+ Model Archiving
+ topSongs Cache date
work around encodeObject(items.bridgeToObjectiveC(),..)
impl load topSongs data from cache
+ UIActivityIndicatorView
NSOperationQueue.mainQueue().addOperationWithBlock
extension array containsObject
+ property: publicationDate
sort RSSItem order by date descending
impl copyWithZone
+ CoreData
marked item as read and had been read
set checkmark for cell
fix: NSPredicate.format string