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:
-
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.
-
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)).
-
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.
-
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.
-
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 && (firstVisibleItemPosition + visibleItemCount == totalItemCount) && !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() <p>By following these steps, you can implement efficient and real-time pagination for Firestore data in your Android application.</p></querysnapshot></querysnapshot></querysnapshot></querysnapshot>
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