How to bypass the Firebase cache to refresh data?

Question

On an Android application which must works offline most of the time I need, when it's online, to do some synchronous operations but Firebase always take the value from the cache when I need the value in the servor , Here a exemple

Query query = FirebaseDatabase.getInstance().getReference()
        .child("Post")
        .child(UserChannel)
        .child("Post");
query.keepSynced(false);

query.addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        if(dataSnapshot.exists()){
            Log.d(TAG, "Posts founded" );

            for(DataSnapshot snapshot: dataSnapshot.getChildren()){
                Posts thepost= snapshot.getValue(Posts.class);

                Log.d(TAG, "Post found");  

                ListPosts.add(thepost);
            }
        }else {
            Log.d(TAG, "  no post could be found.");              
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        throw databaseError.toException(); // don't ignore errors
    }
});

Here I use addListenerForSingleValueEvent for load posts from a specific user , it works fine but if the user add a new post in the child and I try to reload all his posts , the new post wont be loaded . I assume Firebase load the post from the cache how can I bypass this the cache to load only from servor ?

`addListenerForSingleValueEvent` will return the latest value from the cache, and then refresh that cache with data from the server. If you call `keepSynced` in time, it will ensure the cache is up to date, but you might have a race condition here - in that the cache hasn't been updated yet when you call `addListenerForSingleValueEvent`. The solution is always the same: don't mix `addListenerForSingleValueEvent` with disk peristence, but use `addValueEventListener` and be prepared for multiple calls to `onDataChange`. See https://stackoverflow.com/a/34487195 — Frank van Puffelen, Aug 25 '20 at 19:59

score 3 · Answer 1 · answered Aug 26 '20 at 17:07

If you want your app to get data when a new child it's added use the following

        databaseReference.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
            
        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

        }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot snapshot) {

        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });

Inside the onChildAdded add what you want to happen when a child it's added. Be aware that onChildAdded gets the initial data and then will trigger again for last child added. For additional information check this

How to bypass the Firebase cache to refresh data?

1 Answers1