In my Android app I need my app to get notified when some file (a picture file) gets renamed, something like a ContentObserver, but I need my app to be notified even when it's closed, so I would need something like a BroadcastReceiver. My app knows the paths of the folders it wants to listen to.
Do you know any way to do it?
There is nothing in Android that will notify you of arbitrary filesystem operations, except
FileObserver, which requires your process to be running. In particular, Android does not issue a system broadcast for arbitrary filesystem operations, in large part due to the massive overhead that this would introduce.