Opening Android app using notification & getLaunchIntentForPackage doesn't go through LauncherActivity

Question

I am using Firebase (FCM) to show Push Notifications to the user and I am running into a weird problem.

The code I have works for the following scenarios (using FirebaseMessagingService):

• App in foreground - Receiving data in onReceive() and showing a popup inside app.
• App in background - Receiving data in onReceive() and showing a notification for the user. If this is clicked the app will be brought back to front. The intent from this is received in LauncherActivity followed by a finish() call which takes me to whatever activity I already had open.
• App completely closed - same as background. App will be started and intent will be handled in LauncherActivity before calling finish() on that.

And here is where it gets interesting:

• App completely closed -> open it through notification (intent received in LauncherActivity) -> put the app in background and send another notification -> when this notification is clicked the LauncherActivity is completely ignored (onCreate is no longer called) and I get taken straight to whatever activity I already had. The intent here has no extras or categories. Why is LauncherActivity being bypassed in this specific case? Keep in mind that this works fine if the app was initially started normally (not by clicking on a notification)

Intent mainIntent = getPackageManager().getLaunchIntentForPackage(getPackageName()); 
if (mainIntent != null) {
    mainIntent.addCategory(NOTIFICATION_CATEGORY);
    mainIntent.putExtra(.........);
}
PendingIntent pendingMainIntent = PendingIntent.getActivity(this, SERVICE_NOTIFICATION_ID, mainIntent, PendingIntent.FLAG_UPDATE_CURRENT);

NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(context, context.getString(R.string.default_notification_channel_id));
notificationBuilder.setContentIntent(pendingMainIntent);
//.....icon, color, pririty, autoCancel, setDefaults, setWhen, setShowWhen, contentText, setStyle

NotificationManager notificationManager = (NotificationManager) this.getSystemService(Context.NOTIFICATION_SERVICE);
if (notificationManager != null) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        NotificationChannel channel = new NotificationChannel(
            getString(R.string.default_notification_channel_id),
            getString(R.string.default_notification_channel),
            NotificationManager.IMPORTANCE_HIGH
        );
        notificationManager.createNotificationChannel(channel);
        notificationBuilder.setChannelId(getString(R.string.default_notification_channel_id));
    }
    notificationManager.notify(SERVICE_NOTIFICATION_ID, notificationBuilder.build());
}

I'd appreciate any ideas. Thank you.

Answer 1

When you launch an app for the first time, Android remembers the Intent that was used to launch it. Normally, when you launch an app from the HOME screen, this is an Intent that contains ACTION=MAIN and CATEGORY=LAUNCHER. If your app then goes to the background (for whatever reason), and the user later taps the icon on the HOME screen, the same launch Intent is used. Android matches this against the Intent used to launch the app for the first time, and if these match, Android doesn't launch a new Activity, it just brings the task containing the app from the background to the foreground in whatever state it was in when it got moved to the background. Under normal circumstances, this is exactly the behaviour that you want (and that the user expects).

However, when the app is launched for the first time from a Notification, this can mess things up. In your case, this is what you are seeing. You launch the app from a Notification and Android remembers the Intent used (from the Notification), when you later launch the app (again from a Notification), android matches the Intent in the Notification with the Intent used to launch the app for the first time, and thinks you want to bring the existing app task from the background to the foreground.

There are several ways to deal with this, depending on the behaviour that you want to have. The best thing to do is probably not to launch your root Activity (the one with ACTION=MAIN and CATEGORY=LAUNCHER) from the Notification. Instead launch a different Activity and have that Activity determine what it should do next (ie: redirect to the root Activity or something else, depending on the state of your app). You should also set the NO_HISTORY and EXCLUDE_FROM_RECENTS flags on the Intent that you put in the Notification. This will ensure that Android won't remember this Intent as the one that launched the app.