Having troubles with pagination on swift collectionView - swift

Question

My goal is load more info when the user reaches the end of my collectionViewPokemon, but the getPokes func I'm using to achieve this is being called X amount of times, corresponding to the while statement I implemented to get the info from other endpoints. That's far from the behavior I expected.
This is how my code looks:
Service class
class Service {
let baseUrl = "https://pokeapi.co/api/v2/pokemon"
let limit = 20
var offset = 0
var isPaginating = false
func getPokes(pagination: Bool = false,
handler: #escaping ([Pokemon]) -> Void) {
let topCalls = (limit*5)-limit
let originalPokes = [Pokemon]()
let morePokemons = [Pokemon]()
var endpoint = "\(baseUrl)/?limit=\(limit)&offset=\(offset)"
if pagination {
while offset < topCalls {
isPaginating = true
offset += limit
endpoint = "\(baseUrl)/?limit=\(limit)&offset=\(offset)"
self.mainApiCall(mainList: morePokemons, endpoint: endpoint) { (result) in
switch result {
case .success(let pokemons):
handler(pokemons)
if pagination {
self.isPaginating = true
}
case .failure(let error):
print(error)
}
}
}
} else {
self.mainApiCall(mainList: originalPokes, endpoint: endpoint) { (result) in
switch result {
case .success(let pokemons):
handler(pokemons)
case .failure(let error):
print(error)
}
}
}
}
ViewController class (the properties)
class ViewController: UIViewController,
UICollectionViewDelegateFlowLayout,
UICollectionViewDelegate,
UICollectionViewDataSource,
UIScrollViewDelegate {
private let service = Service()
private var pagingChecker = false
var generalList = [Pokemon]()
var pokemons = [Pokemon]()
var morePokemons = [Pokemon]()
. . .
}
viewDidLoad method (this is ok so far)
override func viewDidLoad() {
super.viewDidLoad()
setViews()
service.getPokes(pagination: false) { [self] (pokes) in
pokemons = pokes
generalList += pokemons
DispatchQueue.main.async {
collectionViewPokemon?.reloadData()
}
}
}
scrollViewDidScroll method (here's the error)
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let position = scrollView.contentOffset.y
if position > ((collectionViewPokemon!.contentSize.height) - 200 - scrollView.frame.size.height) {
guard !service.isPaginating else { return }
if !pagingChecker {
service.getPokes(pagination: true) { [self] (morePokes) in
morePokemons = morePokes
generalList += morePokemons
DispatchQueue.main.async {
collectionViewPokemon?.reloadData()
}
}
} else {
pagingChecker = true
print("Done paging.")
}
}
}
The thing is I wanna fetch just one array of pokemons at a time, but instead I'm making all the endpoint calls at the same time, and also appending them to my generalList array, who owns my collectionView datasource and all that stuff.
PD: Idk if it'll help, but here's a screenshot of my console. The first msg is ok, but it should print the others only when the user reaches the end of the CollectionView, and well, that's not happening (instead, they're all coming back at the same time!)
I can't figure out how to get this done. I would really appreciate any advice or correction, thanks.

Answer 1

I figured out what was happening. I was using a while statement to repeat my Api call as long as it satisfy it's condition (limit<topCalls).
So, I worked out some ways to not using that while statement, and ended up using a function to construct every URL, and then, set up a shouldPage parameter that checked if that apiCall needed to be done or not.
This is how my code ended up:
let baseUrl = "https://pokeapi.co/api/v2/pokemon"
let limit = 20
var offset = 0
func getPokes(pageNumber: Int = 1,
shouldPage: Bool = true,
handler: #escaping ([Pokemon]) -> Void) {
let originalPokes = [Pokemon]()
let morePokemons = [Pokemon]()
let endpoint = buildEndpoint(shouldPage: shouldPage)
if shouldPage {
mainApiCall(mainList: morePokemons, endpoint: endpoint) { (result) in
switch result {
case .success(let pokemons):
handler(pokemons)
case .failure(let error):
print(error)
}
}
} else {
mainApiCall(mainList: originalPokes, endpoint: endpoint) { (result) in
switch result {
case .success(let pokemons):
handler(pokemons)
case .failure(let error):
print(error)
}
}
}
}
private func buildEndpoint(shouldPage: Bool = false) -> String {
var endpoint = "\(baseUrl)/?limit=\(limit)&offset=\(offset)"
if shouldPage {
offset += limit
endpoint = "\(baseUrl)/?limit=\(limit)&offset=\(offset)"
}
return endpoint
}
That's on my Service class. So, in my CollectionView Datasource, I call getPokes(shouldPage: false) on cellForItemAt, and in willDisplay cell I say shouldPage is true. That fixed the problem.