How to fetch album poster image using Photo Kit?

Question

When using Assets Library you could fetch the album's poster image from ALAssetsGroup. How do you achieve the same when using Photos Framework (Photo kit)?

Answer 1

I do it this way. In the method cellForRowAtIndexPath: in albums tableView add the following code.

Objective C:

    PHFetchOptions *fetchOptions = [[PHFetchOptions alloc] init];
    fetchOptions.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"creationDate" ascending:YES]];
    PHFetchResult *fetchResult = [PHAsset fetchKeyAssetsInAssetCollection:[self.assetCollections objectAtIndex:indexPath.row] options:fetchOptions];
        PHAsset *asset = [fetchResult firstObject];
        PHImageRequestOptions *options = [[PHImageRequestOptions alloc] init];
        options.resizeMode = PHImageRequestOptionsResizeModeExact;

        CGFloat scale = [UIScreen mainScreen].scale;
        CGFloat dimension = 78.0f;
        CGSize size = CGSizeMake(dimension*scale, dimension*scale);

        [[PHImageManager defaultManager] requestImageForAsset:asset targetSize:size contentMode:PHImageContentModeAspectFill options:options resultHandler:^(UIImage *result, NSDictionary *info) {
        dispatch_async(dispatch_get_main_queue(), ^{
            cell.imageView.image = result;
        });

        }];

Swift 3:

let fetchOptions = PHFetchOptions()
let descriptor = NSSortDescriptor(key: "creationDate", ascending: true)
fetchOptions.sortDescriptors = [descriptor]

let fetchResult = PHAsset.fetchKeyAssets(in: assets[indexPath.row], options: fetchOptions)

guard let asset = fetchResult?.firstObject else {
    return
}

let options = PHImageRequestOptions()
options.resizeMode = .exact

let scale = UIScreen.main.scale
let dimension = CGFloat(78.0)
let size = CGSize(width: dimension * scale, height: dimension * scale)


PHImageManager.default().requestImage(for: asset, targetSize: size, contentMode: .aspectFill, options: options) { (image, info) in
    DispatchQueue.main.async {
        cell.imageView.image = image
    }
}

Edit: Looks like fetchKeyAssetsInAssetCollection does not always return correct results (most recently captured images/videos). The definition of keyAssets is vaguely defined by apple. Better use

+ (PHFetchResult *)fetchAssetsInAssetCollection:(PHAssetCollection *)assetCollection options:(PHFetchOptions *)options

to get the fetch results array and then get the firstObject from the fetch results as described before. This will certainly return the correct results. :)

Answer 2

Here's what I'm using now. It handles different types of photo collections and the case when key asset is missing.

static func fetchThumbnail(collection: PHCollection, targetSize: CGSize, completion: @escaping (UIImage?) -> ()) {

    func fetchAsset(asset: PHAsset, targetSize: CGSize, completion: @escaping (UIImage?) -> ()) {
        let options = PHImageRequestOptions()
        options.deliveryMode = PHImageRequestOptionsDeliveryMode.highQualityFormat
        options.isSynchronous = false
        options.isNetworkAccessAllowed = true

        // We could use PHCachingImageManager for better performance here
        PHImageManager.default().requestImage(for: asset, targetSize: targetSize, contentMode: .default, options: options, resultHandler: { (image, info) in
            completion(image)
        })
    }

    func fetchFirstImageThumbnail(collection: PHAssetCollection, targetSize: CGSize, completion: @escaping (UIImage?) -> ()) {
        // We could sort by creation date here if we want
        let assets = PHAsset.fetchAssets(in: collection, options: PHFetchOptions())
        if let asset = assets.firstObject {
            fetchAsset(asset: asset, targetSize: targetSize, completion: completion)
        } else {
            completion(nil)
        }
    }

    if let collection = collection as? PHAssetCollection {
        let assets = PHAsset.fetchKeyAssets(in: collection, options: PHFetchOptions())

        if let keyAsset = assets?.firstObject {
            fetchAsset(asset: keyAsset, targetSize: targetSize) { (image) in
                if let image = image {
                    completion(image)
                } else {
                    fetchFirstImageThumbnail(collection: collection, targetSize: targetSize, completion: completion)
                }
            }
        } else {
            fetchFirstImageThumbnail(collection: collection, targetSize: targetSize, completion: completion)
        }
    } else if let collection = collection as? PHCollectionList {
        // For folders we get the first available thumbnail from sub-folders/albums
        // possible improvement - make a "tile" thumbnail with 4 images
        let inner = PHCollection.fetchCollections(in: collection, options: PHFetchOptions())
        inner.enumerateObjects { (innerCollection, idx, stop) in
            self.fetchThumbnail(collection: innerCollection, targetSize: targetSize, completion: { (image) in
                if image != nil {
                    completion(image)
                    stop.pointee = true
                } else if idx >= inner.count - 1 {
                    completion(nil)
                }
            })
        }
    } else {
        // We shouldn't get here
        completion(nil)
    }
}

Answer 3

It is a very simple thing...

    PHFetchOptions *userAlbumsOptions = [PHFetchOptions new];
    userAlbumsOptions.predicate = [NSPredicate predicateWithFormat:@"estimatedAssetCount > 0"];

    PHFetchResult *userAlbums = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAny options:userAlbumsOptions];

    [userAlbums enumerateObjectsUsingBlock:^(PHAssetCollection *collection, NSUInteger idx, BOOL *stop) {
    NSLog(@"album title %@", collection.localizedTitle);
    PHFetchResult *assetsFetchResult = [PHAsset fetchAssetsInAssetCollection:collection options:nil];
    PHAsset *asset = [assetsFetchResult objectAtIndex:0];
    NSInteger retinaMultiplier = [UIScreen mainScreen].scale;
    CGSize retinaSquare = CGSizeMake(80 * retinaMultiplier, 80 * retinaMultiplier);

    [[SDWebImageManager sharedManager] downloadImageWithURL:[NSURL URLWithString:asset.localIdentifier] options:SDWebImageProgressiveDownload targetLocalAssetSize:retinaSquare progress:^(NSInteger receivedSize, NSInteger expectedSize) {

    } completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
        if (image) {
            albumCoverImg.image = image;
        }
    }];
}];

and if you have not updated SDWebImage classed then load image as a normal way.