使用 PHAsset 获取用户照片库时如何分页

Posted 2023-03-08

【中文标题】使用 PHAsset 获取用户照片库时如何分页

【英文标题】：How To Paginate when using PHAsset to Fetch User Photo library

【发布时间】：2019-02-06 18:39:53

【问题描述】：

我问的问题和here一样 我不明白如何实施解决方案。 我已经尝试了以下

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()
                    

            )
        )
    

在 cellForItemAt 中，我尝试将索引加倍，以便加载下一个 10。我得到的结果是前 10 个帖子的无休止重复。 有人可以展示使用它的正确方法吗？

【参考方案1】：

我试着做你想做的事。我无法将它封装在一个函数中，因为它需要一些公共变量，所以这里是一个 UIViewController 的代码，它有一个 UICollectionView，它按 10 页加载图像，当滚动到最后一个单元格时，它会加载下一个 10 个图像等等。

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)


    

【讨论】：

只有我在获取照片功能中得到这个“UIView.frame 只能从主线程使用”

【参考方案2】：

细化和问题已解决，现在下面的代码工作正常

导入照片 导入照片UI

类 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)