Swift editing related Core Data objects with NSFetchedResultsController across views / how do I format and use NSPredicate with a block?

Question

I have a question regarding editing/deleting Core Data objects in a UIListView that are related to another object.

To simplify the problem, let's say I have a list view of Family objects. Tapping on a Family name opens a list view of FamilyMember objects for the chosen Family object. I have a one to many relationship between Family and FamilyMember set up in Core Data.

I perform an NSFetchRequest to grab the list of all 'Family' objects in my initial table view controller and put them into an NSFetchedResultsController . When a family in the list is tapped, that 'Family' object is passed into the FamilyMembersViewController with prepareForSegue .

The issue I'm facing is that since I passed in a 'Family' object directly from the initial view controller to FamilyMembersViewController , I never had to create a FetchRequest or a NSFetchedResultsController in FamilyMembersViewController . Therefore, some editing functions that worked great on the initial view now don't work in the FamilyMembersViewController .

How do I take advantage of NSFetchedResultsController functions (such as the following) in a view that doesn't have a NSFetchedResultsController ? Do I need to re-query Core Data, limiting the results to a specific 'Family" object? It seems like a waste since I already have the object available in my view.

Am I approaching this functionality incorrectly? I guess I'm just hoping to have the functions be similar from one view controller to the next.

I've tried making a new array called 'familyMembers' and a corresponding NSFetchedResultsController within my FamilyMembersViewController and predicated it with this:

var predicate = NSPredicate(format: "family == %@", "\(self.family)")

where self.family is the 'Family' object passed from the initialView . But in this case, for some reason the "self.family" part just returns an empty string, when really it should return the Family object. Even if it did return the Family object, it doesn't seem like passing that into the predicate would help anything, since the predicate seems to match only strings. I can't quite figure out how to format a Predicate with a block statement.

Any help would be much appreciated! Thank you for reading.

func controllerWillChangeContent(controller: NSFetchedResultsController!) {
    tableView.beginUpdates()
}

func controller(controller: NSFetchedResultsController!, didChangeObject anObject: AnyObject!, atIndexPath indexPath: NSIndexPath!, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath!) {
    switch type {
    case .Insert:
        tableView.insertRowsAtIndexPaths([newIndexPath], withRowAnimation: .Fade)
    case .Delete:
        tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    case .Update:
        tableView.reloadRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    default:
        tableView.reloadData()
    }
    families = controller.fetchedObjects as [Family]
}

func controllerDidChangeContent(controller: NSFetchedResultsController!) {
    tableView.endUpdates()
}

Answer 1

尽管谓词参数不必是字符串，但您的做法正确无误-您可以传递family对象本身：

var predicate = NSPredicate(format: "family == %@", self.family)