Flutter Firebase Cloud Messaging onMessage is triggered twice

Question

I already implemented the basic configuration suggested by the firebase_messaging flutter package. However, each time that I receive a notification on my flutter app onMessage is triggered twice. I'm using firebase_messaging 6.0.9, Dart 2.7.0 and Flutter 1.12.13+hotfix.5.

This is my [project]/android/build.gradle

    buildscript {
    repositories {
        google()
        jcenter()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.0'
        classpath 'com.google.gms:google-services:4.3.2'
    }
}

allprojects {
    repositories {
        google()
        jcenter()
    }
}

rootProject.buildDir = '../build'
   subprojects {
       project.buildDir = "${rootProject.buildDir}/${project.name}"
   }
   subprojects {
       project.evaluationDependsOn(':app')
   }

   task clean(type: Delete) {
       delete rootProject.buildDir
   }

This is my [project]/android/app/build.gradle

def localProperties = new Properties()
def localPropertiesFile = rootProject.file('local.properties')
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader('UTF-8') { reader ->
        localProperties.load(reader)
    }
}

def flutterRoot = localProperties.getProperty('flutter.sdk')
if (flutterRoot == null) {
    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
}

def flutterVersionCode = localProperties.getProperty('flutter.versionCode')
if (flutterVersionCode == null) {
    flutterVersionCode = '1'
}

def flutterVersionName = localProperties.getProperty('flutter.versionName')
if (flutterVersionName == null) {
    flutterVersionName = '1.0'
}

apply plugin: 'com.android.application'
apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"

android {
    compileSdkVersion 28

    lintOptions {
        disable 'InvalidPackage'
    }

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId "com.example.chat_notification"
        minSdkVersion 16
        targetSdkVersion 28
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            signingConfig signingConfigs.debug
        }
    }
}

flutter {
    source '../..'
}

dependencies {
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test:runner:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.1.1'
}

apply plugin: 'com.google.gms.google-services'

And this is the code where the onMessage is triggered twice

import 'package:chat_notification/model/message.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';

class MessageWidget extends StatefulWidget {
  @override
  _MessageWidgetState createState() => _MessageWidgetState();
}

class _MessageWidgetState extends State<MessageWidget> {

  FirebaseMessaging _firebaseMessaging = FirebaseMessaging();
  List<Message> messages = [];

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> response) async {
        print("onMessage: $response");
      },
      onLaunch: (Map<String, dynamic> response) async {
        print("onLaunch: $response");
      },
      onResume: (Map<String, dynamic> response) async {
        print("onResume: $response");
      },
    );
  }

  @override
  Widget build(BuildContext context) => ListView(
    children: messages.map(buildMessage).toList(),
  );

  Widget buildMessage(Message message) => ListTile(
    title: Text(message.title),
    subtitle: Text(message.body),
  );
}

I already try creating new projects but it seems to happen for each of them. I would really appreciate if anyone can help me about this.

EDIT:

This is no longer present in latest version of firebase_messaging: 7.0.0. Best solution I found is updating the package. Duplicated messages are not longer present.

Answer 1

Update:

This is no longer present in latest version of firebase_messaging (7.0.0 or up). Best solution I found is updating the package. Duplicated messages are not longer present.

Original Solution:

I am facing the same problem. I don't know the reason or the solution for it. A simple way-around is using a even odd counter to catch only one of the two callbacks.

import 'package:chat_notification/model/message.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';

class MessageWidget extends StatefulWidget {
  @override
  _MessageWidgetState createState() => _MessageWidgetState();
}

class _MessageWidgetState extends State<MessageWidget> {

  FirebaseMessaging _firebaseMessaging = FirebaseMessaging();
  List<Message> messages = [];
  static int i = 0;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> response) async {
        if(i%2==0) {
          print("onMessage: $response");
          // something else you wanna execute
        };
        i++;
      },
      onLaunch: (Map<String, dynamic> response) async {
        print("onLaunch: $response");
      },
      onResume: (Map<String, dynamic> response) async {
        print("onResume: $response");
      },
    );
  }

  @override
  Widget build(BuildContext context) => ListView(
    children: messages.map(buildMessage).toList(),
  );

  Widget buildMessage(Message message) => ListTile(
    title: Text(message.title),
    subtitle: Text(message.body),
  );
}

This will run the code only once! Can be used for onLaunch and onResume similarly.

Answer 2

I faced this issue with firebase_messaging: ^10.0.4

Going through literature, I see that this is a bug that keeps occurring every now and then across versions.

Knowing that, I personally wouldn't use the methods mentioned in the answer (using a boolean flag, odd/even flag).

I got around the issue by using a time controlled semaphore.

static int semaphore = 0;

FirebaseMessaging.onMessage.listen((RemoteMessage message) {
  if (semaphore != 0) {
    return;
  }
  semaphore = 1;
  Future.delayed(Duration).then((_) => semaphore = 0);
  handleMessage(message);
});

Also avoids concurrent remote message launches (based on the Duration you pass) - though I can't imagine a real world situation where remote messages might be launched concurrently.