UICollection 视图的无限滚动

Question

I'm trying to have unlimited scroll in my app where i'm calling the data from an API, and at least it works to some extent, but when i scroll in the collection view, it starts populating below and it cuts of the ones on top so i can't scroll back up to them, then after populating it just skips and goes out of range, here's some code please help.

var fetchMore = false
var pageNumber = 0

var productPageString: String {
    if pageNumber == 0 {
        return "pageNumber=0&"
    } else {
        return "pageNumber=\(pageNumber)&"
    }
}

func fetchProducts() {
    fetchMore = false
    let validatedTextString = UserDefaults.standard.object(forKey: "productsSearchValue")
    let searchText = validatedTextString!
    let urlString = APIConstants.baseurl + APIConstants.products + "?searchString=\(searchText)&\(productPageString)itemsPerPage=20"
    guard let url = URL(string: urlString) else { return }
    URLSession.shared.dataTask(with: url) { (data, response, error) in
        if error != nil {
            print(error!)
            return
        }
        do {
            let jsonData = try JSONDecoder().decode(ProductSearch.self, from: data!)

            self.productSearchResults = [Products]()

            for dictionary in jsonData.data {
                let product = Products(productId: dictionary.productId, categoryId: dictionary.categoryId, storeId: dictionary.storeId, name: dictionary.name, description: dictionary.description, imageUrl: dictionary.imageUrl, price: dictionary.price)
                self.productSearchResults?.append(product)
                self.fetchMore = true
            }

        } catch let jsonError {
            print(jsonError)
        }
        }.resume()
}

override func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let offsetY = scrollView.contentOffset.y
    let contentHeight = scrollView.contentSize.height

    if offsetY > contentHeight - scrollView.frame.height {
        if fetchMore {
            fetchProducts()
            pageNumber += 1
        }
    }
}

It initially shows the 20 items per page, but as the page number increases, it keeps populating with the other content in that particular page, but i can only still view 20 items per page. i want to be able to scroll back up to the previous ones and also, why does it end up taking me to the end automatically? Thanks

Answer 1

You need to reload

 for dictionary in jsonData.data {
    let product = Products(productId: dictionary.productId, categoryId: dictionary.categoryId, storeId: dictionary.storeId, name: dictionary.name, description: dictionary.description, imageUrl: dictionary.imageUrl, price: dictionary.price)
    self.productSearchResults?.append(product)
 }

 self.fetchMore = true

 DispatchQueue.main.async {
   self.collectionView.reloadData()
 }

Answer 2

It works now, all i had to do was remove the line

self.productSearchResults = [Products]()

it wasn't necessary