快速检测从照片库中删除的图像

Question

我正在保存照片库图像的 PHAsset 的本地标识符并显示这些 集合视图中的图像。我的问题是当我从照片库中删除图像时 然后我的应用程序崩溃，因为它无法获取已删除的 PHAsset 从照片库。这是我显示资产的代码：

 func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = photoCollectionView.dequeueReusableCell(withReuseIdentifier: "imageShowCell", for: indexPath) as! imageShowCell
     let image = photoArray.object(at: indexPath.item) as! Photos
     let imageManager = PHImageManager()
     let asset = PHAsset.fetchAssets(withLocalIdentifiers: [image.pic_name!], options: nil)[0]
    let scale  = UIScreen.main.scale
    let size = CGSize(width: 50.0 * scale, height: 50.0 * scale)
    imageManager.requestImage(for: asset, targetSize: size, contentMode: .aspectFill, options: nil) { (image, _) in
        cell.imageView.image  = image
    }
    return cell
}

Answer 1

您需要向照片库注册变更观察者。然后，您会在照片被删除、插入、更改或移动时收到通知。观察者需要继承自PHPhotoLibraryChangeObserver。然后你需要实现函数photoLibraryDidChange(_ changeInstance: PHChange)。如果您使用视图控制器作为观察者，您应该能够捕获集合视图中的所有更改，如下所示。下面的示例假设您拥有一个集合视图所需的所有 phAsset 数组，以显示其随时可用的图像

class MyViewController : UIViewController, PHPhotoLibraryChangeObserver {

    func viewDidLoad() {
        ...
        PHPhotoLibrary.shared().register(self)
        ...
    }

    func photoLibraryDidChange(_ changeInstance: PHChange) {
        // Change notifications may be made on a background queue.
        // Re-dispatch to the main queue to update the UI.
        // Check for changes to the displayed album itself
        // (its existence and metadata, not its member self).
        guard let photos = photos else {return}

        // Check for changes to the list of assets (insertions, deletions, moves, or updates).
        if let changes = changeInstance.changeDetails(for: photos) {
            // Keep the new fetch result for future use.
            photos = changes.fetchResultAfterChanges
            if changes.hasIncrementalChanges {
                // If there are incremental diffs, animate them in the collection view.
                self.collectionView.performBatchUpdates({
                    // For indexes to make sense, updates must be in this order:
                    // delete, insert, reload, move
                    if let removed = changes.removedIndexes, removed.count > 0 {
                        print("photoLibraryDidChange: Delete at \(removed.map { IndexPath(item: $0, section:0) })")
                        self.collectionView.deleteItems(at: removed.map { IndexPath(item: $0, section:0) })
                    }
                    if let inserted = changes.insertedIndexes, inserted.count > 0 {
                        print("photoLibraryDidChange: Insert at \(inserted.map { IndexPath(item: $0, section:0) })")
                        self.collectionView.insertItems(at: inserted.map { IndexPath(item: $0, section:0) })
                    }
                    if var changed = changes.changedIndexes, changed.count > 0 {
                        print("photoLibraryDidChange: Reload at \(changed.map { IndexPath(item: $0, section:0) })")
                        // subtract removed indices
                        if let removed = changes.removedIndexes {
                            changed.subtract(removed)
                        }
                        self.collectionView.reloadItems(at: changed.map { IndexPath(item: $0, section:0) })
                    }
                    changes.enumerateMoves { fromIndex, toIndex in
                        print("photoLibraryDidChange: Move at \(IndexPath(item: fromIndex, section:0)) to \(IndexPath(item: toIndex, section:0 ))")
                        self.collectionView.moveItem(at: IndexPath(item: fromIndex, section: 0), to: IndexPath(item: toIndex, section: 0))
                    }
                })

            } else {
                // Reload the collection view if incremental diffs are not available.
                ...
            }
        }

    }

    var photos : PHFetchResult<PHAsset>?
    weak var collectionView : UICollectionView!
}

目前您正在临时创建 PHAsset。您需要某种形式的永久 PHObject 才能使上述功能发挥作用。如果您将单个 PHAsset 存储在您的 photoArray 对象中，您可以在每个 PHAsset 上使用PHChange.changeDetails(for object: PHObject) 来捕获它们是否在应用程序运行时被删除。但是，这在应用程序的会话之间不起作用。

您可以创建一个相册并将您的应用使用的所有图像存储在该相册中，而不是存储一组本地标识符。然后您可以查看该专辑的更改。

顺便说一句，您遇到崩溃的原因是您要求空数组的数组元素 [0]。您可以通过检查 PHAsset.fetchAssets() 调用的结果是否计数大于零来避免崩溃。