Flutter: Push notifications even if the app is closed

For reminders i would recomend Flutter Local Notifications Plugin. It has a powerful scheduling api. From the documentation of local notification:

Scheduling when notifications should appear - Periodically show a notification (interval-based) - Schedule a notification to be shown daily at a specified time - Schedule a notification to be shown weekly on a specified day and time - Ability to handle when a user has tapped on a notification when the app is the foreground, background or terminated

And for push notification, you can use Firebase Cloud Messaging or one signal plugin or you can implement natively through platform-channels

Edit: You can also fire notifications according to specific conditions even if the app is terminated. This can be achevied by running dart code in the background. Quoting from the official faq:

Can I run Dart code in the background of an Flutter app? Yes, you can run Dart code in a background process on both iOS and Android. For more information, see the Medium article Executing Dart in the Background with Flutter Plugins and Geofencing.

I have found a solution to this problem. We just have to register the Local Notification Plugin in the Application class.

First Create a class FlutterLocalNotificationPluginRegistrant, I have created this in Kotlin.

class FlutterLocalNotificationPluginRegistrant {

companion object {
    fun registerWith(registry: PluginRegistry) {
        if (alreadyRegisteredWith(registry)) {
            Log.d("Local Plugin", "Already Registered");
            return
        }
        FlutterLocalNotificationsPlugin.registerWith(registry.registrarFor("com.dexterous.flutterlocalnotifications.FlutterLocalNotificationsPlugin"))
        Log.d("Local Plugin", "Registered");
    }

    private fun alreadyRegisteredWith(registry: PluginRegistry): Boolean {
        val key = FlutterLocalNotificationPluginRegistrant::class.java.canonicalName
        if (registry.hasPlugin(key)) {
            return true
        }
        registry.registrarFor(key)
        return false
    }
}}

Now create a Application class extending FlutterApplication and implement PluginRegistry.PluginRegistrantCallback.

class Application : FlutterApplication(), PluginRegistry.PluginRegistrantCallback {

override fun onCreate() {
    super.onCreate()
}

override fun registerWith(registry: PluginRegistry?) {
    if (registry != null) {
        FlutterLocalNotificationPluginRegistrant.registerWith(registry)
    }
}}

and register the Application class in the AndroidManifest.xml

<application
    android:name="com.packagename.Application"/>

All done. Now write a function to show notification and call it from the background handler method of Firebase messaging.

    Future _showNotificationWithDefaultSound(String title, String message) async {
  var androidPlatformChannelSpecifics = AndroidNotificationDetails(
      'channel_id', 'channel_name', 'channel_description',
      importance: Importance.Max, priority: Priority.High);
  var iOSPlatformChannelSpecifics = IOSNotificationDetails();
  var platformChannelSpecifics = NotificationDetails(
      androidPlatformChannelSpecifics, iOSPlatformChannelSpecifics);
   await flutterLocalNotificationsPlugin.show(
    0,
    '$title',
    '$message',
    platformChannelSpecifics,
    payload: 'Default_Sound',
  );
}

and call it like this.

    Future<dynamic> myBackgroundMessageHandler(Map<String, dynamic> message) async {

  if (message['data'] != null) {
    final data = message['data'];

    final title = data['title'];
    final body = data['message'];

    await _showNotificationWithDefaultSound(title, message);
  }
  return Future<void>.value();
}

I have also faced this issue, So these are my learnings

In my Case : i am able to get notification in App-Resume or App-background state, but in App-Close state, I am not receiving notifification.

In this case our notification body was :

{notification: {body: null, title: null}, data: {body: hello, title: world}}

To Receive Notification in App-Closed state we changed notification to

{notification: {body: abc, title: abc}, data: {url: string, body: string, title: string}}