Firebase Firestore在应用启动时检索数据，而不是保存数据

Question

I got an issue on my Android app that makes it get information from the Firestore Database every time the application is loaded. In the Firebase Docs, they say that persistence is enabled by default, but that seems not to work for me. Tried to add the settings but nothing changed.

FirebaseFirestoreSettings settings = new FirebaseFirestoreSettings.Builder()
            .setPersistenceEnabled(true)
            .build();
    db.setFirestoreSettings(settings);

The query inside onCreate:

db.collection("administradores").whereEqualTo("email", user.getEmail()).get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            for (DocumentSnapshot document : task.getResult()) {
                                tipo = (long) document.getData().get("tipo");
                                if (tipo == HomeFragment.EVENTO_CODE){
                                    menu.findItem(R.id.nav_nuevo).setTitle("Nuevo evento");
                                    menu.findItem(R.id.nav_editar).setTitle("Tus eventos");
                                    fragment.tipoEmpresa.setText("Administrador de eventos");
                                    fragment.tusEvLoc.setText("Tus eventos");
                                }else if(tipo == HomeFragment.COMERCIO_CODE){
                                    menu.findItem(R.id.nav_nuevo).setTitle("Nuevo local");
                                    menu.findItem(R.id.nav_editar).setTitle("Tus tiendas");
                                }else if(tipo == HomeFragment.BAR_CODE){
                                    menu.findItem(R.id.nav_nuevo).setTitle("Nuevo local");
                                    menu.findItem(R.id.nav_editar).setTitle("Tus establecimientos");
                                }
                            }
                        }
                    }
                });

I am expecting the data to be saved (downloaded) only once, and be updated when there are changes in the database. May this work with the Firestore tools or is it necessary to create an internal database (ie SQLite) to save all the data?

Answer 1

use this to get data from cache. if you want to manually save the data you would need to store it in a local database and work out a way to keep the data synced in your local database. the addSnapshotListener runs when any document is added modified or removed in the collection.

db.collection("cities").whereEqualTo("state", "CA")
    .addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(@Nullable QuerySnapshot querySnapshot,
                            @Nullable FirebaseFirestoreException e) {
            if (e != null) {
                Log.w(TAG, "Listen error", e);
                return;
            }

            for (DocumentChange change : querySnapshot.getDocumentChanges()) {
                if (change.getType() == Type.ADDED) {
                    Log.d(TAG, "New city:" + change.getDocument().getData());
                }

                String source = querySnapshot.getMetadata().isFromCache() ?
                        "local cache" : "server";
                Log.d(TAG, "Data fetched from " + source);
            }

        }
    });