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. :)