How to "sync" UI with Core Data?

Question

I would like to know what is the usual approach for syncing UI with Core Data, for example when you display data stored by Core Data in a table view, and you want to show additional info about an object when the user taps its cell in the table view, how would you link the table view cell to a specific object in Core Data ? I have seen many people not recommending to use IDs since Core Data wasn't designed in this way, but then what to use if we are not using an ID ? I would have wanted to do something like : "OK, the selected cell has this ID, let's go in Core Data fetch the object with the same ID" But if I'm not doing this, how can I do ?

Same question for other cases where you need this kind of link... in my case, I need a link between pins on a map and Core Data objects, so that I display additional info when the pin is tapped, a little bit like in Apple Maps for example...

What should I do ?

Thank you.

score 1 · Accepted Answer · answered Jul 18 '15 at 10:35

1

You can do that by using NSFetchedResultsController - you can subclass your UITableViewController from CoreDataTableViewController (.h .m) and the only method you need to override would be cellForRowAtIndexPath:. Then can access objects directly like this:

MyCustomObject *obj = [self.fetchedResultsController objectAtIndexPath:indexPath];

answered Jul 18 '15 at 10:35

Islam

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(when I'm not using a table view ?) – Pop Flamingo Jul 18 '15 at 10:36
Then you'll just simply use a `ViewController` to manage your data with `existingObjectWithID:error:` or `objectWithID:` ([good explanation](http://stackoverflow.com/a/5035310/2177402)) – Islam Jul 18 '15 at 10:44

score 0 · Answer 2 · answered Jul 18 '15 at 16:00

For your second question, when you are not using a table view there are two options. One you can fetch the object (assuming you are at the very top of the stack) or two, far more common, you have the NSManagedObject instance passed into you using simple dependency injection during the storyboard segue.

Any view that is below/after a table view should never need to fetch or call something like -objectWithID: as the object is already in memory and the controller that is giving you the ID already has the object. Just pass the object around like any other language.

How to "sync" UI with Core Data?

2 Answers2