Run Android Native code in background / terminated app

[LuisCampos97]

Hi!
I have an application that receives notifications through firebase_messaging, and I needed to build my customizable notification to display.
For this I created native Android code. When I receive the push notification in foreground, I can show the notification without problems, the problem is when I receive the notification in the background it gives an error:
Unhandled Exception: MissingPluginException(No implementation found for method showNotification on channel channel.luis/notifications)

Android Native Code:

public class MainActivity extends FlutterFragmentActivity {

    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
        super.configureFlutterEngine(flutterEngine);

        new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), "channel.luis/notifications").setMethodCallHandler(
                (call, result) -> {
                    if(call.method.equals("showNotification")) {
                        showNotification(call);
                    } else {
                        result.notImplemented();
                    }
                }
        );
    }

Flutter Code

_messaging.configure(
        onBackgroundMessage: Platform.isIOS ? null : onBackgroundMessageHandler,

        //* When app is in foreground (open)
        onMessage: (Map<String, dynamic> message) async {
          NotificationHandler.showNotification(message['data']);
        },

        //* When app is in background
        onResume: (Map<String, dynamic> message) async {},

        //* When app is closed
        onLaunch: (Map<String, dynamic> message) async {});
  }

  static Future onBackgroundMessageHandler(Map<String, dynamic> message) {
    if (message['data'] != null) {
      dynamic data = message['data'];

      NotificationHandler.showNotification(Map<String, dynamic>.from(data));
    }

    return Future<void>.value();
  }

static void showNotification(var message) async {
    const channel = MethodChannel('channel.luis/notifications');

    channel.invokeMethod('showNotification', {
      "title": message['title'],
      "description": message['body'],
      "type": message['ntfType'],
    });
  }

The showNotification of the onMessage method works without problems and shows the customizable notification I made with native Android code. The problem when the push notification arrives in the background in the onBackgroundMessageHandler method it shows the Unhandled Exception: MissingPluginException errorI showed above.

Can someone help me please?

Flutter Doctor -v

[✓] Flutter (Channel stable, 1.22.6, on Linux, locale en_US.UTF-8)
    • Flutter version 1.22.6 at /home/luis/snap/flutter/common/flutter
    • Framework revision 9b2d32b605 (5 weeks ago), 2021-01-22 14:36:39 -0800
    • Engine revision 2f0af37152
    • Dart version 2.10.5

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at /home/luis/android-sdk
    • Platform android-30, build-tools 29.0.2
    • ANDROID_HOME = /home/luis/android-sdk
    • Java binary at: /usr/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_282-8u282-b08-0ubuntu1~20.10-b08)
    • All Android licenses accepted.

[!] Android Studio (not installed)
    • Android Studio not found; download from https://developer.android.com/studio/index.html
      (or visit https://flutter.dev/docs/get-started/install/linux#android-setup for detailed instructions).

[✓] Connected device (1 available)
    • KB2003 (mobile) • 950b8db0 • android-arm64 • Android 11 (API 30)

Details

[TahaTesser]

Hi @LuisCampos97
Looks like you're not registering FCM in your Android code, please add something like this and check out README

Hope this helps
Can you please provide a minimal complete reproducible code sample in a repository
Thank you

[LuisCampos97]

Hi @TahaTesser ,
I had already registered FCM in Android code:

public class Application extends FlutterApplication implements PluginRegistrantCallback {
    @Override
    public void onCreate() {
        super.onCreate();
        FlutterFirebaseMessagingService.setPluginRegistrant(this);

        StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
        StrictMode.setThreadPolicy(policy);
    }

    @Override
    public void registerWith(PluginRegistry registry) {
        FirebaseMessagingPlugin.registerWith(registry.registrarFor("io.flutter.plugins.firebasemessaging.FirebaseMessagingPlugin"));
        FlutterLocalNotificationsPlugin.registerWith(registry
                .registrarFor("com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin"));
    }
}

I already tested showing notifications with FlutterLocalNotificationsPlugin and and received it in the background and with the application closed. So the problem here is not that of FCM.

As I wanted to make customizable notifications I had to make native Android code and call through MethodChannel. The problem here is that I can't call my showNotification (called on invokeMethod) while app is in the backgroud.

[LuisCampos97]

@TahaTesser
I can print the "Receive notification in background" string when app is in background, but when I call the showNotification of the channel that I created it gives that error:

static Future onBackgroundMessageHandler(Map<String, dynamic> message) {
    if (message['data'] != null) {
      dynamic data = message['data'];

      print("Receive notification in background");

      const channel = MethodChannel('channel.luis/notifications');

      channel.invokeMethod('showNotification', {
        "title": data['title'],
        "description": data['body'],
        "type": data['ntfType'],
        "value": "123",
      });
    }

    return Future<void>.value();
  }

Console log:

I/flutter ( 4160): Receive notification in background
E/flutter ( 4160): [ERROR:flutter/lib/ui/ui_dart_state.cc(177)] Unhandled Exception: MissingPluginException(No implementation found for method showNotification on channel channel.luis/notifications)
E/flutter ( 4160): #0      MethodChannel._invokeMethod
package:flutter/…/services/platform_channel.dart:157
E/flutter ( 4160): <asynchronous suspension>
E/flutter ( 4160): #1      MethodChannel.invokeMethod
package:flutter/…/services/platform_channel.dart:332
E/flutter ( 4160): #2      FirebaseNotifications.onBackgroundMessageHandler
package:fact_mobile_app/firebase/firebase_notification_handler.dart:53
E/flutter ( 4160): #3      _fcmSetupBackgroundChannel.<anonymous closure>
package:firebase_messaging/firebase_messaging.dart:38
E/flutter ( 4160): #4      MethodChannel._handleAsMethodCall
package:flutter/…/services/platform_channel.dart:430
E/flutter ( 4160): #5      MethodChannel.setMethodCallHandler.<anonymous closure>
package:flutter/…/services/platform_channel.dart:383
E/flutter ( 4160): #6      _DefaultBinaryMessenger.handlePlatformMessage
package:flutter/…/services/binding.dart:283
E/flutter ( 4160): #7      _invoke3.<anonymous closure> (dart:ui/hooks.dart:280:15)
E/flutter ( 4160): #8      _rootRun (dart:async/zone.dart:1190:13)
E/flutter ( 4160): #9      _CustomZone.run (dart:async/zone.dart:1093:19)
E/flutter ( 4160): #10     _CustomZone.runGuarded (dart:async/zone.dart:997:7)
E/flutter ( 4160): #11     _invoke3 (dart:ui/hooks.dart:279:10)
E/flutter ( 4160): #12     _dispatchPlatformMessage (dart:ui/hooks.dart:154:5)
E/flutter ( 4160):

The app doesn't recognize my native Android code when it's in the background, I don't know why. Can you help me?

[hamdikahloun]

You need A foreground service for that.
For more information about service : https://developer.android.com/guide/components/services

For more information about Activity lifecycle : https://developer.android.com/guide/components/activities/activity-lifecycle

[LuisCampos97]

@hamdikahloun Many thanks for the reply. Can you give me some sample code to get a sense of how to do this please? Thanks!

[hamdikahloun]

See https://stackoverflow.com/questions/4360074/creating-a-service-in-android.

if you need assistance with your code please follow the link I want help writing my application in https://github.com/flutter/flutter/issues/new/choose

[LuisCampos97]

Hi @hamdikahloun ,
In the documentation it says: "A foreground service must provide a notification for the status bar, which is placed under the Ongoing heading. This means that the notification cannot be dismissed unless the service is either stopped or removed from the foreground".

I don't want a notification that can't be dismissible, I want it in the background and in real time to receive a push notification on the flutter side and launch a notification on the Android side.

[hamdikahloun]

In android, for background tasks you have to use a service.
The type of service depends on your needs.
Activity (MainActivity) are in onPause / onStop Lifecycle if you quit the application.

You can also try local notifications plugin. See local-push-notification-in-flutter

Thank you

[LuisCampos97]

Thanks @hamdikahloun.
I was able to show the notifications in the background with the local-push-notification plugin without any problems. The problem is that I wanted my own customization of the notification and it had to be through RemoteViews in the native code.

I already thought about forking the local-push-notification plugin and changing the showNotification method to my own way (since it works to show notifications in the background), but I don't know how good a idea it is.

[dubey2k]

https://developer.android.com/training/notify-user/build-notification
Try creating notification by following this link.

[LuisCampos97]

I've already managed to create a notification and show it but only when the application is in the foreground. When in background, the error I mentioned above appears.

[TahaTesser]

Hi @LuisCampos97
Please see https://flutter.dev/community for resources and asking questions like this,
you may also get some help if you post it on Stack Overflow and if you need help with your code, please see https://www.reddit.com/r/flutterhelp/
Closing, as this isn't an issue with Flutter itself. If you disagree, please write in the comments and I will reopen it.
Thank you