[firebase_messaging] FcmDartService#start doesn't exist on iOS

[Abion47]

I've been chasing an issue around regarding an error message similar to this one that's been happening on my iOS device after calling firebaseMessaging.configure:

MissingPluginException(No implementation found for method FcmDartService#start on channel 
plugins.flutter.io/firebase_messaging)

#0   MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:157:7)
#1   <asynchronous suspension>
#2   MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:332:12)
#3   FirebaseMessaging.configure (package:firebase_messaging/firebase_messaging.dart:126:16)

I followed some of the recommendations listed on that page and nothing worked, so I did some digging into the plugin. As it turns out, the FcmDartService#start method does not exist at all in the iOS native code for the package, and I have confirmed that I don't get the error message on my Android device. Is this an error or should the documentation be updated to note the OS discrepancy?

I am using firebase_messaging: 7.0.2, iOS 13.7, and Android 10.

EDIT: I'd like to clarify that the above error is not preventing notifications from working. Notifications have been working fine on both devices. It's just this error message that pops up on iOS.

[TahaTesser]

Hi @Abion47
Can you please try official example

code sample

// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';

Future<dynamic> myBackgroundMessageHandler(Map<String, dynamic> message) {
  if (message.containsKey('data')) {
    // Handle data message
    final dynamic data = message['data'];
  }

  if (message.containsKey('notification')) {
    // Handle notification message
    final dynamic notification = message['notification'];
  }

  // Or do other work.
}

final Map<String, Item> _items = <String, Item>{};
Item _itemForMessage(Map<String, dynamic> message) {
  final dynamic data = message['data'] ?? message;
  final String itemId = data['id'];
  final Item item = _items.putIfAbsent(itemId, () => Item(itemId: itemId))
    ..status = data['status'];
  return item;
}

class Item {
  Item({this.itemId});
  final String itemId;

  StreamController<Item> _controller = StreamController<Item>.broadcast();
  Stream<Item> get onChanged => _controller.stream;

  String _status;
  String get status => _status;
  set status(String value) {
    _status = value;
    _controller.add(this);
  }

  static final Map<String, Route<void>> routes = <String, Route<void>>{};
  Route<void> get route {
    final String routeName = '/detail/$itemId';
    return routes.putIfAbsent(
      routeName,
      () => MaterialPageRoute<void>(
        settings: RouteSettings(name: routeName),
        builder: (BuildContext context) => DetailPage(itemId),
      ),
    );
  }
}

class DetailPage extends StatefulWidget {
  DetailPage(this.itemId);
  final String itemId;
  @override
  _DetailPageState createState() => _DetailPageState();
}

class _DetailPageState extends State<DetailPage> {
  Item _item;
  StreamSubscription<Item> _subscription;

  @override
  void initState() {
    super.initState();
    _item = _items[widget.itemId];
    _subscription = _item.onChanged.listen((Item item) {
      if (!mounted) {
        _subscription.cancel();
      } else {
        setState(() {
          _item = item;
        });
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Item ${_item.itemId}"),
      ),
      body: Material(
        child: Center(child: Text("Item status: ${_item.status}")),
      ),
    );
  }
}

class PushMessagingExample extends StatefulWidget {
  @override
  _PushMessagingExampleState createState() => _PushMessagingExampleState();
}

class _PushMessagingExampleState extends State<PushMessagingExample> {
  String _homeScreenText = "Waiting for token...";
  bool _topicButtonsDisabled = false;

  final FirebaseMessaging _firebaseMessaging = FirebaseMessaging();
  final TextEditingController _topicController =
      TextEditingController(text: 'topic');

  Widget _buildDialog(BuildContext context, Item item) {
    return AlertDialog(
      content: Text("Item ${item.itemId} has been updated"),
      actions: <Widget>[
        FlatButton(
          child: const Text('CLOSE'),
          onPressed: () {
            Navigator.pop(context, false);
          },
        ),
        FlatButton(
          child: const Text('SHOW'),
          onPressed: () {
            Navigator.pop(context, true);
          },
        ),
      ],
    );
  }

  void _showItemDialog(Map<String, dynamic> message) {
    showDialog<bool>(
      context: context,
      builder: (_) => _buildDialog(context, _itemForMessage(message)),
    ).then((bool shouldNavigate) {
      if (shouldNavigate == true) {
        _navigateToItemDetail(message);
      }
    });
  }

  void _navigateToItemDetail(Map<String, dynamic> message) {
    final Item item = _itemForMessage(message);
    // Clear away dialogs
    Navigator.popUntil(context, (Route<dynamic> route) => route is PageRoute);
    if (!item.route.isCurrent) {
      Navigator.push(context, item.route);
    }
  }

  @override
  void initState() {
    super.initState();
    _firebaseMessaging.configure(
      onMessage: (Map<String, dynamic> message) async {
        print("onMessage: $message");
        _showItemDialog(message);
      },
      onBackgroundMessage: myBackgroundMessageHandler,
      onLaunch: (Map<String, dynamic> message) async {
        print("onLaunch: $message");
        _navigateToItemDetail(message);
      },
      onResume: (Map<String, dynamic> message) async {
        print("onResume: $message");
        _navigateToItemDetail(message);
      },
    );
    _firebaseMessaging.requestNotificationPermissions(
        const IosNotificationSettings(
            sound: true, badge: true, alert: true, provisional: true));
    _firebaseMessaging.onIosSettingsRegistered
        .listen((IosNotificationSettings settings) {
      print("Settings registered: $settings");
    });
    _firebaseMessaging.getToken().then((String token) {
      assert(token != null);
      setState(() {
        _homeScreenText = "Push Messaging token: $token";
      });
      print(_homeScreenText);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text('Push Messaging Demo'),
        ),
        // For testing -- simulate a message being received
        floatingActionButton: FloatingActionButton(
          onPressed: () => _showItemDialog(<String, dynamic>{
            "data": <String, String>{
              "id": "2",
              "status": "out of stock",
            },
          }),
          tooltip: 'Simulate Message',
          child: const Icon(Icons.message),
        ),
        body: Material(
          child: Column(
            children: <Widget>[
              Center(
                child: Text(_homeScreenText),
              ),
              Row(children: <Widget>[
                Expanded(
                  child: TextField(
                      controller: _topicController,
                      onChanged: (String v) {
                        setState(() {
                          _topicButtonsDisabled = v.isEmpty;
                        });
                      }),
                ),
                FlatButton(
                  child: const Text("subscribe"),
                  onPressed: _topicButtonsDisabled
                      ? null
                      : () {
                          _firebaseMessaging
                              .subscribeToTopic(_topicController.text);
                          _clearTopicText();
                        },
                ),
                FlatButton(
                  child: const Text("unsubscribe"),
                  onPressed: _topicButtonsDisabled
                      ? null
                      : () {
                          _firebaseMessaging
                              .unsubscribeFromTopic(_topicController.text);
                          _clearTopicText();
                        },
                ),
              ])
            ],
          ),
        ));
  }

  void _clearTopicText() {
    setState(() {
      _topicController.text = "";
      _topicButtonsDisabled = true;
    });
  }
}

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  FirebaseApp app = await Firebase.initializeApp();
  assert(app != null);
  runApp(
    MaterialApp(
      home: PushMessagingExample(),
    ),
  );
}

flutter doctor -v

[✓] Flutter (Channel stable, 1.22.0, on Mac OS X 10.15.7 19H2, locale en-GB)
    • Flutter version 1.22.0 at /Users/tahatesser/Code/flutter_stable
    • Framework revision d408d302e2 (7 days ago), 2020-09-29 11:49:17 -0700
    • Engine revision 5babba6c4d
    • Dart version 2.10.0

 
[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/tahatesser/Code/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/tahatesser/Code/sdk
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.0.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.0.1, Build version 12A7300
    • CocoaPods version 1.10.0.rc.1

[✓] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 50.0.1
    • Dart plugin version 193.7547
    • Java version OpenJDK Runtime Environment (build
      1.8.0_242-release-1644-b3-6222593)

[✓] VS Code (version 1.49.3)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.15.0

[✓] Connected device (1 available)
    • RMX2001 (mobile) • EUYTFEUSQSRGDA6D • android-arm64 • Android 10 (API 29)

• No issues found!

[Abion47]

@TahaTesser I will try it, but I'm not sure what will change. The FcmDartService#start channel method still won't exist in the iOS codebase. You can even search the repository here and see that the text "FcmDartService#start" only appears in 4 places: two Java files, one Dart file, and the changelog file.

[TahaTesser]

Hi @Abion47
Can you please provide your flutter run --verbose and a complete reproducible minimal code sample
Thank you

[Abion47]

Well... sure, but again, I don't see how this addresses the fact that the issue appears to be in the firebase_messaging codebase. I mean, think about it. If the text "FcmDartService#start" doesn't appear anywhere in this repository within an iOS native code file, then how can that channel method exist in iOS? And how would it not existing be the fault of my Flutter installation?

`flutter doctor -v`

[✓] Flutter (Channel stable, 1.22.0, on Mac OS X 10.15.7 19H2, locale en-US)
• Flutter version 1.22.0 at /Users/*************/Library/Flutter
• Framework revision d408d302e2 (10 days ago), 2020-09-29 11:49:17 -0700
• Engine revision 5babba6c4d
• Dart version 2.10.0

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
• Android SDK at /Users//Library/Android/sdk
• Platform android-29, build-tools 29.0.2
• ANDROID_HOME = /Users//Library/Android/sdk
• Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)
• All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.0.1)
• Xcode at /Applications/Xcode.app/Contents/Developer
• Xcode 12.0.1, Build version 12A7300
• CocoaPods version 1.9.3

[✓] Android Studio (version 4.0)
• Android Studio at /Applications/Android Studio.app/Contents
• Flutter plugin version 50.0.1
• Dart plugin version 193.7547
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] VS Code (version 1.50.0)
• VS Code at /Applications/Visual Studio Code.app/Contents
• Flutter extension version 3.15.0

[✓] Connected device (1 available)
• Dev iPhone (mobile) • 65301ff37867fe1b1ef12a5793125d88c193d473 • ios • iOS 13.7
! Error: Development iPad is not connected. Xcode will continue when Development iPad is connected. (code -13)

• No issues found!