHandler(RemoteMessage message) async {
// Data notificationMessage = Data.fromJson(message.data);
log('notification from background : ${message.toMap()}');
}
// execute if app in foreground
void _firebaseMessagingListener() {
FirebaseMessaging.onMessage.listen((RemoteMessage message) {
logger.i('Got a message whilst in the foreground!');
logger.i('Message data: ${message.data}');
if (message.notification != null) {
logger.i('Message also contained a notification: ${message.notification!.toMap()}');
logger.i('Message also contained a notification: ${message.toMap()}');
// that means new message
try {
Get.snackbar(message.notification!.title.toString(), message.notification!.body.toString(),
duration: Duration(seconds: 6),
backgroundColor: Theme.of(Get.context!).cardColor,
barBlur: 10,
margin: EdgeInsets.all(10),
padding: EdgeInsets.all(8));
} catch (e) {
logger.i(e);
}
}
});
}