ios - How to load more object in UICollectionView - ios

Question

I have a collection view and data to load. My goal is when the collection view loaded it's load only first 5 items. And when I scroll to bottom of collection view it's load more 5 items and again until load all the data.
// The data to load (It already have 20 item loaded from server)
static var productInfo: [ProductInfo] = []
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: MainProductCell.reuseIdentifier, for: indexPath) as? MainProductCell else {
fatalError("Expected `\(MainProductCell.self)` type for reuseIdentifier \(MainProductCell.reuseIdentifier). Check the configuration in Main.storyboard.")
}
// Set data for collection cell
cell.modelId = String(ProductCollectionViewController.productInfo[indexPath.row].productId)
cell.modelName = String(ProductCollectionViewController.productInfo[indexPath.row].name)
cell.modelPrice = String(ProductCollectionViewController.productInfo[indexPath.row].price)
cell.modelImage = ProductCollectionViewController.productInfo[indexPath.row].image
cell.objectImageView.downloadedFrom(link: ProductCollectionViewController.productInfo[indexPath.row].image, contentMode: UIViewContentMode.scaleAspectFit)
cell.modelLink = String(ProductCollectionViewController.productInfo[indexPath.row].remoteStorage)
}
return cell
}
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
let lastItem = ProductCollectionViewController.productInfo.count - 1
if indexPath.row == lastItem {
loadMore()
}
}
func loadMore() {
print("load more...")
//How to handle load more here?
}
How to handle the loadMore() function? Thank you.

Answer 1

Till that it's going well plus
if indexPath.row == lastItem && !loading {
loading = true
loadMore()
}

Answer 2

Using itemAtIndexIndexPath to determine the last cell is not the best way, you should check when the scrollView is going to scroll to bottom.
var isScrolledToBottomWithBuffer: Bool {
let buffer = tableView.bounds.height - tableView.contentInset.top - tableView.contentInset.bottom
let maxVisibleY = tableView.contentOffset.y + self.tableView.bounds.size.height
let actualMaxY = tableView.contentSize.height + tableView.contentInset.bottom
return maxVisibleY + buffer >= actualMaxY
}
override func scrollViewDidScroll(_ scrollView: UIScrollView) {
if( scrollView.contentSize.height == 0 ) {
return;
}
if isScrolledToBottomWithBuffer {
self.loadMore()
}
}

Answer 3

Improving upon #duytph answer
var isAllowedToFetchNewDataFromBottom = false
...
var products: [Products] = []
...
collectionView.delegate = self
...
extension AuthorProductsListViewController: UICollectionViewDelegate {
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
if scrollView.contentSize.height == 0 {
return
}
if isScrolledToBottomWithBuffer, isAllowedToFetchNewDataFromBottom {
fetchNewData() {
self.isAllowedToFetchNewDataFromBottom = false
}
}
}
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
lastItemCount = pendingProducts.count
if indexPath.row == lastItemCount - 1 {
isAllowedToFetchNewDataFromBottom = true
}
}
var isScrolledToBottomWithBuffer: Bool {
let buffer = collectionView.bounds.height - collectionView.contentInset.top - collectionView.contentInset.bottom
let maxVisibleY = collectionView.contentOffset.y + self.collectionView.bounds.size.height
let actualMaxY = collectionView.contentSize.height + collectionView.contentInset.bottom
return maxVisibleY + buffer >= actualMaxY
}
}