Flutter local notification initialization errors in background calls

[Somesh-Pant]

I am trying to create an app that fires a simple notification through a background service dispatched by workmanager plugin. The idea is to check for any messages in mqtt instance after every 15 minutes and display a simple local notification in case of the availability of any message on the broker. The notification is called at the initialization of the application too... The main issue is that no matter how many times I terminate the app and restart it the notification works FINE but as soon as I try to dispatch a background service , the service works but the local notification plugin FAILS to initialize.. The code and the logs for the following are as follows.

CODE-
import 'dart:async';

import 'package:workmanager/workmanager.dart';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';

import './mqttClientWrapper.dart';

const mqtt_task_key = "MqttTask";

Future callbackDispatcher() async{
Workmanager.executeTask((taskName, inputData) async{
if(taskName == mqtt_task_key){
print("running instance in background");
print("instantiating");
await RandomState().setup();
}
return Future.value(true);
});
}

class Random extends StatefulWidget {
@OverRide
RandomState createState() => RandomState();
}

class RandomState extends State {
MQTTClientWrapper mqttClientWrapper;

String message = "";

Future setup() async {
FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
mqttClientWrapper = MQTTClientWrapper(() => {},(newMessage) => gotNewMessage(newMessage, flutterLocalNotificationsPlugin));
print('1');
mqttClientWrapper.prepareMqttClient();
print('2');

var initializationSettingsAndroid =
new AndroidInitializationSettings('@mipmap/ic_launcher');
print('3');
var initializationSettingsIOS = new IOSInitializationSettings();
var initializationSettings = new InitializationSettings(
    initializationSettingsAndroid, initializationSettingsIOS);
//flutterLocalNotificationsPlugin = new FlutterLocalNotificationsPlugin();
await flutterLocalNotificationsPlugin.initialize(initializationSettings,
    onSelectNotification: onSelectNotification);

}

Future gotNewMessage(String newMessage, flutterLocalNotificationsPlugin) async{
setState((){
this.message = newMessage;
});
await _showNotificationWithDefaultSound(flutterLocalNotificationsPlugin);
print('test');
}

@OverRide
void initState() {
super.initState();
setup();
Workmanager.cancelAll();
}

@OverRide
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('random'),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
message,
style: Theme.of(context).textTheme.headline4,
),
FlatButton(
color: Colors.blue,
onPressed: (){
Workmanager.initialize(
callbackDispatcher,
isInDebugMode: true,
);
print("initialized");
Workmanager.registerPeriodicTask('1', mqtt_task_key, frequency: Duration(minutes: 15), initialDelay: Duration(seconds: 30));
},
)
],
),
),
);
}

Future onSelectNotification(String payload) async {
showDialog(
context: context,
builder: (_) {
return new AlertDialog(
title: Text("PayLoad"),
content: Text("Payload : $payload"),
);
},
);
}

Future _showNotificationWithDefaultSound(flutterLocalNotificationsPlugin) async {
var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
'your channel id', 'your channel name', 'your channel description',
importance: Importance.Max, priority: Priority.High);
var iOSPlatformChannelSpecifics = new IOSNotificationDetails();
var platformChannelSpecifics = new NotificationDetails(
androidPlatformChannelSpecifics, iOSPlatformChannelSpecifics);
await flutterLocalNotificationsPlugin.show(
0,
'New Post',
'New Message',
platformChannelSpecifics,
payload: 'Default_Sound',
);
}
}

Logs from the console

I/flutter (16424): 1
I/flutter (16424): MQTTClientWrapper::test client connecting....
I/flutter (16424): 2020-08-19 04:01:10.452967 -- Authenticating with username '{wbynzcri}' and password '{uOIqIxMgf3Dl}'
I/flutter (16424): 2020-08-19 04:01:10.489029 -- SynchronousMqttServerConnectionHandler::internalConnect entered
I/flutter (16424): 2020-08-19 04:01:10.489300 -- SynchronousMqttServerConnectionHandler::internalConnect - initiating connection try 0
I/flutter (16424): 2020-08-19 04:01:10.489672 -- SynchronousMqttServerConnectionHandler::internalConnect - insecure TCP selected
I/flutter (16424): 2
I/flutter (16424): 3
I/flutter (16424): 2020-08-19 04:01:11.724721 -- MqttServerConnection::_startListening
I/flutter (16424): 2020-08-19 04:01:11.742755 -- SynchronousMqttServerConnectionHandler::internalConnect - connection complete
I/flutter (16424): 2020-08-19 04:01:11.743072 -- SynchronousMqttServerConnectionHandler::internalConnect sending connect message
I/flutter (16424): 2020-08-19 04:01:11.748088 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.connect
I/flutter (16424): Header: MessageType = MqttMessageType.connect, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): Connect Variable Header: ProtocolName=MQIsdp, ProtocolVersion=3, ConnectFlags=Connect Flags: Reserved1=false, CleanStart=true, WillFlag=false, WillQos=MqttQos.atMostOnce, WillRetain=false, PasswordFlag=true, UserNameFlag=true, KeepAlive=60
I/flutter (16424): MqttConnectPayload - client identifier is : #
I/flutter (16424): 2020-08-19 04:01:11.780464 -- SynchronousMqttServerConnectionHandler::internalConnect - pre sleep, state = Connection status is connecting with return code of noneSpecified and a disconnection origin of none
I/flutter (16424): 2020-08-19 04:01:12.118299 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:12.137902 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.connectAck
I/flutter (16424): Header: MessageType = MqttMessageType.connectAck, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 2
I/flutter (16424): Connect Variable Header: TopicNameCompressionResponse={0}, ReturnCode={MqttConnectReturnCode.connectionAccepted}
I/flutter (16424): 2020-08-19 04:01:12.144405 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.153670 -- SynchronousMqttServerConnectionHandler::_connectAckProcessor
I/flutter (16424): 2020-08-19 04:01:12.154185 -- SynchronousMqttServerConnectionHandler::_connectAckProcessor - state = connected
I/flutter (16424): MQTTClientWrapper::OnConnected client callback - Client connection was sucessful
I/flutter (16424): 2020-08-19 04:01:12.156048 -- SynchronousMqttServerConnectionHandler:: cancelling connect timer
I/flutter (16424): 2020-08-19 04:01:12.158088 -- SynchronousMqttServerConnectionHandler::internalConnect - post sleep, state = Connection status is connected with return code of connectionAccepted and a disconnection origin of none
I/flutter (16424): 2020-08-19 04:01:12.158600 -- SynchronousMqttServerConnectionHandler::internalConnect exited with state Connection status is connected with return code of connectionAccepted and a disconnection origin of none
I/flutter (16424): MQTTClientWrapper::Mosquitto client connected
I/flutter (16424): MQTTClientWrapper::Subscribing to the 4060431/# topic
I/flutter (16424): 2020-08-19 04:01:12.177163 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.subscribe
I/flutter (16424): Header: MessageType = MqttMessageType.subscribe, Duplicate = false, Retain = false, Qos = MqttQos.atLeastOnce, Size = 0
I/flutter (16424): Subscribe Variable Header: MessageIdentifier={1}
I/flutter (16424): Payload: Subscription [{1}]
I/flutter (16424): {{ Topic={4060431/#}, Qos={MqttQos.atMostOnce} }}
I/flutter (16424):
I/flutter (16424): 2020-08-19 04:01:12.492990 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:12.500615 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.subscribeAck
I/flutter (16424): Header: MessageType = MqttMessageType.subscribeAck, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 3
I/flutter (16424): SubscribeAck Variable Header: MessageIdentifier={1}
I/flutter (16424): Payload: Qos grants [{1}]
I/flutter (16424): {{ Grant={MqttQos.atMostOnce} }}
I/flutter (16424):
I/flutter (16424): 2020-08-19 04:01:12.501061 -- MqttServerConnection::_onData - message processed
I/flutter (16424): MQTTClientWrapper::Subscription confirmed for topic 4060431/#
I/flutter (16424): 2020-08-19 04:01:12.897098 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:12.920910 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 19
I/flutter (16424): Publish Variable Header: TopicName={4060431/offline/}, MessageIdentifier={0}, VH Length={18}
I/flutter (16424): Payload: {1 bytes={<49>
I/flutter (16424): 2020-08-19 04:01:12.921398 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.923384 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 45
I/flutter (16424): Publish Variable Header: TopicName={4060431/information/codename/}, MessageIdentifier={0}, VH Length={31}
I/flutter (16424): Payload: {14 bytes={<83><77><82><84><65><76><82><84><49><66><50><76><49><71>
I/flutter (16424): 2020-08-19 04:01:12.924024 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.926510 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 33
I/flutter (16424): Publish Variable Header: TopicName={4060431/information/version/}, MessageIdentifier={0}, VH Length={30}
I/flutter (16424): Payload: {3 bytes={<48><46><49>
I/flutter (16424): 2020-08-19 04:01:12.926893 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.928255 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 27
I/flutter (16424): Publish Variable Header: TopicName={4060431/sensor/0/type/}, MessageIdentifier={0}, VH Length={24}
I/flutter (16424): Payload: {3 bytes={<71><65><83>
I/flutter (16424): 2020-08-19 04:01:12.928666 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:12.929900 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.publish
I/flutter (16424): Header: MessageType = MqttMessageType.publish, Duplicate = false, Retain = true, Qos = MqttQos.atMostOnce, Size = 26
I/flutter (16424): Publish Variable Header: TopicName={4060431/sensor/0/state/}, MessageIdentifier={0}, VH Length={25}
I/flutter (16424): Payload: {1 bytes={<49>
I/flutter (16424): 2020-08-19 04:01:12.930394 -- MqttServerConnection::_onData - message processed
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE 1
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE SMRTALRT1B2L1G
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE 0.1
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE GAS
I/flutter (16424): MQTTClientWrapper::GOT A NEW MESSAGE 1
I/flutter (16424): test
I/flutter (16424): test
I/flutter (16424): test
I/flutter (16424): test
I/flutter (16424): test
I/art (16424): Do partial code cache collection, code=21KB, data=30KB
I/art (16424): After code cache collection, code=21KB, data=30KB
I/art (16424): Increasing code cache capacity to 128KB
I/flutter (16424): initialized
I/flutter (16424): 2020-08-19 04:01:30.486502 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.pingRequest
I/flutter (16424): Header: MessageType = MqttMessageType.pingRequest, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:30.807658 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:30.811320 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.pingResponse
I/flutter (16424): Header: MessageType = MqttMessageType.pingResponse, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:30.812317 -- MqttServerConnection::_onData - message processed
I/flutter (16424): 2020-08-19 04:01:50.502517 -- MqttConnectionHandlerBase::sendMessage - MQTTMessage of type MqttMessageType.pingRequest
I/flutter (16424): Header: MessageType = MqttMessageType.pingRequest, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:50.833619 -- MqttConnection::_onData
I/flutter (16424): 2020-08-19 04:01:50.834847 -- MqttServerConnection::_onData - message received MQTTMessage of type MqttMessageType.pingResponse
I/flutter (16424): Header: MessageType = MqttMessageType.pingResponse, Duplicate = false, Retain = false, Qos = MqttQos.atMostOnce, Size = 0
I/flutter (16424): 2020-08-19 04:01:50.835866 -- MqttServerConnection::_onData - message processed
I/flutter (16424): running instance in background
I/flutter (16424): instantiating
I/flutter (16424): 1
I/flutter (16424): MQTTClientWrapper::test client connecting....
I/flutter (16424): 2020-08-19 04:01:53.864177 -- Authenticating with username '{wbynzcri}' and password '{uOIqIxMgf3Dl}'
I/flutter (16424): 2020-08-19 04:01:53.918924 -- SynchronousMqttServerConnectionHandler::internalConnect entered
I/flutter (16424): 2020-08-19 04:01:53.919223 -- SynchronousMqttServerConnectionHandler::internalConnect - initiating connection try 0
I/flutter (16424): 2020-08-19 04:01:53.919650 -- SynchronousMqttServerConnectionHandler::internalConnect - insecure TCP selected
I/flutter (16424): 2
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): Failed to handle method call
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Intent android.app.Activity.getIntent()' on a null object reference
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin.initialize(FlutterLocalNotificationsPlugin.java:856)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin.onMethodCall(FlutterLocalNotificationsPlugin.java:742)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:226)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:85)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:631)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.os.MessageQueue.nativePollOnce(Native Method)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.os.MessageQueue.next(MessageQueue.java:323)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.os.Looper.loop(Looper.java:136)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at android.app.ActivityThread.main(ActivityThread.java:6165)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
E/MethodChannel#dexterous.com/flutter/local_notifications(16424): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)
I/WM-WorkerWrapper(16424): Worker result FAILURE for Work [ id=9519d0f6-1acd-445d-a325-8281ae5dd445, tags={ be.tramckrijte.workmanager.BackgroundWorker } ]

Note that the initialized is printed on the console once the background task is fired ... and there is a delay of 30 seconds between the actual execution of the task and the command that is why you will see mqtt instance messages in between ...
The main issue starts form method call.
Please urgent help is required on the matter
Thank You

[MaikuB]

I pushed a branch up that should fix the initialize calls. If you could reference the guard_intent branch in your app to confirm then that would be great. May not solve your problem of getting both plugins working together as it's not something I can help with but should at least fix the crash. For info on how to reference packages via git, please refer to https://dart.dev/tools/pub/dependencies#git-packages. You'll need to make sure to include the path entry (set to flutter_local_notifications) as the plugin isn't located at the root of the repo

[g123k]

I can confirm that your guard_intent branch fixes the Attempt to invoke virtual method 'android.content.Intent android.app.Activity.getIntent()' on a null object reference error

[MaikuB]

Thanks, I'll will merge this in and release it shortly

[Somesh-Pant]

Thank you for the swift response ... I will check the solution and will let you know the response of the app

[saravananmnm]

When i receive the notification from background, getting error on console.

Flutter 1.20.2 • channel stable • https://github.com/flutter/flutter.git
Framework • revision bbfbf1770c (8 days ago) • 2020-08-13 08:33:09 -0700
Engine • revision 9d5b21729f
Tools • Dart 2.9.1

E/MethodChannel#dexterous.com/flutter/local_notifications: Failed to handle method call
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Intent android.app.Activity.getIntent()' on a null object reference
at com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin.initialize(FlutterLocalNotificationsPlugin.java:856)
at com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin.onMethodCall(FlutterLocalNotificationsPlugin.java:742)
at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:230)
at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:85)
at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:692)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:326)
at android.os.Looper.loop(Looper.java:160)
at android.app.ActivityThread.main(ActivityThread.java:6680)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
2020-08-21 19:04:05.212 14786-14821/com.courier_alliance.driver.dev I/flutter: AUCTION LOST ORD2682 641009 to 638011
2020-08-21 19:04:05.212 14786-14821/com.courier_alliance.driver.dev I/flutter: Notification Type ---> 3
2020-08-21 19:04:05.212 14786-14821/com.courier_alliance.driver.dev I/flutter: **************************************
2020-08-21 19:04:05.212 14786-14821/com.courier_alliance.driver.dev I/flutter: FireBase Notification Came
2020-08-21 19:04:05.212 14786-14821/com.courier_alliance.driver.dev I/flutter: **************************************
2020-08-21 19:04:05.240 14786-14821/com.courier_alliance.driver.dev E/flutter: [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: PlatformException(error, Attempt to invoke virtual method 'android.content.Intent android.app.Activity.getIntent()' on a null object reference, null)
#0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:572:7)
#1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:161:18)

#2 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:334:12)
#3 AndroidFlutterLocalNotificationsPlugin.initialize (package:flutter_local_notifications/src/platform_flutter_local_notifications.dart:67:27)
#4 FlutterLocalNotificationsPlugin.initialize (package:flutter_local_notifications/src/flutter_local_notifications_plugin.dart:97:13)
#5 myBackgroundMessageHandler (package:iex_driver/src/helper/customappbar/customappbar.dart:228:35)
#6 _fcmSetupBackgroundChannel. (package:firebase_messaging/firebase_messaging.dart:38:30)
#7 _fcmSetupBackgroundChannel. (package:firebase_messaging/firebase_messaging.dart:31:42)
#8 MethodChannel._handleAsMethodCall (package:flutter/src/services/platform_channel.dart:432:55)
#9 MethodChannel.setMethodCallHandler. (package:flutter/src/services/platform_channel.dart:385:33)
#10 _DefaultBinaryMessenger.handlePlatformMessage (package:flutter/src/services/binding.dart:267:33)
#11 _invoke3. (dart:ui/hooks.dart:282:15)
#12 _rootRun (dart:async/zone.dart:1190:13)
#13 _CustomZone.run (dart:async/zone.dart:1093:19)
#14 _CustomZone.runGuarded (dart:async/zone.dart:997:7)

[MaikuB]

@saravananmnm make sure you're on the latest version

[saravananmnm]

@MaikuB Yes, i have a latest one.
flutter_local_notifications: ^1.4.4+4

[√] Flutter (Channel stable, 1.20.2, on Microsoft Windows [Version 10.0.18362.1016], locale en-IN)
• Flutter version 1.20.2 at C:\Saravanan\Flutter_Sdk\flutter
• Framework revision bbfbf1770c (3 weeks ago), 2020-08-13 08:33:09 -0700
• Engine revision 9d5b21729f
• Dart version 2.9.1

[MaikuB]

@saravananmnm I'd suggest running flutter clean first, get the packages again (e.g. via flutter pub get) and then rebuild the app in case your app still references an old version for whatever reason.

If you're still running into a problem then you'll need to provide complete, minimal example app to reproduce the problem. This could be either a link to a repository or fork the repo and update the example app to demonstrate the problem.