Firebase Firestore get data from collection

Try this..Working fine.Below function will get Realtime Updates from firebse as well..

db = FirebaseFirestore.getInstance();


        db.collection("dynamic_menu").addSnapshotListener(new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {

                if (e !=null)
                {

                }

                for (DocumentChange documentChange : documentSnapshots.getDocumentChanges())
                {
                 String   isAttendance =  documentChange.getDocument().getData().get("Attendance").toString();
                 String  isCalender   =  documentChange.getDocument().getData().get("Calender").toString();
                 String isEnablelocation = documentChange.getDocument().getData().get("Enable Location").toString();

                   }
                }
        });

More reference :https://firebase.google.com/docs/firestore/query-data/listen

If You do not want realtime updates refer Below Document

https://firebase.google.com/docs/firestore/query-data/get-data

The get() operation returns a Task<> which means it is an asynchronous operation. Calling getListItems() only starts the operation, it does not wait for it to complete, that's why you have to add success and failure listeners.

Although there's not much you can do about the async nature of the operation, you can simplify your code as follows:

private void getListItems() {
    mFirebaseFirestore.collection("some collection").get()
            .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                @Override
                public void onSuccess(QuerySnapshot documentSnapshots) {
                    if (documentSnapshots.isEmpty()) {
                        Log.d(TAG, "onSuccess: LIST EMPTY");
                        return;
                    } else {
                        // Convert the whole Query Snapshot to a list
                        // of objects directly! No need to fetch each
                        // document.
                        List<Type> types = documentSnapshots.toObjects(Type.class);   

                        // Add all to your list
                        mArrayList.addAll(types);
                        Log.d(TAG, "onSuccess: " + mArrayList);
                    }
            })
            .addOnFailureListener(new OnFailureListener() {
                @Override
                public void onFailure(@NonNull Exception e) {
                    Toast.makeText(getApplicationContext(), "Error getting data!!!", Toast.LENGTH_LONG).show();
                }
            });
}