Friday, July 29, 2011

Core Data Tutorial: How To Use NSFetchedResultsController

So far, we're at exactly the same point we were using the SQLite3 method. However, we didn't have to write nearly as much code (notice the absence of a FailedBankDatabase class constructing raw SQL statements), and adding other functionality such as insert/delete operations would be much simpler.
However, there's one notable thing that we could add pretty easily with Core Data that could give us huge benefits to performance: use NSFetchedResultsController.
Right now we're loading all of the FailedBankInfo objects from the database into memory at once. That might be fine for this app, but the more data we have the slower this will be, and could have a detrimental impact to the user.
Ideally we'd like to load only a subset of the rows, based on what the user is currently looking at in the table view. Luckily, Apple has made this easy for us by providing a great utility class called NSFetchedResultsController.
So, start by opening up FailedBanksListViewController.h, removing out our old NSArray of failedBankInfos, and adding a new NSFetchedResultsController instead: