Firestore.getInstance(): how to use?

Question

Firebase Firestore provides the getInstance() method, which opens a socket (only one, at any time of execution of the app) and instanciates the Firestore client.

I would want to query and store data, using or not listeners (to get realtime updates, etc.). If I call getInstance as soon as I need to query or store, or if I store this instance in a static class when my app starts and then use this static class attribute as soon as I need to query or store: these 2 cases are technically the same. Because Google uses singleton pattern (getInstance()).

But am I missing something? Is it actually safe to store this instance as a static class attribute, and use it when I need it? And is it really safe to call getInstance whenever I need it? To be more explicit: between 2 calls to getInstance() (or between 2 accesses to the static class attribute), i.e.: between 2 points of execution time, is there any risk to loose network connection, socket connection, realtime listeners (snapshots) connection, etc. ?

If yes: How to handle these problem(s)?

Answer 1

To complement Alex Mamo's answer, and avoid repeating FirebaseFirestore.getInstance() everywhere, I declared a static method called db which returns the result of the getInstance :

public static FirebaseFirestore db(){
    return FirebaseFirestore.getInstance();
};

Then I use it like that :

db().collection(...)

Answer 2

I would want to query and store data, using or not listeners (to get realtime updates, etc.)

There is no way to get data or even get realtime updates without using a listener. Everything in Cloud Firestore is about listeners.

if I store this instance in a static class when my app starts and then use this static class attribute as soon as I need to query or store

Do not place Android context classes in static fields. Static reference to FirebaseFirestore which has field context pointing to Context will lead to a memory leak.

A static field will leak contexts. Non-static inner classes have an implicit reference to their outer class. If that outer class is for example a Fragment or Activity, then this reference means that the long-running handler/loader/task will hold a reference to the activity which prevents it from getting garbage collected.

So instead of storing it as a static variable call getInstance() whenever is needed. Or a more convenient solution would to use dependency injection. Dagger can help you solve that.

And is it really safe to call getInstance whenever I need it?

Yes it is.

between 2 accesses to the static class attribute), i.e.: between 2 points of execution time, is there any risk to loose network connection, socket connection, realtime listeners (snapshots) connection, etc. ?

Please see explanation above.