Stop background sync when network connection is lost

[dontub]

The F-Droid version of Element periodically tries to perform a background sync no matter whether a network connection is available or not. To reduce battery usage #536 the background sync should be stopped when no network connection is available. As far as I can see there are at least two ways to achieve this:

1. Using a PeriodicWorkRequest with NetworkType.CONNECTED as constraint. https://developer.android.com/topic/libraries/architecture/workmanager/how-to/define-work Edit: A PeriodicWorkRequest cannot run more often then every 15 minutes.

2. Using a ConnectivityManager.NetworkCallback to be informed when a network connection is available or a network connection is lost. https://developer.android.com/reference/android/net/ConnectivityManager.NetworkCallback

[dontub]

Instead of using a PeriodicWorkRequest it is possible to use an OneTimeWorkRequest with initial delay: https://github.com/luki-ev/synod-android/blob/stop-background-sync-when-connection-not-available/vector/src/fdroid/java/im/vector/app/push/fcm/worker/BackgroundSyncWorker.kt

No battery usage without network using that code 🙂