我在滚动时尝试在集合视图中触发某个函数。基本上我试图实现分页，这样当它滚动到底部时，会加载更多的项目。
override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
if indexPath.item >= allEvents.count - 1 {
// print("paginating for post")
paginationHelper.paginate(completion: { [unowned self] (events) in
self.allEvents.append(contentsOf: events)
DispatchQueue.main.async {
self.collectionView?.reloadData()
}
})
}else{
print("Not paginating")
}
}
这是整个功能
import Foundation
import UIKit
import Alamofire
import AlamofireNetworkActivityIndicator
import SwiftLocation
import CoreLocation
import AMScrollingNavbar
class HomeFeedController: UICollectionViewController, UICollectionViewDelegateFlowLayout,UIGestureRecognizerDelegate {
// let dropDownLauncher = DropDownLauncher()
var isFinishedPaging = false
let detailView = EventDetailViewController()
let refreshControl = UIRefreshControl()
var emptyLabel: UILabel?
var allEvents = [Event]()
//will containt array of event keys
var eventKeys = [String]()
let customCellIdentifier = "customCellIdentifier"
var grideLayout = GridLayout(numberOfColumns: 2)
lazy var dropDownLauncer : DropDownLauncher = {
let launcer = DropDownLauncher()
launcer.homeFeed = self
return launcer
}()
let paginationHelper = PaginationHelper<Event>(serviceMethod: PostService.showEvent)
override func viewDidLoad() {
super.viewDidLoad()
collectionView?.backgroundColor = UIColor.white
collectionView?.collectionViewLayout = grideLayout
collectionView?.reloadData()
self.collectionView?.contentInset = UIEdgeInsetsMake(15, 0, 0, 0)
navigationItem.title = "Home"
collectionView?.register(CustomCell.self, forCellWithReuseIdentifier: customCellIdentifier)
// self.navigationItem.hidesBackButton = true
let backButton = UIBarButtonItem(image: UIImage(named: "menu"), style: .plain, target: self, action: #selector(handleDropDownMenu))
self.navigationItem.leftBarButtonItem = backButton
// PostService.showEvent(location: User.current.location!) { (event) in
// self.allEvents = event
// print(self.allEvents)
//
// DispatchQueue.main.async {
// self.collectionView?.reloadData()
// }
// }
configureCollectionView()
reloadHomeFeed()
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
if let navigationController = self.navigationController as? ScrollingNavigationController {
navigationController.followScrollView(self.collectionView!, delay: 50.0)
}
}
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
if let navigationController = navigationController as? ScrollingNavigationController {
navigationController.stopFollowingScrollView()
}
}
override func scrollViewShouldScrollToTop(_ scrollView: UIScrollView) -> Bool {
if let navigationController = navigationController as? ScrollingNavigationController {
navigationController.showNavbar(animated: true)
}
return true
}
func handleDropDownMenu(){
dropDownLauncer.showDropDown()
}
//will query by selected category
func categoryFetch(dropDown: DropDown){
navigationItem.title = dropDown.name
paginationHelper.category = dropDown.name
configureCollectionView()
reloadHomeFeed()
}
func reloadHomeFeed() {
self.paginationHelper.reloadData(completion: { [unowned self] (events) in
self.allEvents = events
if self.refreshControl.isRefreshing {
self.refreshControl.endRefreshing()
}
DispatchQueue.main.async {
self.collectionView?.reloadData()
}
})
}
func configureCollectionView() {
// add pull to refresh
refreshControl.addTarget(self, action: #selector(reloadHomeFeed), for: .valueChanged)
collectionView?.addSubview(refreshControl)
}
// need to tell it how many cells to have
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return allEvents.count
}
// need to tell the collection view controller what type of cell we want to return
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let customCell = collectionView.dequeueReusableCell(withReuseIdentifier: customCellIdentifier, for: indexPath) as! CustomCell
let imageURL = URL(string: allEvents[indexPath.item].currentEventImage)
print(imageURL ?? "")
customCell.sampleImage.af_setImage(withURL: imageURL!)
return customCell
}
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
//let selectedEvent = self.imageArray[indexPath.row]
//let eventDetailVC
if let cell = collectionView.cellForItem(at: indexPath){
// print("Look here for event name")
// print(detailView.eventName)
detailView.eventKey = allEvents[indexPath.row].key!
detailView.eventPromo = allEvents[indexPath.row].currentEventPromo!
detailView.currentEvent = allEvents[indexPath.row]
present(detailView, animated: true, completion: nil)
//self.navigationController?.pushViewController(detailView, animated: true)
}
print("Cell \(indexPath.row) selected")
}
override func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
if indexPath.item >= allEvents.count - 1 {
// print("paginating for post")
paginationHelper.paginate(completion: { [unowned self] (events) in
self.allEvents.append(contentsOf: events)
DispatchQueue.main.async {
self.collectionView?.reloadData()
}
})
}else{
print("Not paginating")
}
}
func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
return true
}
//will make surepictures keep same orientation even if you flip screen
// will most likely lock into portrait mode but still good to have
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
grideLayout.invalidateLayout()
}
//Will allow the first two cells that are displayed to be of varying widths
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
if indexPath.item == 0 || indexPath.item == 1 {
return CGSize(width: view.frame.width, height: grideLayout.itemSize.height)
}else{
return grideLayout.itemSize
}
}
func showLeftView(sender: AnyObject?){
print("Button Pressed")
// sideMenuController?.leftViewController = LeftViewController()
//sideMenuController?.showLeftView(animated: true, completionHandler: nil)
}
}
//responsible for populating each cell with content
class CustomCell: UICollectionViewCell {
override init(frame: CGRect) {
super.init(frame: frame)
setupViews()
}
let sampleImage: UIImageView = {
let firstImage = UIImageView()
firstImage.clipsToBounds = true
firstImage.translatesAutoresizingMaskIntoConstraints = false
firstImage.contentMode = .scaleToFill
firstImage.layer.masksToBounds = true
return firstImage
}()
let nameLabel: UILabel = {
let name = UILabel()
name.text = "Custom Text"
name.translatesAutoresizingMaskIntoConstraints = false
return name
}()
func setupViews() {
addSubview(sampleImage)
backgroundColor = UIColor.white
//addSubview(nameLabel)
addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0": sampleImage]))
addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[v0]|", options: NSLayoutFormatOptions(), metrics: nil, views: ["v0": sampleImage]))
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
// responsible for creating the grid layout that you see in the home view feed
class GridLayout: UICollectionViewFlowLayout {
var numberOfColumns:Int = 2
init(numberOfColumns: Int) {
super.init()
// controlls spacing inbetween them as well as spacing below them to next item
self.numberOfColumns = numberOfColumns
self.minimumInteritemSpacing = 3
self.minimumLineSpacing = 5
}
// just needs to be here because swift tells us to
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override var itemSize: CGSize{
get{
if collectionView != nil {
let collectionVieweWidth = collectionView?.frame.width
let itemWidth = (collectionVieweWidth!/CGFloat(self.numberOfColumns)) - self.minimumInteritemSpacing
let itemHeight: CGFloat = 200
return CGSize(width: itemWidth, height: itemHeight)
}
return CGSize(width: 100, height: 100)
}set{
super.itemSize = newValue
}
}
}
这是负责触发事件的函数，但它似乎每次都按字面意思转到else语句。任何见解都会有所帮助