Improve the performance and speed of loading large numbers of assets

AssetsPickerViewController/Classes/Assets/AssetsManager+Sync.swift

@@ -99,7 +99,8 @@ extension AssetsManager: PHPhotoLibraryChangeObserver {
                     let removedIndexes = removedIndexesSet.asArray().sorted(by: { $0.row < $1.row })
                     var removedAssets = [PHAsset]()
                     for removedIndex in removedIndexes.reversed() {
-                        removedAssets.insert(assetArray.remove(at: removedIndex.row), at: 0)
+//                        removedAssets.insert(assetArray.remove(at: removedIndex.row), at: 0)
+                        // TODO: replace assetArray to fetchResult
                     }
                     // stop caching for removed assets
                     stopCache(assets: removedAssets, size: pickerConfig.assetCacheSize)
@@ -112,7 +113,8 @@ extension AssetsManager: PHPhotoLibraryChangeObserver {
                     for insertedIndex in insertedIndexes {
                         let insertedAsset = assetsChangeDetails.fetchResultAfterChanges.object(at: insertedIndex.row)
                         insertedAssets.append(insertedAsset)
-                        assetArray.insert(insertedAsset, at: insertedIndex.row)
+//                        assetArray.insert(insertedAsset, at: insertedIndex.row)
+                        // TODO: replace assetArray to fetchResult
                     }
                     // start caching for inserted assets
                     cache(assets: insertedAssets, size: pickerConfig.assetCacheSize)

AssetsPickerViewController/Classes/Assets/AssetsManager.swift

@@ -37,7 +37,7 @@ open class AssetsManager: NSObject {
         }
     }
 
-    fileprivate let imageManager = PHCachingImageManager()
+    let imageManager = PHCachingImageManager()
     fileprivate var authorizationStatus = PHPhotoLibrary.authorizationStatus()
     var subscribers = [AssetsManagerDelegate]()
 
@@ -50,14 +50,14 @@ open class AssetsManager: NSObject {
     var fetchedAlbumsArray = [[PHAssetCollection]]()
     /// stores sorted array by applying user defined comparator, it's in decreasing order by count by default, and it might same as fetchedAlbumsArray if AssetsPickerConfig has  albumFetchOptions without albumComparator
     var sortedAlbumsArray = [[PHAssetCollection]]()
-    internal(set) open var assetArray = [PHAsset]()
+    internal(set) open var fetchResult: PHFetchResult<PHAsset>?
 
     fileprivate(set) open var defaultAlbum: PHAssetCollection?
     fileprivate(set) open var cameraRollAlbum: PHAssetCollection!
     fileprivate(set) open var selectedAlbum: PHAssetCollection?
 
     fileprivate var isFetchedAlbums: Bool = false
-    fileprivate var resourceLoadingQueue: DispatchQueue = DispatchQueue(label: "com.assetspicker.loader", qos: .userInitiated)
+    fileprivate var resourceLoadingQueue: DispatchQueue = DispatchQueue(label: "com.assetspicker.loader", qos: .default)
 
     private override init() {
         super.init()
@@ -82,7 +82,7 @@ open class AssetsManager: NSObject {
         sortedAlbumsArray.removeAll()
 
         // clear assets
-        assetArray.removeAll()
+        fetchResult = nil
 
         // clear fetch results
         albumsFetchArray.removeAll()
@@ -236,8 +236,9 @@ extension AssetsManager {
     open func image(at index: Int, size: CGSize, isNeedDegraded: Bool = true, completion: @escaping ((UIImage?, Bool) -> Void)) -> PHImageRequestID {
         let options = PHImageRequestOptions()
         options.isNetworkAccessAllowed = true
+        guard let asset = fetchResult?.object(at: index) else { return PHInvalidImageRequestID }
         return imageManager.requestImage(
-            for: assetArray[index],
+            for: asset,
             targetSize: size,
             contentMode: .aspectFill,
             options: options,
@@ -318,13 +319,14 @@ extension AssetsManager {
             return false
         }
         self.selectedAlbum = newAlbum
-        if let fetchResult = fetchMap[newAlbum.localIdentifier] {
-            let indexSet = IndexSet(0..<fetchResult.count)
-            assetArray = fetchResult.objects(at: indexSet)
-            return true
-        } else {
+        guard let album = AssetsManager.shared.selectedAlbum else {
+            return false
+        }
+        guard let fetchResult = AssetsManager.shared.fetchMap[album.localIdentifier] else {
             return false
         }
+        self.fetchResult = fetchResult
+        return true
     }
 
     open func selectDefaultAlbum() {
@@ -341,24 +343,20 @@ extension AssetsManager {
         }
     }
 
-    open func selectAsync(album newAlbum: PHAssetCollection, completion: @escaping (Bool, [PHAsset]) -> Void) {
+    open func selectAsync(album newAlbum: PHAssetCollection, completion: @escaping (Bool, PHFetchResult<PHAsset>?) -> Void) {
         if let oldAlbumIdentifier = self.selectedAlbum?.localIdentifier, oldAlbumIdentifier == newAlbum.localIdentifier {
             logi("Selected same album.")
-            completion(false, [])
+            completion(false, nil)
         }
         self.selectedAlbum = newAlbum
-        if let fetchResult = fetchMap[newAlbum.localIdentifier] {
-            resourceLoadingQueue.async { [weak self] in
-                let indexSet = IndexSet(0..<fetchResult.count)
-                let photos = fetchResult.objects(at: indexSet)
-                self?.assetArray = photos
-                DispatchQueue.main.async {
-                    completion(true, photos)
-                }
-            }
-        } else {
-            completion(false, [])
+        guard let album = AssetsManager.shared.selectedAlbum else { completion(false, nil)
+            return
+        }
+        guard let fetchResult = AssetsManager.shared.fetchMap[album.localIdentifier] else { completion(false, nil)
+            return
         }
+        self.fetchResult = fetchResult
+        completion(true, fetchResult)
     }
 }
 
@@ -515,18 +513,18 @@ extension AssetsManager {
         }
     }
 
-    open func fetchAssets(isRefetch: Bool = false, completion: (([PHAsset]) -> Void)? = nil) {
+    open func fetchAssets(isRefetch: Bool = false, completion: ((PHFetchResult<PHAsset>?) -> Void)? = nil) {
 
         fetchAlbums(isRefetch: isRefetch, completion: { [weak self] _ in
 
             guard let `self` = self else { return }
             if isRefetch {
-                self.assetArray.removeAll()
+                self.fetchResult = nil
             }
 
             // set default album
-            self.selectAsync(album: self.defaultAlbum ?? self.cameraRollAlbum) { result, photos in
-                completion?(photos)
+            self.selectAsync(album: self.defaultAlbum ?? self.cameraRollAlbum) { successful, result in
+                completion?(result)
             }
         })
 
@@ -538,7 +536,10 @@ extension AssetsManager {
         let albumFetchResult = PHAssetCollection.fetchAssetCollections(with: type, subtype: .any, options: fetchOption)
         var fetchedAlbums = [PHAssetCollection]()
 
-        albumFetchResult.enumerateObjects({ (album, _, _) in
+        let indexSet = IndexSet(integersIn: 0..<albumFetchResult.count)
+        let albums = albumFetchResult.objects(at: indexSet)
+
+        for album in albums {
             // fetch assets
             self.fetchAlbum(album: album)
 
@@ -551,7 +552,7 @@ extension AssetsManager {
                 self.cameraRollAlbum = album
             }
             fetchedAlbums.append(album)
-        })
+        }
 
         // get sorted albums
         let sortedAlbums = self.sortedAlbums(fromAlbums: fetchedAlbums)

AssetsPickerViewController/Classes/Photo/Controller/AssetsPhotoViewController+AssetsManager.swift

@@ -100,11 +100,18 @@ extension AssetsPhotoViewController {
                 completion(nil)
                 return
             }
-            guard let savedAssetEntry = AssetsManager.shared.assetArray.enumerated().first(where: { $0.element.localIdentifier == newlySavedIdentifier }) else {
-                completion(nil)
+            var index: Int = NSNotFound
+            guard let fetchResult = AssetsManager.shared.fetchResult else { return }
+            fetchResult.enumerateObjects { (asset, idx, stop) in
+                if asset.localIdentifier == newlySavedIdentifier {
+                    index = idx
+                    stop.pointee = true
+                }
+            }
+            if index == NSNotFound {
                 return
             }
-            let ip = IndexPath(row: savedAssetEntry.offset, section: 0)
+            let ip = IndexPath(row: index, section: 0)
             indexPathToSelect = ip
             if selectedArray.count < pickerConfig.assetsMaximumSelectionCount {
                 select(at: ip)

AssetsPickerViewController/Classes/Photo/Controller/AssetsPhotoViewController+Collection.swift

@@ -12,7 +12,7 @@ import Photos
 extension AssetsPhotoViewController: UICollectionViewDataSource {
 
     public func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
-        let count = AssetsManager.shared.assetArray.count
+        let count = AssetsManager.shared.fetchResult?.count ?? 0
         updateEmptyView(count: count)
         return count
     }
@@ -23,11 +23,14 @@ extension AssetsPhotoViewController: UICollectionViewDataSource {
             logw("Failed to cast UICollectionViewCell.")
             return cell
         }
-        let asset = AssetsManager.shared.assetArray[indexPath.row]
-        photoCell.asset = asset
-        photoCell.isVideo = asset.mediaType == .video
-        if photoCell.isVideo {
-            photoCell.duration = asset.duration
+        if let asset = AssetsManager.shared.fetchResult?.object(at: indexPath.row) {
+            photoCell.asset = asset
+            photoCell.isVideo = asset.mediaType == .video
+            if photoCell.isVideo {
+                photoCell.duration = asset.duration
+            }
+        } else {
+            photoCell.asset = nil
         }
         return cell
     }
@@ -40,17 +43,20 @@ extension AssetsPhotoViewController: UICollectionViewDataSource {
             return
         }
 
-        let asset = AssetsManager.shared.assetArray[indexPath.row]
-        photoCell.asset = asset
-        photoCell.isVideo = asset.mediaType == .video
-        if photoCell.isVideo {
-            photoCell.duration = asset.duration
-        }
-
-        if let selectedAsset = selectedMap[asset.localIdentifier] {
-            if let targetIndex = selectedArray.firstIndex(of: selectedAsset) {
-                photoCell.count = targetIndex + 1
+        if let asset = AssetsManager.shared.fetchResult?.object(at: indexPath.row) {
+            photoCell.asset = asset
+            photoCell.isVideo = asset.mediaType == .video
+            if photoCell.isVideo {
+                photoCell.duration = asset.duration
             }
+
+            if let selectedAsset = selectedMap[asset.localIdentifier] {
+                if let targetIndex = selectedArray.firstIndex(of: selectedAsset) {
+                    photoCell.count = targetIndex + 1
+                }
+            }
+        } else {
+            photoCell.asset = nil
         }
 
         fetchService.cancelFetching(at: indexPath)
@@ -114,8 +120,10 @@ extension AssetsPhotoViewController: UICollectionViewDataSourcePrefetching {
     public func collectionView(_ collectionView: UICollectionView, prefetchItemsAt indexPaths: [IndexPath]) {
         var assets = [PHAsset]()
         for indexPath in indexPaths {
-            if AssetsManager.shared.assetArray.count > indexPath.row {
-                assets.append(AssetsManager.shared.assetArray[indexPath.row])
+            let count = AssetsManager.shared.fetchResult?.count ?? 0
+            if count > indexPath.row {
+                guard let asset = AssetsManager.shared.fetchResult?.object(at: indexPath.row) else { return }
+                assets.append(asset)
             }
         }
         AssetsManager.shared.cache(assets: assets, size: pickerConfig.assetCacheSize)

AssetsPickerViewController/Classes/Photo/Controller/AssetsPhotoViewController+Delegate.swift

@@ -74,7 +74,8 @@ extension AssetsPhotoViewController: UIViewControllerPreviewingDelegate {
         guard let pressingCell = collectionView.cellForItem(at: pressingIndexPath) else { return nil }
         previewingContext.sourceRect = pressingCell.frame
         let previewController = AssetsPreviewController()
-        previewController.asset = AssetsManager.shared.assetArray[pressingIndexPath.row]
+        guard let fetchResult = AssetsManager.shared.fetchResult else { return nil }
+        previewController.asset = fetchResult.object(at: pressingIndexPath.row)
         return previewController
     }
 

AssetsPickerViewController/Classes/Photo/Controller/AssetsPhotoViewController+Model.swift

@@ -36,8 +36,10 @@ extension AssetsPhotoViewController {
 
     func isSelected(at indexPath: IndexPath) -> Bool {
         let manager = AssetsManager.shared
-        guard indexPath.row < manager.assetArray.count else { return false }
-        if let _ = selectedMap[manager.assetArray[indexPath.row].localIdentifier] {
+        guard let fetchResult = manager.fetchResult else { return false }
+        guard indexPath.row < fetchResult.count else { return false }
+        let asset = fetchResult.object(at: indexPath.row)
+        if let _ = selectedMap[asset.localIdentifier] {
             return true
         } else {
             return false
@@ -47,8 +49,9 @@ extension AssetsPhotoViewController {
     func select(at indexPath: IndexPath) {
         defer { logSelectStatus(indexPath, isSelect: true) }
         let manager = AssetsManager.shared
-        guard indexPath.row < manager.assetArray.count else { return }
-        let asset = manager.assetArray[indexPath.row]
+        guard let fetchResult = manager.fetchResult else { return }
+        guard indexPath.row < fetchResult.count else { return }
+        let asset = fetchResult.object(at: indexPath.row)
         if let _ = selectedMap[asset.localIdentifier] {} else {
             selectedArray.append(asset)
             selectedMap[asset.localIdentifier] = asset
@@ -61,8 +64,9 @@ extension AssetsPhotoViewController {
     func deselect(at indexPath: IndexPath) {
         defer { logSelectStatus(indexPath, isSelect: false) }
         let manager = AssetsManager.shared
-        guard indexPath.row < manager.assetArray.count else { return }
-        let asset = manager.assetArray[indexPath.row]
+        guard let fetchResult = manager.fetchResult else { return }
+        guard indexPath.row < fetchResult.count else { return }
+        let asset = fetchResult.object(at: indexPath.row)
         guard let targetAsset = selectedMap[asset.localIdentifier] else {
             logw("Invalid status.")
             return

AssetsPickerViewController/Classes/Photo/Controller/AssetsPhotoViewController+Selection.swift

@@ -32,7 +32,8 @@ extension AssetsPhotoViewController: UICollectionViewDelegate {
         if LogConfig.isSelectLogEnabled { logi("shouldSelectItemAt: \(indexPath.row)") }
 
         if let delegate = self.delegate {
-            let shouldSelect = delegate.assetsPicker?(controller: picker, shouldSelect: AssetsManager.shared.assetArray[indexPath.row], at: indexPath) ?? true
+            guard let fetchResult = AssetsManager.shared.fetchResult else { return false }
+            let shouldSelect = delegate.assetsPicker?(controller: picker, shouldSelect: fetchResult.object(at: indexPath.row), at: indexPath) ?? true
             guard shouldSelect else { return false }
         }
 
@@ -62,7 +63,8 @@ extension AssetsPhotoViewController: UICollectionViewDelegate {
     public func collectionView(_ collectionView: UICollectionView, shouldDeselectItemAt indexPath: IndexPath) -> Bool {
         if LogConfig.isSelectLogEnabled { logi("shouldDeselectItemAt: \(indexPath.row)") }
         if let delegate = self.delegate {
-            let shouldDeselect = delegate.assetsPicker?(controller: picker, shouldDeselect: AssetsManager.shared.assetArray[indexPath.row], at: indexPath) ?? true
+            guard let fetchResult = AssetsManager.shared.fetchResult else { return false }
+            let shouldDeselect = delegate.assetsPicker?(controller: picker, shouldDeselect: fetchResult.object(at: indexPath.row), at: indexPath) ?? true
             guard shouldDeselect else { return false }
         }
         deselect(at: indexPath)
@@ -86,7 +88,8 @@ extension AssetsPhotoViewController {
                 return
             }
             for selectedIndexPath in indexPathsForSelectedItems {
-                if let _ = selectedMap[AssetsManager.shared.assetArray[selectedIndexPath.row].localIdentifier] {
+                guard let fetchResult = AssetsManager.shared.fetchResult else { return }
+                if let _ = selectedMap[fetchResult.object(at: selectedIndexPath.row).localIdentifier] {
 
                 } else {
                     loge("selected item not found in local map!")

AssetsPickerViewController/Classes/Photo/Controller/AssetsPhotoViewController+Setup.swift

@@ -73,12 +73,13 @@ extension AssetsPhotoViewController {
         let manager = AssetsManager.shared
         manager.subscribe(subscriber: self)
         manager.fetchAlbums { _ in
-            manager.fetchAssets() { [weak self] photos in
+            manager.fetchAssets() { [weak self] result in
                 guard let `self` = self else { return }
-                self.updateEmptyView(count: photos.count)
+                guard let fetchResult = result else { return }
+                self.updateEmptyView(count: fetchResult.count)
                 self.updateNavigationStatus()
                 self.collectionView.reloadData()
-                self.preselectItemsIfNeeded(photos: photos)
+                self.preselectItemsIfNeeded(result: fetchResult)
                 self.scrollToLastItemIfNeeded()
                 // hide loading
                 self.loadingPlaceholderView.isHidden = true