问题
I am asking the same question as here I do not understand how to implement to solution. I have tried the following
fileprivate func fetchPhotos(indexSet: IndexSet) {
let allPhotos = PHAsset.fetchAssets(with: .image, options: assetsFetchOptions())
DispatchQueue.global(qos: .background).async {
allPhotos.enumerateObjects(at: indexSet, options: NSEnumerationOptions.concurrent, using: { (asset, count, stop) in
let imageManager = PHImageManager.default()
let targetSize = CGSize(width: 200, height: 200)
let options = PHImageRequestOptions()
options.isSynchronous = true
imageManager.requestImage(for: asset, targetSize: targetSize, contentMode: .aspectFit, options: options, resultHandler: { (image, info) in
if let image = image {
self.images.append(image)
self.assets.append(asset)
if self.selectedImage == nil {
self.selectedImage = image
}
}
DispatchQueue.main.async {
self.collectionView.reloadData()
self.hud.dismiss()
}
})
})
}
}
In cellForItemAt I tried doubling the indexes so the next 10 would load. The result i got was a never ending repetition of the first 10 posts. Can someone please show the proper way to use this.
回答1:
I tried to do what you want. I couldn't encapsulate it inside one function, coz it requires a few public variables, so here is the code for a UIViewController that has a UICollectionView which loads images by a page of 10 and when scrolled to the last cell it loads next 10 images and so on.
import UIKit
import Photos
import PhotosUI
class ImagesViewController: UIViewController ,UICollectionViewDataSource,UICollectionViewDelegate,UICollectionViewDelegateFlowLayout{
var assets = [PHAsset]()
var images = [UIImage]()
let page = 10
var beginIndex = 0
var endIndex = 9
var allPhotos : PHFetchResult<PHAsset>?
var loading = false
var hasNextPage = false
@IBOutlet weak var collectionView : UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
let options = PHFetchOptions()
options.includeHiddenAssets = true
allPhotos = PHAsset.fetchAssets(with: .image, options: options)
getImages()
}
func getImages(){
endIndex = beginIndex + (page - 1)
if endIndex > allPhotos!.count {
endIndex = allPhotos!.count - 1
}
let arr = Array(beginIndex...endIndex)
let indexSet = IndexSet(arr)
fetchPhotos(indexSet: indexSet)
}
fileprivate func fetchPhotos(indexSet: IndexSet) {
if allPhotos!.count == self.images.count {
self.hasNextPage = false
self.loading = false
return
}
self.loading = true
DispatchQueue.global(qos: .background).async { [weak self] in
self?.allPhotos?.enumerateObjects(at: indexSet, options: NSEnumerationOptions.concurrent, using: { (asset, count, stop) in
guard let weakSelf = self else {
return
}
let imageManager = PHImageManager.default()
let targetSize = CGSize(width: weakSelf.view.frame.size.height - 20, height: 250)
let options = PHImageRequestOptions()
options.isSynchronous = true
imageManager.requestImage(for: asset, targetSize: targetSize, contentMode: .aspectFit, options: options, resultHandler: { (image, info) in
if let image = image {
weakSelf.images.append(image)
weakSelf.assets.append(asset)
}
})
if weakSelf.images.count - 1 == indexSet.last! {
print("last element")
weakSelf.loading = false
weakSelf.hasNextPage = weakSelf.images.count != weakSelf.allPhotos!.count
weakSelf.beginIndex = weakSelf.images.count
DispatchQueue.main.async {
weakSelf.collectionView.reloadData()
}
}
})
}
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return images.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
let imgView = cell.viewWithTag(1) as! UIImageView
imgView.image = self.images[indexPath.row]
if self.hasNextPage && !loading && indexPath.row == self.images.count - 1 {
getImages()
}
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width:collectionView.frame.size.width - 20,height: 250)
}
}
回答2:
Refinement and issues Resolved , Now below code Working fine
import Photos import PhotosUI
class PhotoGalleryPaginationViewController: UIViewController,UICollectionViewDataSource,UICollectionViewDelegate {
var assets = [PHAsset]()
var images = [UIImage]()
let page = 10
var beginIndex = 0
var endIndex = 9
var allPhotos : PHFetchResult<PHAsset>?
var loading = false
var hasNextPage = false
@IBOutlet weak var collectionView : UICollectionView!
// MARK :- LIFE CYCLE
override func viewDidLoad() {
super.viewDidLoad()
// Cell Register
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "cell")
// Fetch Gallery
let options = PHFetchOptions()
options.includeHiddenAssets = true
allPhotos = PHAsset.fetchAssets(with: .image, options: options)
getImages()
// Do any additional setup after loading the view.
}
// MARK :- Methods
func getImages(){
endIndex = beginIndex + (page - 1)
if endIndex > allPhotos!.count {
endIndex = allPhotos!.count - 1
}
if endIndex > beginIndex {
let arr = Array(beginIndex...endIndex)
let indexSet = IndexSet(arr)
fetchPhotos(indexSet: indexSet)
}
}
fileprivate func fetchPhotos(indexSet: IndexSet) {
if allPhotos!.count == self.images.count {
self.hasNextPage = false
self.loading = false
return
}
self.loading = true
let targetSize = CGSize(width: 200, height: 200)
DispatchQueue.global(qos: .background).async { [weak self] in
self?.allPhotos?.enumerateObjects(at: indexSet, options: NSEnumerationOptions.concurrent, using: { (asset, count, stop) in
guard let weakSelf = self else {
return
}
let imageManager = PHImageManager.default()
let options = PHImageRequestOptions()
options.isSynchronous = true
imageManager.requestImage(for: asset, targetSize: targetSize, contentMode: .aspectFit, options: options, resultHandler: { (image, info) in
if let image = image {
weakSelf.images.append(image)
weakSelf.assets.append(asset)
}
})
if weakSelf.images.count - 1 == indexSet.last! {
print("last element")
weakSelf.loading = false
weakSelf.hasNextPage = weakSelf.images.count != weakSelf.allPhotos!.count
weakSelf.beginIndex = weakSelf.images.count
DispatchQueue.main.async {
weakSelf.collectionView.reloadData()
}
}
})
}
}
// MARK :- CollectionView DataSource and Delegate
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("image Count = \(images.count)")
return images.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
let imgView = UIImageView()
imgView.frame = CGRect(x: 0, y: 0, width: 150, height: 150)
imgView.image = self.images[indexPath.row]
cell.contentView.addSubview(imgView)
cell.clipsToBounds = true
// Fetch new Images
if self.hasNextPage && !loading && indexPath.row == self.images.count - 1 {
getImages()
}
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width:collectionView.frame.width/2,height: 150)
}
}
来源：https://stackoverflow.com/questions/54560446/how-to-paginate-when-using-phasset-to-fetch-user-photo-library