How can i detect new items in rss feed

I am making an app that will load stories from rss feed and store them locally 开发者_运维百科in Documents folder, so they would be available offline. My question is: How can i detect new items so i could update the existing stories list.

You would need to re-query the feeds. Either add a "Refresh" button which loads new data, or you can have a timer execute a reloading method every few minutes or whatever you require.