将PHAsset从一个相册移动/复制到另一个相册

Question

我想将资产从一个相册移动到另一个相册。但我只能找到有关创建和删除资产的信息。我想要移动而不是创建新的和删除旧拷贝的原因是，我想保留像资产的localIdentifier这样的数据位。如果我在另一个相册中重新创建一个资源，它将被分配一个新的localIdentifier，对吗？

但这似乎是不可能的。因此，我至少采取了复制资产的方式。但它也给我带来了麻烦。

这是我的代码。

func copyAsset() {
    if let assets = getAssetsFromCollection(collectionTitle: "Old") {
        if getAssetColection("New") == nil {
            createCollection("New") { collection in
                if let collection = collection {
                    print("Collection created")
                    self.copyAssetsToCollection(assets, toCollection: collection)
                }
            }
        }
    }
}

/**
 Copy assets to album.

 - parameter assets:     Array of assets to copy.
 - parameter collection: The collection where the assets need to be copied.
 */
func copyAssetsToCollection(assets: [PHAsset], toCollection collection: PHAssetCollection) {
    PHPhotoLibrary.sharedPhotoLibrary().performChanges({
        let asset = assets.first!
        print(asset.localIdentifier)
        let assetChangeRequest = PHAssetChangeRequest(forAsset: asset)
        let assetPlaceholder = assetChangeRequest.placeholderForCreatedAsset!

        let collectionChangeRequest = PHAssetCollectionChangeRequest(forAssetCollection: collection)!
        collectionChangeRequest.addAssets([assetPlaceholder])
    }, completionHandler: { success, error in
        if success {
            print("Photo copied to collection")
        } else {
            if let error = error {
                print("Error adding photos to collection: \(error.code) - \(error.localizedDescription)")
            }
        }
    })
}

/**
 Retrieve the album for the given title.

 - parameter title: Album title.

 - returns: Album if it exists. nil if it doesn't.
 */
func getAssetColection(title: String) -> PHAssetCollection? {
    let fetchOptions = PHFetchOptions()
    fetchOptions.predicate = NSPredicate(format: "title ==[cd] %@", title)
    if let collection = PHAssetCollection.fetchAssetCollectionsWithType(.Album, subtype: .AlbumRegular, options: fetchOptions).firstObject {
        return collection as? PHAssetCollection
    }
    return nil
}

/**
 Get assets from a given album.

 - parameter title: Album title.

 - returns: An array of assets if they exist. nil if they don't.
 */
func getAssetsFromCollection(collectionTitle title: String) -> [PHAsset]? {
    var assets = [PHAsset]()
    if let collection = getAssetColection(title) {
        let fetchOptions = PHFetchOptions()
        fetchOptions.predicate = NSPredicate(format: "mediaType == %d", PHAssetMediaType.Image.rawValue)
        let fetchResult = PHAsset.fetchAssetsInAssetCollection(collection, options: fetchOptions)
        fetchResult.enumerateObjectsUsingBlock { object, index, stop in
            if let asset = object as? PHAsset {
                assets.append(asset)
            }
        }
        return assets
    }
    return nil
}

/**
 Create an album in Photos app.

 - parameter title:      Album title.
 - parameter completion: Album if successfully created. nil if it fails.
 */
func createCollection(title: String, completion: (collection: PHAssetCollection?) -> ()) {
    var albumPlaceholder: PHObjectPlaceholder!
    PHPhotoLibrary.sharedPhotoLibrary().performChanges({
        let request = PHAssetCollectionChangeRequest.creationRequestForAssetCollectionWithTitle(title)
        albumPlaceholder = request.placeholderForCreatedAssetCollection
    }, completionHandler: { success, error in
        if success {
            let fetchResult = PHAssetCollection.fetchAssetCollectionsWithLocalIdentifiers([albumPlaceholder.localIdentifier], options: nil)
            completion(collection: fetchResult.firstObject as? PHAssetCollection)
        } else {
            if let error = error {
                print("Failed to create album: \(title) in Photos app: \(error.code) - \(error.localizedDescription)")
                completion(collection: nil)
            }
        }
    })
}

应用程序在查找placeholderForCreatedAsset的nil值的let assetPlaceholder = assetChangeRequest.placeholderForCreatedAsset!行崩溃。这意味着PHAssetChangeRequest(forAsset: asset)只能用于更改资产的元数据，而不能复制它。

有没有其他方法可以做到这一点？有什么变通或破解方法吗？我真的很感谢任何人的帮助。

Answer 1

没有什么比将资源从一个相册复制到另一个相册更好的了:在iOS照片库中，所有原始照片/视频都位于“所有照片”/“相机卷轴”中。相册只包含位于“所有照片/相机胶卷”中的原始照片/视频的引用。这意味着您可以将一张照片分配给n个相册。要管理这些作业，请查看PHAssetCollectionChangeRequest类。要在相册中添加一个或多个照片/视频，请使用addAssets:；要从相册中删除资产，请使用removeAssets:方法。