How to make Paging library work with reverse recyclerview?

Question

How to use the latest paging with endless reverse recyclerview for the purpose of chat?

I have linear layout with reverse layout true:

LinearLayoutManager layoutManager = new LinearLayoutManager(this);
layoutManager.setReverseLayout(true);
layoutManager.setStackFromEnd(true);

and inside scroll listener :

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    super.onScrolled(recyclerView, dx, dy);
    int visibleItemCount = layoutManager.getChildCount();
    int totalItemCount = layoutManager.getItemCount();
    int firstVisibleItemPosition = layoutManager.findFirstVisibleItemPosition();

    if (!isLoading && !isLastPage) {
        if ((visibleItemCount + firstVisibleItemPosition) >= totalItemCount
                && firstVisibleItemPosition >= 0
                && totalItemCount >= PAGE_SIZE) {
            loadMoreItems();
        }
    }
}

The query for fetching messages:

SELECT * FROM Message WHERE chatId = :chatId ORDER BY dbId ASC

Used for the room like below;

@Query("SELECT * FROM Message WHERE chatId = :chatId ORDER BY dbId ASC")
DataSource.Factory<Integer,Message> fetchAll(String chatId);

The problem is that if I use ASC in the query, the list is automatically scrolling and fetching other messages. if used DESC, then message list is not coming in order.

Can anyone please help?

Answer 1

I think it's enogh

layoutManager.setStackFromEnd(false);

---

layoutManager.setReverseLayout(true);

If you have an incremental list in room database (line an index/contor) you can sort it after it in DESC mode

Answer 2

It may be late but yes I too was making a chat application where the chat should open at the bottom and the person can scroll up to see old messages. I have used room DB to store chat messages and used the pagination library for pagination. For this functionality to achieve you have to use only

`app:reverseLayout="true"`

and use room datasource factory with the following command to fetch the data -

    @Query("SELECT * from table_name ORDER BY timestamp DESC")

Here order by desc is very important. The timestamp is the field in the database table. And u don't need scroll listener with pagination library. It automatically handles the scrolling listeners. For the whole project refer this - https://bitbucket.org/raghavsharma29/chatbotmvvm/src/dev/