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POIndexing results from an NSFetchedResultsController
 

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    <p>I'm having some issues with a mixed, indexed, searchable results set from an NSFetchedResults controller. I have it set up to store an indexed A-Z first initial for an entity, and then want it to display numeric first initials (i.e. # as the UILocalizedIndexCollation would do). </p> <p>I have already written the code that saves a "firstInitial" attribute of an Artist object as NSString @"#" if the full name started with a number, and I seem to have gotten the code half working in my UITableViewController with a customised sort descriptor. The problem is that it only works until I quit/relaunch the app. </p> <p>At this point, the # section from the fetched results appears at the top. It will stay there until I force a data change (add/remove a managed object) and then search for an entry, and clear the search (using a searchDisplayController). At this point the section re-ordering will kick in and the # section will be moved to the bottom...</p> <p>I'm obviously missing something/have been staring at the same code for too long. Alternatively, there's a much easier way of doing it which I'm not aware of/can't find on Google!</p> <p>Any help would be appreciated!</p> <p>Thanks</p> <p>Sean</p> <p>The relevant code from my UITableViewController is below.</p> <pre><code>- (void)viewDidLoad { // ---------------------------------- // Various other view set up things in here.... // ... // ... // ---------------------------------- NSError *error; if (![[self artistResultsController] performFetch:&amp;error]) { // Update to handle the error appropriately. NSLog(@"Failed to fetch artists: %@, %@", error, [error userInfo]); exit(-1); // Fail } } - (NSFetchedResultsController *)artistResultsController { if (_artistResultsController != nil) { return _artistResultsController; } NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Artist" inManagedObjectContext:_context]; [fetchRequest setEntity:entity]; NSSortDescriptor *initialSort = [[NSSortDescriptor alloc] initWithKey:@"firstInitial" ascending:YES comparator:^(id obj1, id obj2) { // Various number conditions for comparison - if it's a # initial, then it's a number if (![obj1 isEqualToString:@"#"] &amp;&amp; [obj2 isEqualToString:@"#"]) return NSOrderedAscending; else if ([obj1 isEqualToString:@"#"] &amp;&amp; ![obj2 isEqualToString:@"#"]) return NSOrderedDescending; if ([obj1 isEqualToString:@"#"] &amp;&amp; [obj2 isEqualToString:@"#"]) return NSOrderedSame; // Else it's a string - compare it by localized region return [obj1 localizedCaseInsensitiveCompare:obj2]; }]; NSSortDescriptor *nameSort = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; [fetchRequest setSortDescriptors:[NSArray arrayWithObjects:initialSort, nameSort, nil]]; [fetchRequest setFetchBatchSize:20]; NSFetchedResultsController *theFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:_context sectionNameKeyPath:@"firstInitial" cacheName:nil]; self.artistResultsController = theFetchedResultsController; _artistResultsController.delegate = self; [nameSort release]; [initialSort release]; [fetchRequest release]; [_artistResultsController release]; return _artistResultsController;} - (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section { if (tableView == self.searchDisplayController.searchResultsTableView) { return nil; } else { return [[[_artistResultsController sections] objectAtIndex:section] name]; } } - (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView { if (tableView == self.searchDisplayController.searchResultsTableView) { return nil; } else { return [[NSArray arrayWithObject:UITableViewIndexSearch] arrayByAddingObjectsFromArray: [[UILocalizedIndexedCollation currentCollation] sectionIndexTitles]]; } } - (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index { if (tableView == self.searchDisplayController.searchResultsTableView) { return 0; } else { if (title == UITableViewIndexSearch) { [tableView scrollRectToVisible:self.searchDisplayController.searchBar.frame animated:NO]; return -1; } else { for (int i = [[_artistResultsController sections] count] -1; i &gt;=0; i--) { NSComparisonResult cr = [title localizedCaseInsensitiveCompare: [[[_artistResultsController sections] objectAtIndex:i] indexTitle]]; if (cr == NSOrderedSame || cr == NSOrderedDescending) { return i; } } return 0; } } } </code></pre> <p>EDIT: Forgot to mention - my search filter is using a predicate on the fetchedResults controller, so this causes a new fetch request, like so</p> <pre><code>- (void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope { NSFetchRequest *aRequest = [_artistResultsController fetchRequest]; NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name BEGINSWITH[cd] %@", searchText]; // set predicate to the request [aRequest setPredicate:predicate]; // save changes NSError *error = nil; if (![_artistResultsController performFetch:&amp;error]) { NSLog(@"Failed to filter artists: %@, %@", error, [error userInfo]); abort(); } } </code></pre>
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    1. COWhat do you mean, "it only works until I quit/relaunch the app." What behavior did you expect with a sort descriptor?
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    2. COSince the data itself is in coreData, I'd expect it to run the comparator each time I instantiate the NSFetchedResultsController - which in this case, should be each time the view is loaded. Based on some NSLogging I've done, the comparator block doesn't get hit when the view first loads - even though breakpoints show that the sort descriptor is alloc'd on view load - this explains why it hasn't been sorted correctly. I guess the problem here is how do I force the fetched results controller to sort my data this way initially?
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      1. USSean Bedford
    3. COCheck for my extended answer: stackoverflow.com/a/15587961/1791090
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Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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