New to Core Data for iphone

Question

I am new to the iphone platform and am creating an app that retrievals a rss feed and displays it in a UITableView. I have gotten this working perfectly (or rather, the way I wanted). What I was thinking was I would store the current feed items on the phone so that it would initally load the old items it has stored while it got the new feed, then parse the new feed and add the new items and refresh the TableView. I was going to use Core Data to store it the old feed items because it would be a good way of learning Core Data and it would be an appropriate use of Core Data. However, I am having a difficult time learning how to use Core Data and connecting it with the Table/Array.

I have already googled and looked on stackoverflow for tutorials but have yet to find anything that explains it in a way I really understand. Any explanation of the overall steps that it takes to add Core Data to an existing app would be greatly appreciated. Full-blown detail are not necessary (but would also be useful). I'm just not very experienced with SQL or storing of data in such a manner and am having trouble wrapping my head around how the whole concept of Core Data works and how it connects to everything.

Also, any better method of doing what I'm trying to accomplish would also be appreciated.

Answer 1

If you are using CoreData to populate a UITableView you really want to use NSFetchedResultsController as opposed to trying to populate and sync array yourself. The documentation for NSFetchedResultsController includes links to several CoreData tutorials, including onces that populate table views.

Answer 2

There exist Xcode templates for Core Data-based applications; these are a great start to getting Core Data off the ground. However, it sounds like you want to integrate Core Data into your existing app, so you'll need to...

• Add three main Core Data objects: the managed object context (MOC), the managed object model (MOM), and the persistent store coordinator (PSC). These need to be accessible wherever you want Core Data available, so either in your app delegate or, more preferably, in the controller or data source for your table view.
• Create a MOM in Xcode. This will be a file of type .xcdatamodel, and it's an object graph that defines all the Core Data entities you want in your app.
• Use NSFetchedResultsController (as suggested by Louis Gerbarg) to get data out of Core Data and display it into your table view.
• Add code in your existing RSS-fetching-and-parsing routines to store new Core Data objects back into the store, when appropriate.

A good way to start is just to create a new Core Data application and play around with it a bit; you can also look at Apple's fantastic resources on the subject, like the Core Data Programming Guide and the sample apps Recipes and Locations. (Developer registration may be required.)

One last thing to note is that for the most part, a lot of the Core Data code you need to add can be ripped straight out of one of the Xcode template apps and pasted into your program (this holds especially true for the accessors for the three Core Data objects you need). Be careful not to use code you don't understand, though.

Answer 3

NSFetchedResultsController is still a bit buggy and requires fragile workarounds. I would start with the simpler iPhone Core Data "location" tutorial before moving on to the Books tutorial.

Answer 4

Also, any better method of doing what I'm trying to accomplish would also be appreciate

yes, it sounds like Core Data might be overkill for your application. Assuming your feed items are stored in a collection object you can easily use OSX's built in serializaition.

Answer 5

Been noted in other Stack-Overflow posts, but I can highly recommend the Prag Prog book "Core Data: Apple's API for Persisting Data on Mac OS X" - most is also relevant to iPhone Core Data apps; there is a whole chapter on creating an iPhone app too.

http://pragprog.com/titles/mzcd/core-data