检查照片中是否存在图像答案

【问题标题】：Check if image exists in Photos检查照片中是否存在图像
【发布时间】：2016-07-27 22:15:31
【问题描述】：

我有一个由远程服务器管理的图像相册。我想为用户提供下载相册并将其存储到照片中的自定义相册的选项。但由于相册是动态的（照片被添加到其中），用户可以多次下载它。我不想多次下载相同的图片，只下载新的。

当我将图像存储在照片应用程序中时，是否可以关联一些元数据（唯一 ID）？然后检查该图像是否已经存在？

我正在使用 Photos Framework 来创建自定义相册并保存照片。

编辑：这是我创建自定义相册和保存照片的代码

/** Returns the first album from the photos app with the specified name. */
static func getAlbumWithName(name: String, completion: (album: PHAssetCollection?) -> Void) {

    let fetchOptions = PHFetchOptions()
    fetchOptions.predicate = NSPredicate(format: "localizedTitle = %@", name)
    let fetchResult = PHAssetCollection.fetchAssetCollectionsWithType(PHAssetCollectionType.Album, subtype: PHAssetCollectionSubtype.Any, options: fetchOptions)

    if fetchResult.count > 0 {

        guard let album = fetchResult.firstObject as? PHAssetCollection else {return}
        completion(album: album)

    } else {

        PHPhotoLibrary.sharedPhotoLibrary().performChanges({

            PHAssetCollectionChangeRequest.creationRequestForAssetCollectionWithTitle(name)

            }, completionHandler: { (result, error) in

                if result {

                    FileUtils.getAlbumWithName(name, completion: completion)

                } else {

                    completion(album: nil)

                }


        })

    }

}

/** Adds an image to the specified photos app album */
private static func addImage(image: UIImage, toAlbum album: PHAssetCollection, completion: ((status: Bool) -> Void)?) {

    PHPhotoLibrary.sharedPhotoLibrary().performChanges({

        let assetRequest = PHAssetChangeRequest.creationRequestForAssetFromImage(image)
        let assetPlaceholder = assetRequest.placeholderForCreatedAsset
        let albumChangeRequest = PHAssetCollectionChangeRequest(forAssetCollection: album)
        albumChangeRequest?.addAssets([assetPlaceholder!])


    }) { (status, error) in

        completion?(status: status)

    }

}

【问题讨论】：

编辑您的问题以显示您如何将照片下载和保存到此自定义相册的代码可能很有用

标签： ios swift

【解决方案1】：

您需要做的就是从资产占位符中读取“localIdentifier”。我已经扩充了您的代码以在完成处理程序中返回标识符。您可能想处理这些选项。

private static func addImage(image: UIImage, toAlbum album: PHAssetCollection, completion: ((status: Bool, identifier: String?) -> Void)?) {

    var localIdentifier: String?
    PHPhotoLibrary.sharedPhotoLibrary().performChanges({

        let assetRequest = PHAssetChangeRequest.creationRequestForAssetFromImage(image)
        let assetPlaceholder = assetRequest.placeholderForCreatedAsset
        let albumChangeRequest = PHAssetCollectionChangeRequest(forAssetCollection: album)
        albumChangeRequest?.addAssets([assetPlaceholder!])
        localIdentifier = assetPlaceholder?.localIdentifier

    }) { (status, error) in

        completion?(status: status, identifier: localIdentifier)

    }
}

当您想再次读取该资产时，您的加载图像方法可能看起来像这样（我没有使用您的约定或变量名称）。这将同步读取资产，但我相信您可以发现异步选项。

internal func loadPhoto(identifier: String) -> UIImage? {
    if assetCollection == nil {
        return nil
    }

    let fetchOptions = PHFetchOptions()
    fetchOptions.predicate = NSPredicate(format: "localIdentifier = %@", identifier)
    let fetchResult = PHAsset.fetchAssetsInAssetCollection(assetCollection, options: fetchOptions)
    if fetchResult.count > 0 {
        if let asset = fetchResult.firstObject as? PHAsset {
            let options = PHImageRequestOptions()
            options.deliveryMode = .HighQualityFormat
            options.synchronous = true
            var result: UIImage?
            PHImageManager.defaultManager().requestImageForAsset(asset, targetSize: CGSize(width: asset.pixelWidth, height: asset.pixelHeight), contentMode: .AspectFit, options: options, resultHandler: {(image: UIImage?, _: [NSObject: AnyObject]?) -> Void in
                result = image
            })
            return result
        }
    }
    return nil
}

【讨论】：