Swift - 如何从照片库中获取最近拍摄的 3 张照片？
Swift - how to get last taken 3 photos from photo library?
我需要在 viewDidload 活动中获取并显示照片库中最后拍摄的 3 张照片，无需任何点击。
完成这一步后，当我滚动 ScrollView 时，我应该会得到其他照片 3 x 3。
您知道使用 swift 执行此操作的正确方法吗？谢谢
您可以使用AssetsLibrary框架中的函数提取最新的3张照片。首先，您必须将框架添加到项目中。以下函数检索 3 张最新照片并调用完成块。
import AssetsLibrary
func getLatestPhotos(completion completionBlock : ([UIImage] -> ())) {
let library = ALAssetsLibrary()
var count = 0
var images : [UIImage] = []
var stopped = false
library.enumerateGroupsWithTypes(ALAssetsGroupSavedPhotos, usingBlock: { (group,var stop) -> Void in
group?.setAssetsFilter(ALAssetsFilter.allPhotos())
group?.enumerateAssetsWithOptions(NSEnumerationOptions.Reverse, usingBlock: {
(asset : ALAsset!, index, var stopEnumeration) -> Void in
if (!stopped)
{
if count >= 3
{
stopEnumeration.memory = ObjCBool(true)
stop.memory = ObjCBool(true)
completionBlock(images)
stopped = true
}
else
{
// For just the thumbnails use the following line.
let cgImage = asset.thumbnail().takeUnretainedValue()
// Use the following line for the full image.
let cgImage = asset.defaultRepresentation().fullScreenImage().takeUnretainedValue()
if let image = UIImage(CGImage: cgImage) {
images.append(image)
count += 1
}
}
}
})
},failureBlock : { error in
println(error)
})
}
上面的函数可以这样调用
getLatestPhotos(completion: { images in
println(images)
//Set Images in this block.
})
这是一个使用 Photos 框架的解决方案，适用于 iOS 8+ 设备：
import Photos
class ViewController: UIViewController {
var images:[UIImage] = []
func fetchPhotos () {
// Sort the images by descending creation date and fetch the first 3
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key:"creationDate", ascending: false)]
fetchOptions.fetchLimit = 3
// Fetch the image assets
let fetchResult: PHFetchResult = PHAsset.fetchAssets(with: PHAssetMediaType.image, options: fetchOptions)
// If the fetch result isn't empty,
// proceed with the image request
if fetchResult.count > 0 {
let totalImageCountNeeded = 3 // <-- The number of images to fetch
fetchPhotoAtIndex(0, totalImageCountNeeded, fetchResult)
}
}
// Repeatedly call the following method while incrementing
// the index until all the photos are fetched
func fetchPhotoAtIndex(_ index:Int, _ totalImageCountNeeded: Int, _ fetchResult: PHFetchResult<PHAsset>) {
// Note that if the request is not set to synchronous
// the requestImageForAsset will return both the image
// and thumbnail; by setting synchronous to true it
// will return just the thumbnail
let requestOptions = PHImageRequestOptions()
requestOptions.isSynchronous = true
// Perform the image request
PHImageManager.default().requestImage(for: fetchResult.object(at: index) as PHAsset, targetSize: view.frame.size, contentMode: PHImageContentMode.aspectFill, options: requestOptions, resultHandler: { (image, _) in
if let image = image {
// Add the returned image to your array
self.images += [image]
}
// If you haven't already reached the first
// index of the fetch result and if you haven't
// already stored all of the images you need,
// perform the fetch request again with an
// incremented index
if index + 1 < fetchResult.count && self.images.count < totalImageCountNeeded {
self.fetchPhotoAtIndex(index + 1, totalImageCountNeeded, fetchResult)
} else {
// Else you have completed creating your array
print("Completed array: \(self.images)")
}
})
}
}
这是@Lindsey Scott 的回答，但在 Objective-C 中。我将相机胶卷中的最后 9 张照片放入 collection 视图：
-(void)fetchPhotoFromEndAtIndex:(int)index{
PHImageRequestOptions *options = [[PHImageRequestOptions alloc]init];
options.synchronous = YES;
PHFetchOptions *fetchOptions = [[PHFetchOptions alloc]init];
fetchOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:YES]];
PHFetchResult *photos = [PHAsset fetchAssetsWithMediaType:PHAssetMediaTypeImage options:fetchOptions];
if (photos) {
[[PHImageManager defaultManager] requestImageForAsset:[photos objectAtIndex:photos.count -1 -index] targetSize:CGSizeMake(self.collectionView.frame.size.width/3, self.collectionView.frame.size.height/3) contentMode:PHImageContentModeAspectFill options:options resultHandler:^(UIImage *result, NSDictionary *info) {
[self.imagesArray addObject:result];
if (index + 1 < photos.count && self.imagesArray.count < 9) {
[self fetchPhotoFromEndAtIndex:index + 1];
}
}];
}
[self.collectionView reloadData];
}
详情
- Xcode 10.2 (10E125), Swift 5
解决方案特点
- 异步工作并且thread/queue安全
- 获取相册（+所有照片相册）
- 针对快速滚动进行了优化
- 获取定义大小的图像
Info.plist
Add to Info.plist
<key>NSPhotoLibraryUsageDescription</key>
<string>{bla-bla-bla}</string>
解决方案
AtomicArray here:
import UIKit
import Photos
enum PhotoAlbumViewModel {
case regular(id: Int, title: String, count: Int, image: UIImage, isSelected: Bool)
case allPhotos(id: Int, title: String, count: Int, image: UIImage, isSelected: Bool)
var id: Int { switch self { case .regular(let params), .allPhotos(let params): return params.id } }
var count: Int { switch self { case .regular(let params), .allPhotos(let params): return params.count } }
var title: String { switch self { case .regular(let params), .allPhotos(let params): return params.title } }
}
class PhotoService {
internal lazy var imageManager = PHCachingImageManager()
private lazy var queue = DispatchQueue(label: "PhotoService_queue",
qos: .default, attributes: .concurrent,
autoreleaseFrequency: .workItem, target: nil)
private lazy var getImagesQueue = DispatchQueue(label: "PhotoService_getImagesQueue",
qos: .userInteractive, attributes: [],
autoreleaseFrequency: .inherit, target: nil)
private lazy var thumbnailSize = CGSize(width: 200, height: 200)
private lazy var imageAlbumsIds = AtomicArray<Int>()
private let getImageSemaphore = DispatchSemaphore(value: 12)
typealias AlbumData = (fetchResult: PHFetchResult<PHAsset>, assetCollection: PHAssetCollection?)
private let _cachedAlbumsDataSemaphore = DispatchSemaphore(value: 1)
private lazy var _cachedAlbumsData = [Int: AlbumData]()
deinit {
print("____ PhotoServiceImpl deinited")
imageManager.stopCachingImagesForAllAssets()
}
}
// albums
extension PhotoService {
private func getAlbumData(id: Int, completion: ((AlbumData?) -> Void)?) {
_ = _cachedAlbumsDataSemaphore.wait(timeout: .now() + .seconds(3))
if let cachedAlbum = _cachedAlbumsData[id] {
completion?(cachedAlbum)
_cachedAlbumsDataSemaphore.signal()
return
} else {
_cachedAlbumsDataSemaphore.signal()
}
var result: AlbumData? = nil
switch id {
case 0:
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let allPhotos = PHAsset.fetchAssets(with: .image, options: fetchOptions)
result = (allPhotos, nil)
default:
let collections = getAllAlbumsAssetCollections()
let id = id - 1
if id < collections.count {
_fetchAssets(in: collections[id]) { fetchResult in
result = (fetchResult, collections[id])
}
}
}
guard let _result = result else { completion?(nil); return }
_ = _cachedAlbumsDataSemaphore.wait(timeout: .now() + .seconds(3))
_cachedAlbumsData[id] = _result
_cachedAlbumsDataSemaphore.signal()
completion?(_result)
}
private func getAllAlbumsAssetCollections() -> PHFetchResult<PHAssetCollection> {
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "endDate", ascending: true)]
fetchOptions.predicate = NSPredicate(format: "estimatedAssetCount > 0")
return PHAssetCollection.fetchAssetCollections(with: .album, subtype: .any, options: fetchOptions)
}
func getAllAlbums(completion: (([PhotoAlbumViewModel])->Void)?) {
queue.async { [weak self] in
guard let self = self else { return }
var viewModels = AtomicArray<PhotoAlbumViewModel>()
var allPhotosAlbumViewModel: PhotoAlbumViewModel?
let dispatchGroup = DispatchGroup()
dispatchGroup.enter()
self.getAlbumData(id: 0) { data in
guard let data = data, let asset = data.fetchResult.lastObject else { dispatchGroup.leave(); return }
self._fetchImage(from: asset, userInfo: nil, targetSize: self.thumbnailSize,
deliveryMode: .fastFormat, resizeMode: .fast) { [weak self] (image, _) in
guard let self = self, let image = image else { dispatchGroup.leave(); return }
allPhotosAlbumViewModel = .allPhotos(id: 0, title: "All Photos",
count: data.fetchResult.count,
image: image, isSelected: false)
self.imageAlbumsIds.append(0)
dispatchGroup.leave()
}
}
let numberOfAlbums = self.getAllAlbumsAssetCollections().count + 1
for id in 1 ..< numberOfAlbums {
dispatchGroup.enter()
self.getAlbumData(id: id) { [weak self] data in
guard let self = self else { return }
guard let assetCollection = data?.assetCollection else { dispatchGroup.leave(); return }
self.imageAlbumsIds.append(id)
self.getAlbumViewModel(id: id, collection: assetCollection) { [weak self] model in
guard let self = self else { return }
defer { dispatchGroup.leave() }
guard let model = model else { return }
viewModels.append(model)
}
}
}
_ = dispatchGroup.wait(timeout: .now() + .seconds(3))
var _viewModels = [PhotoAlbumViewModel]()
if let allPhotosAlbumViewModel = allPhotosAlbumViewModel {
_viewModels.append(allPhotosAlbumViewModel)
}
_viewModels += viewModels.get()
DispatchQueue.main.async { completion?(_viewModels) }
}
}
private func getAlbumViewModel(id: Int, collection: PHAssetCollection, completion: ((PhotoAlbumViewModel?) -> Void)?) {
_fetchAssets(in: collection) { [weak self] fetchResult in
guard let self = self, let asset = fetchResult.lastObject else { completion?(nil); return }
self._fetchImage(from: asset, userInfo: nil, targetSize: self.thumbnailSize,
deliveryMode: .fastFormat, resizeMode: .fast) { (image, nil) in
guard let image = image else { completion?(nil); return }
completion?(.regular(id: id,
title: collection.localizedTitle ?? "",
count: collection.estimatedAssetCount,
image: image, isSelected: false))
}
}
}
}
// fetch
extension PhotoService {
fileprivate func _fetchImage(from photoAsset: PHAsset,
userInfo: [AnyHashable: Any]? = nil,
targetSize: CGSize, //= PHImageManagerMaximumSize,
deliveryMode: PHImageRequestOptionsDeliveryMode = .fastFormat,
resizeMode: PHImageRequestOptionsResizeMode,
completion: ((_ image: UIImage?, _ userInfo: [AnyHashable: Any]?) -> Void)?) {
// guard authorizationStatus() == .authorized else { completion(nil); return }
let options = PHImageRequestOptions()
options.resizeMode = resizeMode
options.isSynchronous = true
options.deliveryMode = deliveryMode
imageManager.requestImage(for: photoAsset,
targetSize: targetSize,
contentMode: .aspectFill,
options: options) { (image, info) -> Void in
guard let info = info,
let isImageDegraded = info[PHImageResultIsDegradedKey] as? Int,
isImageDegraded == 0 else { completion?(nil, nil); return }
completion?(image, userInfo)
}
}
private func _fetchAssets(in collection: PHAssetCollection, completion: @escaping (PHFetchResult<PHAsset>) -> Void) {
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let assets = PHAsset.fetchAssets(in: collection, options: fetchOptions)
completion(assets)
}
private func fetchImage(from asset: PHAsset,
userInfo: [AnyHashable: Any]?,
targetSize: CGSize,
deliveryMode: PHImageRequestOptionsDeliveryMode,
resizeMode: PHImageRequestOptionsResizeMode,
completion: ((UIImage?, _ userInfo: [AnyHashable: Any]?) -> Void)?) {
queue.async { [weak self] in
self?._fetchImage(from: asset, userInfo: userInfo, targetSize: targetSize,
deliveryMode: deliveryMode, resizeMode: resizeMode) { (image, _) in
DispatchQueue.main.async { completion?(image, userInfo) }
}
}
}
func getImage(albumId: Int, index: Int,
userInfo: [AnyHashable: Any]?,
targetSize: CGSize,
deliveryMode: PHImageRequestOptionsDeliveryMode,
resizeMode: PHImageRequestOptionsResizeMode,
completion: ((_ image: UIImage?, _ userInfo: [AnyHashable: Any]?) -> Void)?) {
getImagesQueue.async { [weak self] in
guard let self = self else { return }
let indexPath = IndexPath(item: index, section: albumId)
self.getAlbumData(id: albumId) { data in
_ = self.getImageSemaphore.wait(timeout: .now() + .seconds(3))
guard let photoAsset = data?.fetchResult.object(at: index) else { self.getImageSemaphore.signal(); return }
self.fetchImage(from: photoAsset,
userInfo: userInfo,
targetSize: targetSize,
deliveryMode: deliveryMode,
resizeMode: resizeMode) { [weak self] (image, userInfo) in
defer { self?.getImageSemaphore.signal() }
completion?(image, userInfo)
}
}
}
}
}
用法
private lazy var photoLibrary = PhotoService()
private var albums = [PhotoAlbumViewModel]()
//....
// Get albums
photoLibrary.getAllAlbums { [weak self] albums in
self?.albums = albums
// reload views
}
// Get photo
photoLibrary.getImage(albumId: albums[0].id,
index: 1, userInfo: nil,
targetSize: CGSize(width: 200, height: 200),
deliveryMode: .fastFormat,
resizeMode: .fast) { [weak self, weak cell] (image, userInfo) in
// reload views
}
完整示例（带有来自 PhotoLibrary 的图像的 collectionView）
ViewController.swift
import UIKit
import Photos
class ViewController: UIViewController {
private weak var collectionView: UICollectionView?
var collectionViewFlowLayout: UICollectionViewFlowLayout? {
return collectionView?.collectionViewLayout as? UICollectionViewFlowLayout
}
private lazy var photoLibrary = PhotoService()
private lazy var numberOfElementsInRow = 4
private lazy var cellIdentifier = "cellIdentifier"
private lazy var supplementaryViewIdentifier = "supplementaryViewIdentifier"
private var albums = [PhotoAlbumViewModel]()
private lazy var cellsTags = [IndexPath: Int]()
private lazy var tagKey = "cellTag"
private lazy var thumbnailImageSize = CGSize(width: 200, height: 200)
override func viewDidLoad() {
let collectionViewFlowLayout = UICollectionViewFlowLayout()
collectionViewFlowLayout.minimumLineSpacing = 5
collectionViewFlowLayout.minimumInteritemSpacing = 5
let _numberOfElementsInRow = CGFloat(numberOfElementsInRow)
let allWidthBetwenCells = _numberOfElementsInRow == 0 ? 0 : collectionViewFlowLayout.minimumInteritemSpacing*(_numberOfElementsInRow-1)
let width = (view.frame.width - allWidthBetwenCells)/_numberOfElementsInRow
collectionViewFlowLayout.itemSize = CGSize(width: width, height: width)
collectionViewFlowLayout.headerReferenceSize = CGSize(width: 0, height: 40)
let collectionView = UICollectionView(frame: .zero, collectionViewLayout: collectionViewFlowLayout)
view.addSubview(collectionView)
collectionView.translatesAutoresizingMaskIntoConstraints = false
collectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
collectionView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
collectionView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true
collectionView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor).isActive = true
collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: cellIdentifier)
collectionView.register(SupplementaryView.self,
forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
withReuseIdentifier: supplementaryViewIdentifier)
collectionView.backgroundColor = .white
self.collectionView = collectionView
collectionView.delegate = self
showAllPhotosButtonTouchedInside()
navigationItem.leftBarButtonItem = UIBarButtonItem(title: "All", style: .done, target: self,
action: #selector(showAllPhotosButtonTouchedInside))
navigationItem.rightBarButtonItem = UIBarButtonItem(title: "last 3", style: .done, target: self,
action: #selector(showLastSeveralPhotosButtonTouchedInside))
}
@objc func showAllPhotosButtonTouchedInside() {
photoLibrary.getAllAlbums { [weak self] albums in
self?.set(albums: albums)
if self?.collectionView?.dataSource == nil {
self?.collectionView?.dataSource = self
} else {
self?.collectionView?.reloadData()
}
}
}
@objc func showLastSeveralPhotosButtonTouchedInside() {
photoLibrary.getAllAlbums { [weak self] albums in
guard let firstAlbum = albums.first else { return }
var album: PhotoAlbumViewModel!
let maxPhotosToDisplay = 3
switch firstAlbum {
case .allPhotos(let id, let title, let count, let image, let isSelected):
let newCount = count > maxPhotosToDisplay ? maxPhotosToDisplay : count
album = .allPhotos(id: id, title: title, count: newCount, image: image, isSelected: isSelected)
case .regular(let id, let title, let count, let image, let isSelected):
let newCount = count > maxPhotosToDisplay ? maxPhotosToDisplay : count
album = .regular(id: id, title: title, count: newCount, image: image, isSelected: isSelected)
}
self?.set(albums: [album])
if self?.collectionView?.dataSource == nil {
self?.collectionView?.dataSource = self
} else {
self?.collectionView?.reloadData()
}
}
}
private func set(albums: [PhotoAlbumViewModel]) {
self.albums = albums
var counter = 0
for (section, album) in albums.enumerated() {
for row in 0..<album.count {
self.cellsTags[IndexPath(row: row, section: section)] = counter
counter += 1
}
}
}
}
extension ViewController: UICollectionViewDataSource {
func numberOfSections(in collectionView: UICollectionView) -> Int { return albums.count }
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return albums[section].count
}
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: supplementaryViewIdentifier, for: indexPath) as! SupplementaryView
header.label?.text = albums[indexPath.section].title
return header
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CollectionViewCell
let tag = cellsTags[indexPath]!
cell.tag = tag
photoLibrary.getImage(albumId: albums[indexPath.section].id,
index: indexPath.item, userInfo: [tagKey: tag],
targetSize: thumbnailImageSize,
deliveryMode: .fastFormat,
resizeMode: .fast) { [weak self, weak cell] (image, userInfo) in
guard let cell = cell, let tagKey = self?.tagKey,
let cellTag = userInfo?[tagKey] as? Int,
cellTag == cell.tag else { return }
cell.imageView?.image = image
}
return cell
}
}
extension ViewController: UICollectionViewDelegate {}
CollectionViewCell.swift
import UIKit
class CollectionViewCell: UICollectionViewCell {
weak var imageView: UIImageView?
override init(frame: CGRect) {
super.init(frame: frame)
clipsToBounds = true
let imageView = UIImageView(frame: .zero)
imageView.contentMode = .scaleAspectFill
addSubview(imageView)
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.topAnchor.constraint(equalTo: topAnchor).isActive = true
imageView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
imageView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
imageView.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
self.imageView = imageView
backgroundColor = UIColor.lightGray.withAlphaComponent(0.3)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func prepareForReuse() {
super.prepareForReuse()
imageView?.image = nil
}
}
SupplementaryView.swift
import UIKit
class SupplementaryView: UICollectionReusableView {
weak var label: UILabel?
override init(frame: CGRect) {
super.init(frame: frame)
backgroundColor = .white
let label = UILabel(frame: frame)
label.textColor = .black
addSubview(label)
self.label = label
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func prepareForReuse() {
super.prepareForReuse()
self.label?.text = nil
}
}
故事板
结果
这是一个优雅的解决方案，效率在 Swift 4.
简而言之，我们请求一次最新的照片资源，然后在需要时将其转换为图像。
首先导入照片库：
import Photos
然后创建一个函数来获取最新拍摄的照片：
func fetchLatestPhotos(forCount count: Int?) -> PHFetchResult<PHAsset> {
// Create fetch options.
let options = PHFetchOptions()
// If count limit is specified.
if let count = count { options.fetchLimit = count }
// Add sortDescriptor so the lastest photos will be returned.
let sortDescriptor = NSSortDescriptor(key: "creationDate", ascending: false)
options.sortDescriptors = [sortDescriptor]
// Fetch the photos.
return PHAsset.fetchAssets(with: .image, options: options)
}
在您的情况下，您可能希望一次获取足够多的照片（例如 50 张），然后将结果存储在视图控制器中的某个位置：
var latestPhotoAssetsFetched: PHFetchResult<PHAsset>? = nil
在viewDidLoad中：
self.latestPhotoAssetsFetched = self.fetchLatestPhotos(forCount: 50)
最终在正确的位置请求图像（例如，集合视图单元格）：
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
/*
...your code to configure the cell...
*/
// Get the asset. If nothing, return the cell.
guard let asset = self.latestPhotoAssetsFetched?[indexPath.item] else {
return cell
}
// Here we bind the asset with the cell.
cell.representedAssetIdentifier = asset.localIdentifier
// Request the image.
PHImageManager.default().requestImage(for: asset,
targetSize: cell.imageView.frame.size,
contentMode: .aspectFill,
options: nil) { (image, _) in
// By the time the image is returned, the cell may has been recycled.
// We update the UI only when it is still on the screen.
if cell.representedAssetIdentifier == asset.localIdentifier {
cell.imageView.image = image
}
}
return cell
}
记得在您的单元格中添加一个 属性：
class PhotoCell: UICollectionViewCell {
var representedAssetIdentifier: String? = nil
}
我需要在 viewDidload 活动中获取并显示照片库中最后拍摄的 3 张照片，无需任何点击。
完成这一步后，当我滚动 ScrollView 时，我应该会得到其他照片 3 x 3。
您知道使用 swift 执行此操作的正确方法吗？谢谢
您可以使用AssetsLibrary框架中的函数提取最新的3张照片。首先，您必须将框架添加到项目中。以下函数检索 3 张最新照片并调用完成块。
import AssetsLibrary
func getLatestPhotos(completion completionBlock : ([UIImage] -> ())) {
let library = ALAssetsLibrary()
var count = 0
var images : [UIImage] = []
var stopped = false
library.enumerateGroupsWithTypes(ALAssetsGroupSavedPhotos, usingBlock: { (group,var stop) -> Void in
group?.setAssetsFilter(ALAssetsFilter.allPhotos())
group?.enumerateAssetsWithOptions(NSEnumerationOptions.Reverse, usingBlock: {
(asset : ALAsset!, index, var stopEnumeration) -> Void in
if (!stopped)
{
if count >= 3
{
stopEnumeration.memory = ObjCBool(true)
stop.memory = ObjCBool(true)
completionBlock(images)
stopped = true
}
else
{
// For just the thumbnails use the following line.
let cgImage = asset.thumbnail().takeUnretainedValue()
// Use the following line for the full image.
let cgImage = asset.defaultRepresentation().fullScreenImage().takeUnretainedValue()
if let image = UIImage(CGImage: cgImage) {
images.append(image)
count += 1
}
}
}
})
},failureBlock : { error in
println(error)
})
}
上面的函数可以这样调用
getLatestPhotos(completion: { images in
println(images)
//Set Images in this block.
})
这是一个使用 Photos 框架的解决方案，适用于 iOS 8+ 设备：
import Photos
class ViewController: UIViewController {
var images:[UIImage] = []
func fetchPhotos () {
// Sort the images by descending creation date and fetch the first 3
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key:"creationDate", ascending: false)]
fetchOptions.fetchLimit = 3
// Fetch the image assets
let fetchResult: PHFetchResult = PHAsset.fetchAssets(with: PHAssetMediaType.image, options: fetchOptions)
// If the fetch result isn't empty,
// proceed with the image request
if fetchResult.count > 0 {
let totalImageCountNeeded = 3 // <-- The number of images to fetch
fetchPhotoAtIndex(0, totalImageCountNeeded, fetchResult)
}
}
// Repeatedly call the following method while incrementing
// the index until all the photos are fetched
func fetchPhotoAtIndex(_ index:Int, _ totalImageCountNeeded: Int, _ fetchResult: PHFetchResult<PHAsset>) {
// Note that if the request is not set to synchronous
// the requestImageForAsset will return both the image
// and thumbnail; by setting synchronous to true it
// will return just the thumbnail
let requestOptions = PHImageRequestOptions()
requestOptions.isSynchronous = true
// Perform the image request
PHImageManager.default().requestImage(for: fetchResult.object(at: index) as PHAsset, targetSize: view.frame.size, contentMode: PHImageContentMode.aspectFill, options: requestOptions, resultHandler: { (image, _) in
if let image = image {
// Add the returned image to your array
self.images += [image]
}
// If you haven't already reached the first
// index of the fetch result and if you haven't
// already stored all of the images you need,
// perform the fetch request again with an
// incremented index
if index + 1 < fetchResult.count && self.images.count < totalImageCountNeeded {
self.fetchPhotoAtIndex(index + 1, totalImageCountNeeded, fetchResult)
} else {
// Else you have completed creating your array
print("Completed array: \(self.images)")
}
})
}
}
这是@Lindsey Scott 的回答，但在 Objective-C 中。我将相机胶卷中的最后 9 张照片放入 collection 视图：
-(void)fetchPhotoFromEndAtIndex:(int)index{
PHImageRequestOptions *options = [[PHImageRequestOptions alloc]init];
options.synchronous = YES;
PHFetchOptions *fetchOptions = [[PHFetchOptions alloc]init];
fetchOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:YES]];
PHFetchResult *photos = [PHAsset fetchAssetsWithMediaType:PHAssetMediaTypeImage options:fetchOptions];
if (photos) {
[[PHImageManager defaultManager] requestImageForAsset:[photos objectAtIndex:photos.count -1 -index] targetSize:CGSizeMake(self.collectionView.frame.size.width/3, self.collectionView.frame.size.height/3) contentMode:PHImageContentModeAspectFill options:options resultHandler:^(UIImage *result, NSDictionary *info) {
[self.imagesArray addObject:result];
if (index + 1 < photos.count && self.imagesArray.count < 9) {
[self fetchPhotoFromEndAtIndex:index + 1];
}
}];
}
[self.collectionView reloadData];
}
详情
- Xcode 10.2 (10E125), Swift 5
解决方案特点
- 异步工作并且thread/queue安全
- 获取相册（+所有照片相册）
- 针对快速滚动进行了优化
- 获取定义大小的图像
Info.plist
Add to Info.plist
<key>NSPhotoLibraryUsageDescription</key>
<string>{bla-bla-bla}</string>
解决方案
AtomicArray here:
import UIKit
import Photos
enum PhotoAlbumViewModel {
case regular(id: Int, title: String, count: Int, image: UIImage, isSelected: Bool)
case allPhotos(id: Int, title: String, count: Int, image: UIImage, isSelected: Bool)
var id: Int { switch self { case .regular(let params), .allPhotos(let params): return params.id } }
var count: Int { switch self { case .regular(let params), .allPhotos(let params): return params.count } }
var title: String { switch self { case .regular(let params), .allPhotos(let params): return params.title } }
}
class PhotoService {
internal lazy var imageManager = PHCachingImageManager()
private lazy var queue = DispatchQueue(label: "PhotoService_queue",
qos: .default, attributes: .concurrent,
autoreleaseFrequency: .workItem, target: nil)
private lazy var getImagesQueue = DispatchQueue(label: "PhotoService_getImagesQueue",
qos: .userInteractive, attributes: [],
autoreleaseFrequency: .inherit, target: nil)
private lazy var thumbnailSize = CGSize(width: 200, height: 200)
private lazy var imageAlbumsIds = AtomicArray<Int>()
private let getImageSemaphore = DispatchSemaphore(value: 12)
typealias AlbumData = (fetchResult: PHFetchResult<PHAsset>, assetCollection: PHAssetCollection?)
private let _cachedAlbumsDataSemaphore = DispatchSemaphore(value: 1)
private lazy var _cachedAlbumsData = [Int: AlbumData]()
deinit {
print("____ PhotoServiceImpl deinited")
imageManager.stopCachingImagesForAllAssets()
}
}
// albums
extension PhotoService {
private func getAlbumData(id: Int, completion: ((AlbumData?) -> Void)?) {
_ = _cachedAlbumsDataSemaphore.wait(timeout: .now() + .seconds(3))
if let cachedAlbum = _cachedAlbumsData[id] {
completion?(cachedAlbum)
_cachedAlbumsDataSemaphore.signal()
return
} else {
_cachedAlbumsDataSemaphore.signal()
}
var result: AlbumData? = nil
switch id {
case 0:
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let allPhotos = PHAsset.fetchAssets(with: .image, options: fetchOptions)
result = (allPhotos, nil)
default:
let collections = getAllAlbumsAssetCollections()
let id = id - 1
if id < collections.count {
_fetchAssets(in: collections[id]) { fetchResult in
result = (fetchResult, collections[id])
}
}
}
guard let _result = result else { completion?(nil); return }
_ = _cachedAlbumsDataSemaphore.wait(timeout: .now() + .seconds(3))
_cachedAlbumsData[id] = _result
_cachedAlbumsDataSemaphore.signal()
completion?(_result)
}
private func getAllAlbumsAssetCollections() -> PHFetchResult<PHAssetCollection> {
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "endDate", ascending: true)]
fetchOptions.predicate = NSPredicate(format: "estimatedAssetCount > 0")
return PHAssetCollection.fetchAssetCollections(with: .album, subtype: .any, options: fetchOptions)
}
func getAllAlbums(completion: (([PhotoAlbumViewModel])->Void)?) {
queue.async { [weak self] in
guard let self = self else { return }
var viewModels = AtomicArray<PhotoAlbumViewModel>()
var allPhotosAlbumViewModel: PhotoAlbumViewModel?
let dispatchGroup = DispatchGroup()
dispatchGroup.enter()
self.getAlbumData(id: 0) { data in
guard let data = data, let asset = data.fetchResult.lastObject else { dispatchGroup.leave(); return }
self._fetchImage(from: asset, userInfo: nil, targetSize: self.thumbnailSize,
deliveryMode: .fastFormat, resizeMode: .fast) { [weak self] (image, _) in
guard let self = self, let image = image else { dispatchGroup.leave(); return }
allPhotosAlbumViewModel = .allPhotos(id: 0, title: "All Photos",
count: data.fetchResult.count,
image: image, isSelected: false)
self.imageAlbumsIds.append(0)
dispatchGroup.leave()
}
}
let numberOfAlbums = self.getAllAlbumsAssetCollections().count + 1
for id in 1 ..< numberOfAlbums {
dispatchGroup.enter()
self.getAlbumData(id: id) { [weak self] data in
guard let self = self else { return }
guard let assetCollection = data?.assetCollection else { dispatchGroup.leave(); return }
self.imageAlbumsIds.append(id)
self.getAlbumViewModel(id: id, collection: assetCollection) { [weak self] model in
guard let self = self else { return }
defer { dispatchGroup.leave() }
guard let model = model else { return }
viewModels.append(model)
}
}
}
_ = dispatchGroup.wait(timeout: .now() + .seconds(3))
var _viewModels = [PhotoAlbumViewModel]()
if let allPhotosAlbumViewModel = allPhotosAlbumViewModel {
_viewModels.append(allPhotosAlbumViewModel)
}
_viewModels += viewModels.get()
DispatchQueue.main.async { completion?(_viewModels) }
}
}
private func getAlbumViewModel(id: Int, collection: PHAssetCollection, completion: ((PhotoAlbumViewModel?) -> Void)?) {
_fetchAssets(in: collection) { [weak self] fetchResult in
guard let self = self, let asset = fetchResult.lastObject else { completion?(nil); return }
self._fetchImage(from: asset, userInfo: nil, targetSize: self.thumbnailSize,
deliveryMode: .fastFormat, resizeMode: .fast) { (image, nil) in
guard let image = image else { completion?(nil); return }
completion?(.regular(id: id,
title: collection.localizedTitle ?? "",
count: collection.estimatedAssetCount,
image: image, isSelected: false))
}
}
}
}
// fetch
extension PhotoService {
fileprivate func _fetchImage(from photoAsset: PHAsset,
userInfo: [AnyHashable: Any]? = nil,
targetSize: CGSize, //= PHImageManagerMaximumSize,
deliveryMode: PHImageRequestOptionsDeliveryMode = .fastFormat,
resizeMode: PHImageRequestOptionsResizeMode,
completion: ((_ image: UIImage?, _ userInfo: [AnyHashable: Any]?) -> Void)?) {
// guard authorizationStatus() == .authorized else { completion(nil); return }
let options = PHImageRequestOptions()
options.resizeMode = resizeMode
options.isSynchronous = true
options.deliveryMode = deliveryMode
imageManager.requestImage(for: photoAsset,
targetSize: targetSize,
contentMode: .aspectFill,
options: options) { (image, info) -> Void in
guard let info = info,
let isImageDegraded = info[PHImageResultIsDegradedKey] as? Int,
isImageDegraded == 0 else { completion?(nil, nil); return }
completion?(image, userInfo)
}
}
private func _fetchAssets(in collection: PHAssetCollection, completion: @escaping (PHFetchResult<PHAsset>) -> Void) {
let fetchOptions = PHFetchOptions()
fetchOptions.sortDescriptors = [NSSortDescriptor(key: "creationDate", ascending: true)]
let assets = PHAsset.fetchAssets(in: collection, options: fetchOptions)
completion(assets)
}
private func fetchImage(from asset: PHAsset,
userInfo: [AnyHashable: Any]?,
targetSize: CGSize,
deliveryMode: PHImageRequestOptionsDeliveryMode,
resizeMode: PHImageRequestOptionsResizeMode,
completion: ((UIImage?, _ userInfo: [AnyHashable: Any]?) -> Void)?) {
queue.async { [weak self] in
self?._fetchImage(from: asset, userInfo: userInfo, targetSize: targetSize,
deliveryMode: deliveryMode, resizeMode: resizeMode) { (image, _) in
DispatchQueue.main.async { completion?(image, userInfo) }
}
}
}
func getImage(albumId: Int, index: Int,
userInfo: [AnyHashable: Any]?,
targetSize: CGSize,
deliveryMode: PHImageRequestOptionsDeliveryMode,
resizeMode: PHImageRequestOptionsResizeMode,
completion: ((_ image: UIImage?, _ userInfo: [AnyHashable: Any]?) -> Void)?) {
getImagesQueue.async { [weak self] in
guard let self = self else { return }
let indexPath = IndexPath(item: index, section: albumId)
self.getAlbumData(id: albumId) { data in
_ = self.getImageSemaphore.wait(timeout: .now() + .seconds(3))
guard let photoAsset = data?.fetchResult.object(at: index) else { self.getImageSemaphore.signal(); return }
self.fetchImage(from: photoAsset,
userInfo: userInfo,
targetSize: targetSize,
deliveryMode: deliveryMode,
resizeMode: resizeMode) { [weak self] (image, userInfo) in
defer { self?.getImageSemaphore.signal() }
completion?(image, userInfo)
}
}
}
}
}
用法
private lazy var photoLibrary = PhotoService()
private var albums = [PhotoAlbumViewModel]()
//....
// Get albums
photoLibrary.getAllAlbums { [weak self] albums in
self?.albums = albums
// reload views
}
// Get photo
photoLibrary.getImage(albumId: albums[0].id,
index: 1, userInfo: nil,
targetSize: CGSize(width: 200, height: 200),
deliveryMode: .fastFormat,
resizeMode: .fast) { [weak self, weak cell] (image, userInfo) in
// reload views
}
完整示例（带有来自 PhotoLibrary 的图像的 collectionView）
ViewController.swift
import UIKit
import Photos
class ViewController: UIViewController {
private weak var collectionView: UICollectionView?
var collectionViewFlowLayout: UICollectionViewFlowLayout? {
return collectionView?.collectionViewLayout as? UICollectionViewFlowLayout
}
private lazy var photoLibrary = PhotoService()
private lazy var numberOfElementsInRow = 4
private lazy var cellIdentifier = "cellIdentifier"
private lazy var supplementaryViewIdentifier = "supplementaryViewIdentifier"
private var albums = [PhotoAlbumViewModel]()
private lazy var cellsTags = [IndexPath: Int]()
private lazy var tagKey = "cellTag"
private lazy var thumbnailImageSize = CGSize(width: 200, height: 200)
override func viewDidLoad() {
let collectionViewFlowLayout = UICollectionViewFlowLayout()
collectionViewFlowLayout.minimumLineSpacing = 5
collectionViewFlowLayout.minimumInteritemSpacing = 5
let _numberOfElementsInRow = CGFloat(numberOfElementsInRow)
let allWidthBetwenCells = _numberOfElementsInRow == 0 ? 0 : collectionViewFlowLayout.minimumInteritemSpacing*(_numberOfElementsInRow-1)
let width = (view.frame.width - allWidthBetwenCells)/_numberOfElementsInRow
collectionViewFlowLayout.itemSize = CGSize(width: width, height: width)
collectionViewFlowLayout.headerReferenceSize = CGSize(width: 0, height: 40)
let collectionView = UICollectionView(frame: .zero, collectionViewLayout: collectionViewFlowLayout)
view.addSubview(collectionView)
collectionView.translatesAutoresizingMaskIntoConstraints = false
collectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
collectionView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
collectionView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true
collectionView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor).isActive = true
collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: cellIdentifier)
collectionView.register(SupplementaryView.self,
forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
withReuseIdentifier: supplementaryViewIdentifier)
collectionView.backgroundColor = .white
self.collectionView = collectionView
collectionView.delegate = self
showAllPhotosButtonTouchedInside()
navigationItem.leftBarButtonItem = UIBarButtonItem(title: "All", style: .done, target: self,
action: #selector(showAllPhotosButtonTouchedInside))
navigationItem.rightBarButtonItem = UIBarButtonItem(title: "last 3", style: .done, target: self,
action: #selector(showLastSeveralPhotosButtonTouchedInside))
}
@objc func showAllPhotosButtonTouchedInside() {
photoLibrary.getAllAlbums { [weak self] albums in
self?.set(albums: albums)
if self?.collectionView?.dataSource == nil {
self?.collectionView?.dataSource = self
} else {
self?.collectionView?.reloadData()
}
}
}
@objc func showLastSeveralPhotosButtonTouchedInside() {
photoLibrary.getAllAlbums { [weak self] albums in
guard let firstAlbum = albums.first else { return }
var album: PhotoAlbumViewModel!
let maxPhotosToDisplay = 3
switch firstAlbum {
case .allPhotos(let id, let title, let count, let image, let isSelected):
let newCount = count > maxPhotosToDisplay ? maxPhotosToDisplay : count
album = .allPhotos(id: id, title: title, count: newCount, image: image, isSelected: isSelected)
case .regular(let id, let title, let count, let image, let isSelected):
let newCount = count > maxPhotosToDisplay ? maxPhotosToDisplay : count
album = .regular(id: id, title: title, count: newCount, image: image, isSelected: isSelected)
}
self?.set(albums: [album])
if self?.collectionView?.dataSource == nil {
self?.collectionView?.dataSource = self
} else {
self?.collectionView?.reloadData()
}
}
}
private func set(albums: [PhotoAlbumViewModel]) {
self.albums = albums
var counter = 0
for (section, album) in albums.enumerated() {
for row in 0..<album.count {
self.cellsTags[IndexPath(row: row, section: section)] = counter
counter += 1
}
}
}
}
extension ViewController: UICollectionViewDataSource {
func numberOfSections(in collectionView: UICollectionView) -> Int { return albums.count }
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return albums[section].count
}
func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: supplementaryViewIdentifier, for: indexPath) as! SupplementaryView
header.label?.text = albums[indexPath.section].title
return header
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CollectionViewCell
let tag = cellsTags[indexPath]!
cell.tag = tag
photoLibrary.getImage(albumId: albums[indexPath.section].id,
index: indexPath.item, userInfo: [tagKey: tag],
targetSize: thumbnailImageSize,
deliveryMode: .fastFormat,
resizeMode: .fast) { [weak self, weak cell] (image, userInfo) in
guard let cell = cell, let tagKey = self?.tagKey,
let cellTag = userInfo?[tagKey] as? Int,
cellTag == cell.tag else { return }
cell.imageView?.image = image
}
return cell
}
}
extension ViewController: UICollectionViewDelegate {}
CollectionViewCell.swift
import UIKit
class CollectionViewCell: UICollectionViewCell {
weak var imageView: UIImageView?
override init(frame: CGRect) {
super.init(frame: frame)
clipsToBounds = true
let imageView = UIImageView(frame: .zero)
imageView.contentMode = .scaleAspectFill
addSubview(imageView)
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.topAnchor.constraint(equalTo: topAnchor).isActive = true
imageView.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
imageView.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
imageView.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
self.imageView = imageView
backgroundColor = UIColor.lightGray.withAlphaComponent(0.3)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func prepareForReuse() {
super.prepareForReuse()
imageView?.image = nil
}
}
SupplementaryView.swift
import UIKit
class SupplementaryView: UICollectionReusableView {
weak var label: UILabel?
override init(frame: CGRect) {
super.init(frame: frame)
backgroundColor = .white
let label = UILabel(frame: frame)
label.textColor = .black
addSubview(label)
self.label = label
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func prepareForReuse() {
super.prepareForReuse()
self.label?.text = nil
}
}
故事板
结果
这是一个优雅的解决方案，效率在 Swift 4.
简而言之，我们请求一次最新的照片资源，然后在需要时将其转换为图像。
首先导入照片库：
import Photos
然后创建一个函数来获取最新拍摄的照片：
func fetchLatestPhotos(forCount count: Int?) -> PHFetchResult<PHAsset> {
// Create fetch options.
let options = PHFetchOptions()
// If count limit is specified.
if let count = count { options.fetchLimit = count }
// Add sortDescriptor so the lastest photos will be returned.
let sortDescriptor = NSSortDescriptor(key: "creationDate", ascending: false)
options.sortDescriptors = [sortDescriptor]
// Fetch the photos.
return PHAsset.fetchAssets(with: .image, options: options)
}
在您的情况下，您可能希望一次获取足够多的照片（例如 50 张），然后将结果存储在视图控制器中的某个位置：
var latestPhotoAssetsFetched: PHFetchResult<PHAsset>? = nil
在viewDidLoad中：
self.latestPhotoAssetsFetched = self.fetchLatestPhotos(forCount: 50)
最终在正确的位置请求图像（例如，集合视图单元格）：
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
/*
...your code to configure the cell...
*/
// Get the asset. If nothing, return the cell.
guard let asset = self.latestPhotoAssetsFetched?[indexPath.item] else {
return cell
}
// Here we bind the asset with the cell.
cell.representedAssetIdentifier = asset.localIdentifier
// Request the image.
PHImageManager.default().requestImage(for: asset,
targetSize: cell.imageView.frame.size,
contentMode: .aspectFill,
options: nil) { (image, _) in
// By the time the image is returned, the cell may has been recycled.
// We update the UI only when it is still on the screen.
if cell.representedAssetIdentifier == asset.localIdentifier {
cell.imageView.image = image
}
}
return cell
}
记得在您的单元格中添加一个 属性：
class PhotoCell: UICollectionViewCell {
var representedAssetIdentifier: String? = nil
}