Pagination with Firebase firestore - swift 4 - swift

Question

I'm trying to paginate data (infinitely scroll my tableview) using firestore. I've integrated the code google gives for pagination as best I can, but I'm still having problems getting the data to load in correctly.
The initial set of data loads into the tableview as wanted. Then, when the user hits the bottom of the screen, the next "x" amount of items are load in. But when the user hits the bottom of the screen the second time, the same "x" items are simply appended to the table view. The same items keep getting added indefinitely.
So its the initial 3 "ride" objects, followed by the next 4 "ride" objects repeating forever.
123 4567 4567 4567 4567...
How do I get the data to load in correctly?
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let offsetY = scrollView.contentOffset.y
let contentHeight = scrollView.contentSize.height
if offsetY > contentHeight - scrollView.frame.height {
// Bottom of the screen is reached
if !fetchingMore {
beginBatchFetch()
}
}
}
func beginBatchFetch() {
// Array containing "Ride" objcets is "rides"
fetchingMore = true
// Database reference to "rides" collection
let ridesRef = db.collection("rides")
let first = ridesRef.limit(to: 3)
first.addSnapshotListener { (snapshot, err) in
if let snapshot = snapshot {
// Snapshot isn't nil
if self.rides.isEmpty {
// rides array is empty (initial data needs to be loaded in).
let initialRides = snapshot.documents.compactMap({Ride(dictionary: $0.data())})
self.rides.append(contentsOf: initialRides)
self.fetchingMore = false
DispatchQueue.main.asyncAfter(deadline: .now() + 5, execute: {
self.tableView.reloadData()
})
print("first rides loaded in")
}
} else {
// Error
print("Error retreiving rides: \(err.debugDescription)")
return
}
// reference to lastSnapshot
guard let lastSnapshot = snapshot!.documents.last else{
// The collection is empty
return
}
let next = ridesRef.limit(to: 4).start(afterDocument: lastSnapshot)
next.addSnapshotListener({ (snapshot, err) in
if let snapshot = snapshot {
if !self.rides.isEmpty {
let newRides = snapshot.documents.compactMap({Ride(dictionary: $0.data())})
self.rides.append(contentsOf: newRides)
self.fetchingMore = false
DispatchQueue.main.asyncAfter(deadline: .now() + 7, execute: {
self.tableView.reloadData()
})
print("new items")
return
}
} else {
print("Error retreiving rides: \(err.debugDescription)")
return
}
})
}
}

Answer 1

So here's the solution I've come up with! It is very likely that this solution makes multiple calls to firestore, creating a large bill for any real project, but it works as a proof of concept I guess you could say.
If you have any recommendations or edits, please feel free to share!
var rides = [Ride]()
var lastDocumentSnapshot: DocumentSnapshot!
var fetchingMore = false
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let offsetY = scrollView.contentOffset.y
let contentHeight = scrollView.contentSize.height
//print("offsetY: \(offsetY) | contHeight-scrollViewHeight: \(contentHeight-scrollView.frame.height)")
if offsetY > contentHeight - scrollView.frame.height - 50 {
// Bottom of the screen is reached
if !fetchingMore {
paginateData()
}
}
}
// Paginates data
func paginateData() {
fetchingMore = true
var query: Query!
if rides.isEmpty {
query = db.collection("rides").order(by: "price").limit(to: 6)
print("First 6 rides loaded")
} else {
query = db.collection("rides").order(by: "price").start(afterDocument: lastDocumentSnapshot).limit(to: 4)
print("Next 4 rides loaded")
}
query.getDocuments { (snapshot, err) in
if let err = err {
print("\(err.localizedDescription)")
} else if snapshot!.isEmpty {
self.fetchingMore = false
return
} else {
let newRides = snapshot!.documents.compactMap({Ride(dictionary: $0.data())})
self.rides.append(contentsOf: newRides)
//
DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: {
self.tableView.reloadData()
self.fetchingMore = false
})
self.lastDocumentSnapshot = snapshot!.documents.last
}
}
}

Answer 2

A little late in the game, but I would like to share how I do it, using the query.start(afterDocument:) method.
class PostsController: UITableViewController {
let db = Firestore.firestore()
var query: Query!
var documents = [QueryDocumentSnapshot]()
var postArray = [Post]()
override func viewDidLoad() {
super.viewDidLoad()
query = db.collection("myCollection")
.order(by: "post", descending: false)
.limit(to: 15)
getData()
}
func getData() {
query.getDocuments() { (querySnapshot, err) in
if let err = err {
print("Error getting documents: \(err)")
} else {
querySnapshot!.documents.forEach({ (document) in
let data = document.data() as [String: AnyObject]
//Setup your data model
let postItem = Post(post: post, id: id)
self.postArray += [postItem]
self.documents += [document]
})
self.tableView.reloadData()
}
}
}
func paginate() {
//This line is the main pagination code.
//Firestore allows you to fetch document from the last queryDocument
query = query.start(afterDocument: documents.last!)
getData()
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return postArray.count
}
override func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
// Trigger pagination when scrolled to last cell
// Feel free to adjust when you want pagination to be triggered
if (indexPath.row == postArray.count - 1) {
paginate()
}
}
}
Result like so:
Here is a reference.

Answer 3

My solution was similar to #yambo, however, I tried to avoid making extra calls to the database. After the first call to the database, I get back 10 objects and when it is time to load the new page I kept a reference of how many objects and I checked if the count + 9 is in the range of my new count.
#objc func LoadMore() {
let oldCount = self.uploads.count
guard shouldLoadMore else { return }
self.db.getNextPage { (result) in
switch result {
case .failure(let err):
print(err)
case .success(let newPosts):
self.uploads.insert(contentsOf: newPosts, at: self.uploads.count)
if oldCount...oldCount+9 ~= self.uploads.count {
self.shouldLoadMore = false
}
DispatchQueue.main.async {
self.uploadsView.collectionView.reloadData()
}
}
}
}

Answer 4

Simple, Fast and easy way is...
class FeedViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, FeedCellDelegate {
private var quotes = [Quote]() {
didSet{ tbl_Feed.reloadData() }
}
var quote: Quote?
var fetchCount = 10
#IBOutlet weak var tbl_Feed: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
fetchPost()
}
// MARK: - API
func fetchPost() {
reference(.Quotes).limit(to: getResultCount).getDocuments { (snapshot, error) in
guard let documents = snapshot?.documents else { return }
documents.forEach { (doc) in
let quotes = documents.map {(Quote(dictionary: $0.data()))}
self.quotes = quotes
}
}
}
func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
let currentOffset = scrollView.contentOffset.y
let maxxOffset = scrollView.contentSize.height - scrollView.frame.size.height
if maxxOffset - currentOffset <= 300 { // Your cell size 300 is example
fetchCount += 5
fetchPost()
print("DEBUG: Fetching new Data")
}
}
}