Firebase android pagination load always same items

问题:

I'm trying to do a pagination in firebase. I've followed this approach (Firebase pagination limitToFirst() vs limitToLast()) but I can't get a correct pagination items from firebase, always get the same 3 items.

This is the problem with the code below:

I have 12 items in my firebase database. I retrieve the 3 elements with the first load items, and when I try to load more items, I always get the same elements that I got in the first load.

I've tried with: postList.size()-1).getTimestamp().toString()
and postList.size()-3).getTimestamp().toString() but always get the same data

private ArrayList<Post> postList = new ArrayList<>();
private Query allPostsQuery;
private final static int PAGESIZE = 3;

//First load items when start

linearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(linearLayoutManager);
mAdapter = new WallAdapter(postList, getFragmentManager(), getActivity(), navigation, mListener, WallFragmentOwn.this);
mRecyclerView.setAdapter(mAdapter);
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        if(dy > 0) {
            visibleItemCount = linearLayoutManager.getChildCount();
            totalItemCount = linearLayoutManager.getItemCount();
            pastVisiblesItems = linearLayoutManager.findFirstVisibleItemPosition();

            if (loading) {
                if ((visibleItemCount + pastVisiblesItems) >= totalItemCount) {
                    loading = false;
                    loadMoreItems();
                }
            }
        }
    }
});

//Load more

public void loadMoreItems(){
            allPostsQuery = FirebaseUtil.getPostsRef().orderByChild("timestamp")
                        .endAt(postList.get(postList.size()-1).getTimestamp().toString())
                        .limitToLast(PAGESIZE);
            allPostsQuery.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {

                    if(dataSnapshot.getValue() == null){
                        return;
                    }
                    dataSnapshot.getChildrenCount();
                    for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
                        Post post = postSnapshot.getValue(Post.class);
                        post.setUid(postSnapshot.getKey());
                        postList.add(post);
                    }
                    mAdapter.notifyDataSetChanged();
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });

        }

UPDATE 1 I understand that I need to do the .endAt() with the same type that I have in Firebase database. This is my code know:

//POJO CLASS

      private HashMap<String, Object> timestampCreated;


public Post(String text, HashMap<String, Object>  timestampCreatedObj) {
    this.text = text;
    timestampCreatedObj = new HashMap<String, Object>();
    timestampCreatedObj.put("date", ServerValue.TIMESTAMP);
    this.timestampCreated = timestampCreatedObj;

}

 @Exclude
    public long getCreatedTimestampLong(){
        return (long)timestamp;
    }

My Query:

allPostsQuery = getBaseRef().child("posts").orderByChild("timestamp")
            .endAt(postList.get(postList.size()-1).getTimestampCreatedLong())
            .limitToFirst(PAGESIZE);

I Set the timestamp in Firebase in this way:

      HashMap<String, Object> timestamp = new HashMap<String, Object>();
    timestamp.put("timestamp", ServerValue.TIMESTAMP);

    Post newPost = new Post(postText, timestamp);
    postsRef.push().setValue(newPost);

JSON FIREBASE

{
  "-Kt8GeVfyiebF8XhUUkL" : {
    "text" : "0",
    "timestampCreated" : {
      "date" : 1504467921811
    }
  }
}

UPDATE 2

Change the tag inside orderByChild and know, is working pagination.

orderByChild("timestampCreated/date")