How to Implement Firestore Pagination with RecyclerView in Android?

Firestore Pagination with RecyclerView for Android

Pagination is a crucial technique used to display large datasets efficiently and improve user experience. In Firestore, pagination can be achieved by combining query cursors and the limit() method.

Solution:

To paginate Firestore data in a RecyclerView, follow these steps:

1. Define the global variables:

   • limit (int): Set a limit to the number of documents loaded per page (e.g., 15).
   • lastVisible (DocumentSnapshot): Represents the last visible document from a query page.
   • isScrolling, isLastItemReached (boolean): Flags to track scrolling and the completion of the last page.

2. Obtain the initial query:

   • Construct a Firestore query ordered by a field (e.g., "productName").
   • Apply the limit to the query (e.g., .limit(limit)).

3. Get the initial batch of documents:

   • query.get().addOnCompleteListener() retrieves the first page of documents from the query.
   • Parse the documents into your model class (e.g., ProductModel).
   • Add the documents to the RecyclerView adapter list.

4. Implement scrolling pagination:

   • Attach a RecyclerView.OnScrollListener to the RecyclerView.
   • In onScrolled(), check if the user has reached the end of the current page and if more pages remain to be loaded.
   • If so, create a new query starting after the lastVisible document and apply the limit again.
   • Fetch the next page of documents and update the adapter.

5. Handle the last page:

   • Check the size of the last page fetched. If it's less than the limit, set isLastItemReached to true to indicate the end of the dataset.

Example Code:

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference productsRef = rootRef.collection("products");
Query query = productsRef.orderBy("productName", Query.Direction.ASCENDING).limit(limit);

query.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
    @Override
    public void onComplete(@NonNull Task<QuerySnapshot> task) {
        if (task.isSuccessful()) {
            for (DocumentSnapshot document : task.getResult()) {
                ProductModel productModel = document.toObject(ProductModel.class);
                list.add(productModel);
            }
            productAdapter.notifyDataSetChanged();
            lastVisible = task.getResult().getDocuments().get(task.getResult().size() - 1);

            RecyclerView.OnScrollListener onScrollListener = new RecyclerView.OnScrollListener() {
                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    LinearLayoutManager linearLayoutManager = ((LinearLayoutManager) recyclerView.getLayoutManager());
                    int firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition();
                    int visibleItemCount = linearLayoutManager.getChildCount();
                    int totalItemCount = linearLayoutManager.getItemCount();

                    if (isScrolling &amp;&amp; (firstVisibleItemPosition + visibleItemCount == totalItemCount) &amp;&amp; !isLastItemReached) {
                        isScrolling = false;
                        Query nextQuery = productsRef.orderBy("productName", Query.Direction.ASCENDING).startAfter(lastVisible).limit(limit);
                        nextQuery.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                            @Override
                            public void onComplete(@NonNull Task<QuerySnapshot> t) {
                                if (t.isSuccessful()) {
                                    for (DocumentSnapshot d : t.getResult()) {
                                        ProductModel productModel = d.toObject(ProductModel.class);
                                        list.add(productModel);
                                    }
                                    productAdapter.notifyDataSetChanged();
                                    lastVisible = t.getResult().getDocuments().get(t.getResult().size() - 1);

                                    if (t.getResult().size() < limit) {
                                        isLastItemReached = true;
                                    }
                                }
                            }
                        });
                    }
                }
            };
            recyclerView.addOnScrollListener(onScrollListener);
        }
    }
});

By following these steps, you can implement efficient and real-time pagination for Firestore data in your Android application.

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