How to detect data is added in firestore during offline android app

Question

I'm working with firestore in android. I want to allow my user to save the data in app during the offline mode.(Data insertion during offline is also working fine) But I don't know how I can detect that data is added in offline mode, I need to get document id that is added. In the online mode I can detect the data insertion with the listener as.

Map<String, Object> data = new HashMap<>();
data.put("name", "Tokyo");
data.put("country", "Japan");

db.collection("cities")
        .add(data)
        .addOnSuccessListener(new OnSuccessListener<DocumentReference>() {
            @Override
            public void onSuccess(DocumentReference documentReference) {
                Log.d(TAG, "DocumentSnapshot written with ID: " + documentReference.getId());
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Log.w(TAG, "Error adding document", e);
            }
        });

I also need to detect that is added when the app is offline. So how I can? Because these listeners only works when the data is inserted in the server and app get the response from the server.

Answer 1

The addOnSuccessListener only gets called once the data is committed to the server. That's its explicit goal. If you local client also need the data after it's added locally, you'll do that with a regular addSnapshotListener.

From the documentation on events for local changes:

Local writes in your app will invoke snapshot listeners immediately. This is because of an important feature called "latency compensation." When you perform a write, your listeners will be notified with the new data before the data is sent to the backend.

Retrieved documents have a metadata.hasPendingWrites property that indicates whether the document has local changes that haven't been written to the backend yet. You can use this property to determine the source of events received by your snapshot listener.

See the linked documentation for sample code of how to process this.

Update: if you're just trying to get the ID of a new document, you can simply do:

DocumentReference newDoc = db.collection("cities").document();
System.out.println(newDoc.getId());
newDoc.set(data);

See CollectionReference.document().

Answer 2

Offline insert listener. Based on my code test, it is just fine to remove both the success and snapshot listeners. simply check if a document id is not null and its length is greater than 10. that was enough for me to conclude a successful insert. code :

 docRef.collection("collectioname").document("docname").set(aMap);
  String id = docRef.collection("collectioname").document("docname").getId();
            if( id != null & !id.isEmpty() & id.length() > 10) {
                //Action here
             }

Thank you Frank for your earlier clue. The add() will always write the document to the local .....in my case the set() method.