title: When to use getActivity in addSnapshotListener?
body: <p>When to use <code>getActivity</code> and <code>this</code> or <code>Executor</code> in addSnapshotListener .
  I read <a href="https://developers.google.com/android/reference/com/google/firebase/firestore/Query#addSnapshotListener(com.google.firebase.firestore.MetadataChanges,%20com.google.firebase.firestore.EventListener%3Ccom.google.firebase.firestore.QuerySnapshot%3E)" rel="nofollow noreferrer">documentation</a> and still not clearly understand.<a href="https://i.stack.imgur.com/rCRX4.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rCRX4.jpg" alt="enter image description here"></a></p>