apple document

PHPhotoLibraryChangeObserver.swift

extension TLPhotosPickerViewController: PHPhotoLibraryChangeObserver {
    public func photoLibraryDidChange(_ changeInstance: PHChange) {
        guard getfocusedIndex() == 0 else { return }
        let addIndex = self.usedCameraButton ? 1 : 0
        DispatchQueue.main.sync {
            guard let changeFetchResult = self.focusedCollection?.fetchResult else { return }
            guard let changes = changeInstance.changeDetails(for: changeFetchResult) else { return }
            if changes.hasIncrementalChanges {
                var deletedSelectedAssets = false
                var order = 0
                #if swift(>=4.1)
                self.selectedAssets = self.selectedAssets.enumerated().compactMap({ (offset,asset) -> TLPHAsset? in
                    var asset = asset
                    if let phAsset = asset.phAsset, changes.fetchResultAfterChanges.contains(phAsset) {
                        order += 1
                        asset.selectedOrder = order
                        return asset
                    }
                    deletedSelectedAssets = true
                    return nil
                })
                #else
                self.selectedAssets = self.selectedAssets.enumerated().flatMap({ (offset,asset) -> TLPHAsset? in
                    var asset = asset
                    if let phAsset = asset.phAsset, changes.fetchResultAfterChanges.contains(phAsset) {
                        order += 1
                        asset.selectedOrder = order
                        return asset
                    }
                    deletedSelectedAssets = true
                    return nil
                })
                #endif
                if deletedSelectedAssets {
                    self.focusedCollection?.fetchResult = changes.fetchResultAfterChanges
                    self.collectionView.reloadData()
                }else {
                    self.collectionView.performBatchUpdates({ [weak self] in
                        guard let `self` = self else { return }
                        self.focusedCollection?.fetchResult = changes.fetchResultAfterChanges
                        if let removed = changes.removedIndexes, removed.count > 0 {
                            self.collectionView.deleteItems(at: removed.map { IndexPath(item: $0+addIndex, section:0) })
                        }
                        if let inserted = changes.insertedIndexes, inserted.count > 0 {
                            self.collectionView.insertItems(at: inserted.map { IndexPath(item: $0+addIndex, section:0) })
                        }
                        if let changed = changes.changedIndexes, changed.count > 0 {
                            self.collectionView.reloadItems(at: changed.map { IndexPath(item: $0+addIndex, section:0) })
                        }
                        changes.enumerateMoves { fromIndex, toIndex in
                            self.collectionView.moveItem(at: IndexPath(item: fromIndex, section: 0),
                                                         to: IndexPath(item: toIndex, section: 0))
                        }
                    })
                }
            }else {
                self.focusedCollection?.fetchResult = changes.fetchResultAfterChanges
                self.collectionView.reloadData()
            }
            if let collection = self.focusedCollection {
                self.collections[getfocusedIndex()] = collection
                self.albumPopView.tableView.reloadRows(at: [IndexPath(row: getfocusedIndex(), section: 0)], with: .none)
            }
        }
    }
}