Handling keepSynced() while on background on Android and with FCM

I'm considering the use of keepSynced() for some data from Firebase Realtime Database. I understand that it will automatically sync those paths. But how does that relate to Android lifecycle? If the user leaves all activities (and all normal listeners disconnect), will it stop syncing? I don't want the app to become data or battery hog.

On the other hand, I would like to update cached data when FCM notification arrives. I can launch some service which will connect to Firebase. I would like to sync all paths which are in keepSynced() and stop it when it's synced. I'm not sure how to achieve that. Create a listener to one of the paths and keep the service running for some time? After the service is finished, will it stop syncing?

Solution 1:

firebaser here

Great question!

When there is no active activity, the operating system may close the connection to the Firebase database at any time. Our SDKs don't try to prevent that, but will reconnect when the app becomes active again.

What you're describing in your second paragraph is what we call "push to sync", where you send a push notification (typically a silent FCM data message) to trigger synchronizing of the data.

We did something like that in last year's I/O app and, while it was a bit more complex than we wanted it to be, it worked great. We explicitly managed the connection in that case, calling goOnline() and goOffline() (after 5 minutes iirc). The main sync code can be found in the IOSched github repo.