How to Efficiently Paginate Firestore Data for Android RecyclerView Scrolling?

Paginating Firestore Data for Android RecyclerView with Scrolling

Problem Description

Firestore documentation provides limited guidance on implementing pagination with RecyclerView for scrolling scenarios. Despite following the official documentation, users may encounter difficulties.

Solution: Pagination with OnScrollListener

To paginate data from Firestore and display it in a RecyclerView progressively, follow these steps:

1. Set up the RecyclerView: Configure the layout manager and instantiate the RecyclerView with an empty list adapter.
2. Define the Firestore query: Use the orderBy() and limit() methods to retrieve items in ascending order with a limit (e.g., 15).
3. Initial query execution: Perform the initial query and add the retrieved data to the list adapter. Update lastVisible to represent the last visible document.
4. RecyclerView scroll listener: Add a RecyclerView.OnScrollListener to the RecyclerView to detect when the user is approaching the end of the list.
5. Pagination logic: If scrolling is detected and the end of the list is not reached, perform a new query using startAfter(lastVisible). Add the retrieved data to the list adapter and update lastVisible.
6. Check for last item: If the new query returns fewer than the specified limit, mark that the last item has been reached and disable further pagination.

Code Example

// ...

// Define the query limit
private val limit = 15

// Initial query
val query = productsRef.orderBy("productName", Query.Direction.ASCENDING).limit(limit)

query.get().addOnCompleteListener { task ->
    if (task.isSuccessful) {
        for (document in task.result!!) {
            val productModel = document.toObject(ProductModel::class.java)
            list.add(productModel)
        }
        productAdapter.notifyDataSetChanged()
        lastVisible = task.result!!.documents[task.result!!.size() - 1]

        // RecyclerView scroll listener
        recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
                super.onScrollStateChanged(recyclerView, newState)
                if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
                    isScrolling = true
                }
            }

            override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
                super.onScrolled(recyclerView, dx, dy)

                val linearLayoutManager = recyclerView.layoutManager as LinearLayoutManager
                val firstVisibleItemPosition = linearLayoutManager.findFirstVisibleItemPosition()
                val visibleItemCount = linearLayoutManager.childCount
                val totalItemCount = linearLayoutManager.itemCount

                if (isScrolling && (firstVisibleItemPosition + visibleItemCount == totalItemCount) && !isLastItemReached) {
                    isScrolling = false
                    val nextQuery =
                        productsRef.orderBy("productName", Query.Direction.ASCENDING).startAfter(lastVisible).limit(limit)
                    nextQuery.get().addOnCompleteListener { t ->
                        if (t.isSuccessful) {
                            for (d in t.result!!) {
                                val productModel = d.toObject(ProductModel::class.java)
                                list.add(productModel)
                            }
                            productAdapter.notifyDataSetChanged()
                            lastVisible = t.result!!.documents[t.result!!.size() - 1]

                            if (t.result!!.size() < limit) {
                                isLastItemReached = true
                            }
                        }
                    }
                }
            }
        })
    }
}

// ...

Conclusion

The provided solution efficiently handles pagination for RecyclerView in a scrolling scenario. It ensures timely data retrieval as the user scrolls, providing a seamless loading experience.

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