将PHAsset从一张专辑移动/复制到另一张专辑 [英] Move/copy PHAsset from one album to another

问题描述

我想将资产从一张专辑转移到另一张专辑.但是我只能找到有关创建和删除资产的信息.我想移动而不是创建一个新副本并删除旧副本的原因是，我想保留资产的 localIdentifier 之类的数据位.如果我在另一个相册中重新创建资产，则会为它分配一个新的 localIdentifier ，对吗?

I want to move an asset from one album to another. But I could only find information on creating and deleting assets. The reason I want to move instead of creating a new one and deleting the old copy is, I want to preserve the bits of data like the localIdentifier of the asset. If I recreate an asset in another album, it will be assigned a new localIdentifier, am I right?

但是似乎不可能.因此，我至少采取了复制资产的措施.但这也给我带来了麻烦.

But it seems it's not possible. So I resorted to copying the asset at least. But it's giving me trouble as well.

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)
            }
        }
    })
}

该应用程序在 let assetPlaceholder = assetChangeRequest.placeholderForCreatedAsset！行崩溃，以查找 placeholderForCreatedAsset 的 nil 值.这意味着 PHAssetChangeRequest(forAsset:资产)仅可用于更改资产的元数据，而不能复制它.

The app crashes at the line let assetPlaceholder = assetChangeRequest.placeholderForCreatedAsset! for finding nil value for the placeholderForCreatedAsset. Which means PHAssetChangeRequest(forAsset: asset) can only be used to changing an asset's metadata and not duplicating it.

还有其他方法可以做到吗?有任何解决方法或破解方法吗?我将非常感谢您的帮助.

Is there any other way to do this? Any workaround or hack? I'll really appreciate any help.

推荐答案

没有什么比将资产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"中卷".相册仅包含对所有照片/相机胶卷"中原始照片/录像的引用.这意味着您可以将一张照片分配给n个相册.要管理这些分配，请查看 PHAssetCollectionChangeRequest 类.要在相册中添加一张或多张照片/录像，请使用 addAssets:，要从相册中删除资产，请使用 removeAssets:方法.

There is nothing like copying an asset from one album to another: In the iOS Photo Library all original photos/videos are located in "All Photos"/"Camera Roll". Albums contain only references to the original photo/video located in "All Photos/Camera Roll". This means you can assign one photo to n-Albums. To manage those assignments please have a look at the PHAssetCollectionChangeRequest class. To add one or several photos/video at an album use the addAssets:, to remove assets from an album use the removeAssets:method.

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