flutter: on background message handler is not being called

Question

I have implemented firebase cloud messaging and firebase functions to my app and used flutter local notifications and added a showNotifications function to make a channel ID and change its importance and priority so i get notifications as heads up (banner), but for some reason the onbackgroundmessagehandler callback is not being called when i send a message from firestore,

here's my code:

  Future<dynamic> myBackgroundMessageHandler(Map<String, dynamic> message) async {
      print('background message handler');
      return await _TabsScreenState()._showNotification(message);
    }

    class TabsScreen extends StatefulWidget {
      static const String id = '/tabs screen';


      @override
      _TabsScreenState createState() => _TabsScreenState();
    }

    class _TabsScreenState extends State<TabsScreen> {
      FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
          FlutterLocalNotificationsPlugin();
      FirebaseMessaging _fcm = FirebaseMessaging();
      Firestore _fireStore = Firestore.instance;

      void _onSaved() async {
        String myToken = await _fcm.getToken();

        if (myToken != null) {
          var tokenRef = _fireStore.collection('tokens').document(myToken);
          print(myToken);

          await tokenRef.setData({
            'token': myToken,
            'createdAt': DateTime.now(),
            'platform': Platform.operatingSystem,
          });
        }
      }

      Future _showNotification(Map<String, dynamic> message) async {
        print('show notifications');
        var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
          'channel id',
          'channel name',
          'channel desc',
          importance: Importance.Max,
          priority: Priority.High,
        );

        var platformChannelSpecifics =
            new NotificationDetails(androidPlatformChannelSpecifics, null);
        await flutterLocalNotificationsPlugin.show(
          0,
          message['notifications']['title'],
          'hi',
          platformChannelSpecifics,
          payload: 'default sound',
        );
      }

      Future selectNotification(String payload) async {
        await flutterLocalNotificationsPlugin.cancelAll();
      }


      void initState() {
        var initializationSettingsAndroid =
            AndroidInitializationSettings('@mipmap/ic_launcher');
        var initializationSettings =
            InitializationSettings(initializationSettingsAndroid, null);
        flutterLocalNotificationsPlugin.initialize(initializationSettings,
            onSelectNotification: selectNotification);
        _onSaved();
        _fcm.configure(
            onBackgroundMessage: myBackgroundMessageHandler,
            onMessage: (Map<String, dynamic> message) async {
              print("On Message: $message");
              print(message['data']['message']);
              showDialog(
                context: context,
                builder: (ctx) {
                  return AlertDialog(
                    content: ListTile(
                      title: Text(message['data']['message']),
                    ),
                    actions: <Widget>[
                      FlatButton(
                        onPressed: () {
                          Navigator.of(context).pop();
                        },
                        child: Text('Ok'),
                      )
                    ],
                  );
                },
              );
            },
            onResume: (Map<String, dynamic> resume) async {
              print("on resume: $resume");
            },
            onLaunch: (Map<String, dynamic> launch) async {
              print("on launch: $launch");
            });



      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
          title: Text("My App"),
        );
      }
    }

here is my andoird manifest:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.tamataapp">
    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
         calls FlutterMain.startInitialization(this); in its onCreate method.
         In most cases you can leave this as-is, but you if you want to provide
         additional functionality it is fine to subclass or reimplement
         FlutterApplication and put your custom class here. "io.flutter.app.FlutterApplication" -->
    <application
        android:name=".Application"
        android:label="tamataapp"
        android:icon="@mipmap/ic_launcher">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">
            <meta-data
                android:name="com.google.firebase.messaging.default_notification_channel_id"
                android:value="default_notification_channel_id”>Channel ID"/>
            <!-- Specifies an Android theme to apply to this Activity as soon as
                 the Android process has started. This theme is visible to the user
                 while the Flutter UI initializes. After that, this theme continues
                 to determine the Window background behind the Flutter UI. -->
            <meta-data
                android:name="io.flutter.embedding.android.NormalTheme"
                android:resource="@style/NormalTheme"
                />
            <!-- Displays an Android View that continues showing the launch screen
                 Drawable until Flutter paints its first frame, then this splash
                 screen fades out. A splash screen is useful to avoid any visual
                 gap between the end of Android's launch screen and the painting of
                 Flutter's first frame. -->
            <meta-data
                android:name="io.flutter.embedding.android.SplashScreenDrawable"
                android:resource="@drawable/launch_background"
                />
            <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
            <action android:name="com.google.firebase.MESSAGING_EVENT" />
            <action android:name="FLUTTER_NOTIFICATION_CLICK" />
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
        </activity>
        <!-- Don't delete the meta-data below.
             This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
        <meta-data
            android:name="flutterEmbedding"
            android:value="2" />
        <service
            android:name=".java.MyFirebaseMessagingService"
            android:exported="false">
        </service>
    </application>
</manifest>

and heres my index.js code:

const functions = require('firebase-functions');
const admin = require('firebase-admin');

admin.initializeApp(functions.config().firebase);

var newData;

exports.messageTrigger = functions.firestore.document('messages/{messagesId}').onCreate(async (snapshot, context) => {


    if (snapshot.empty) {
        console.log('No Devices');
        return;
    }

    newData = snapshot.data();

    const deviceIdTokens = await admin
        .firestore()
        .collection('tokens')
        .get();

    var tokenm = [];

    for (var one of deviceIdTokens.docs) {
        tokenm.push(one.data().token);
    }
    const payload = {
        data: {
          click_action: 'FLUTTER_NOTIFICATION_CLICK',
          message: newData.message,

        }
      };



    try {
        const response = await admin.messaging().sendToDevice(tokenm, payload);
        console.log('Notification sent successfully');
    } catch (err) {
        console.log(err);
    }
});

Answer 1

Based on my experience, onBackgroundMessage not called because one "or all" of these points:

1- onBackgroundMessage does not work if you send a notification in JSON, so delete notification from your JSON to make onBackgroundMessage work.

If notifications set in your JSON, you will see default notification in mobile as a heads up (banner), and onBackgroundMessage will not run.

Update from 2022: on last version of FCM, this problem solved, so you can keep notifications in your JSON...

2- In many cases onBackgroundMessage not called in debugging mode, try test it on release, first run flutter clean then run flutter run --release

3- In many cases you need to set notification priority to high in JSON when send it from server.

Answer 2

What version of firebase_messaging are you using ?

From pub page https://pub.dev/packages/flutter_local_notifications:

Compatibility with firebase_messaging

Previously, there were issues that prevented this plugin working properly with the firebase_messaging plugin. This meant that callbacks from each plugin might not be invoked. Version 6.0.13 of firebase_messaging should resolve this issue so please bump your firebase_messaging dependency and follow the steps covered in firebase_messaging's readme file.