Reacting to activity lifecycle in ViewModel

I'm trying to create an app which will use MVVM architecture and there's one thing I quite don't understand.

Official Android docs say that's not a good idea to reference activity context in ViewModel's (as ViewModel may outlive activity) so I've started to wonder about usecase when I want to execute some action when my activity is resumed.

I know ViewModel's shouldn't do business logic themselves but even if I use some service class (let's say GPSService which has to start and pauseeach time activity is resumed on paused), and inside this service I react to activity onResume (using Lifecycle observer) I will still reference this activity from ViewModel as I'm referencing service which holds reference to activity being observed, this may cause activity leak (correct me if I'm wrong).

So my question is, how to react to activity or fragment lifecycle in MVVM architecture?

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