PHFetchOptions排序描述符不适用于[PHAssetCollection fetchAssetCollectionsWithType：..]

Question

尝试按字母顺序获取智能相册列表。我尝试对localizedTitle和title进行排序，但它们会产生相同的结果。

PHFetchOptions *options = [[PHFetchOptions alloc] init];
options.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"localizedTitle" ascending:YES]];

PHFetchResult *smartAlbums = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeSmartAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:options];

for (PHAssetCollection *collection in smartAlbums) {
    NSLog(@"PHAssetCollection: %@", collection.localizedTitle);
}

日志显示结果未按排序顺序返回：

2015-09-27 13:34:57.054 MyApp[2169:1043459] PHAssetCollection: Panoramas
2015-09-27 13:34:57.055 MyApp[2169:1043459] PHAssetCollection: All Photos
2015-09-27 13:34:57.055 MyApp[2169:1043459] PHAssetCollection: Hidden
2015-09-27 13:34:57.055 MyApp[2169:1043459] PHAssetCollection: Recently Deleted
2015-09-27 13:34:57.055 MyApp[2169:1043459] PHAssetCollection: Videos
2015-09-27 13:34:57.056 MyApp[2169:1043459] PHAssetCollection: Favorites
2015-09-27 13:34:57.056 MyApp[2169:1043459] PHAssetCollection: Slo-mo
2015-09-27 13:34:57.056 MyApp[2169:1043459] PHAssetCollection: Bursts
2015-09-27 13:34:57.056 MyApp[2169:1043459] PHAssetCollection: Time-lapse
2015-09-27 13:34:57.056 MyApp[2169:1043459] PHAssetCollection: Recently Added

我做错了什么？