CODEWITHSUNDEEP
iosuitableviewcore-datansfetchedresultscontroller
trapper
trapper

Reputation: 11993

Multiple NSFetchedResultsController's with one UITableView?

Visually I have a UITableView with a UISegmentedControl to allow 'mode' selection which will change the table's sort order .

Using NSFetchedResultsController's I am thinking I should keep a separate controller for each different sort configuration then swap between which one is being displayed based on the currently selected 'mode'.

However I can see this will get tricky with 4 different NSFetchedResultsController all sending delegate messages to update the UITableView. To deal with this I am planning to use a switch() block in each of the relevant methods to ignore all but the currently 'active' NSFetchedResultsController.

Does this sound like the right approach or am I missing something obvious here?

-I can see potential for disaster if the user changes the 'mode' just as an update comes through (ie between controllerWillChangeContent: and controllerDidChangeContent:)

Upvotes: 2

Views: 446

Answers (2)

melsam
melsam

Reputation: 4977

I've used a segment control to change sorting/grouping in several Core Data apps. In all of them, I've always just used a single NSFetchedResultsController, and re-queried the database when the segment changes.

As you correctly realized, it is a far simpler implementation that way, fewer chances of unexpected errors, and is also more scalable. E.g. what if I decide to add a new sorting/grouping segment based on customer feedback? How many NSFetchedResultsController's are you going to keep adding? At some point (5 or 6) it just becomes ridiculous.

Also graver's comment above that you could set all of their delegates, except the "active one" to nil won't scale (you would have to modify many lines of code to make all the other delegates nil, which will make maintaining the code hard.

So my suggestion is to go with the simpler implementation, which is a single NSFetchedResultsController, and recreate it every time the segment changes. If you're interested in caching, you could use a separate cache name for each segment. A unique cache name can be generated for each segment by concatenating something like: 

[NSString stringWithFormat:@"Cache_%d", segment_index]

Upvotes: 2

graver
graver

Reputation: 15213

Isn't it more logical when the segmented control's selected index is changed, to change the sort descriptors and performFetch?

self.fetchedResultsController.fetchRequest.sortDescriptors = [NSArray ... ];

Upvotes: 2

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