CODEWITHSUNDEEP
iosuitableviewcore-datansfetchedresultscontroller
tierfour
tierfour

Reputation: 682

Indexed NSFetchedResultsController

How can I index a NSFetchedResultsController so that I can implement an A-Z index on a tableview.

I see in the initializer I can do sectionNameKeyPath but this just places unique objects in their own section.

Here is what I have for my NSFetchedResultsController 

    - (NSFetchedResultsController *)fetchedResultsController
{
    if (__fetchedResultsController != nil) {
        return __fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Customer" inManagedObjectContext:self.managedObjectContext];
    [fetchRequest setEntity:entity];

    [fetchRequest setFetchBatchSize:20];

    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];

    [fetchRequest setSortDescriptors:sortDescriptors];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:@"name" cacheName:@"Customer"];
    aFetchedResultsController.delegate = self;

    self.fetchedResultsController = aFetchedResultsController;

    return __fetchedResultsController;
}

Upvotes: 4

Views: 2667

Answers (4)

Kappe
Kappe

Reputation: 9505

correct version (ios 7.1 to 8.3):

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
  return [NSArray arrayWithObjects:@"A",@"B",@"C",@"D",@"E",@"F",@"G",@"H",@"I",@"J",@"K",@"L",@"M",@"N",@"O",@"P",@"Q",@"R",@"S",@"T",@"U",@"V",@"W",@"X",@"Y",@"Z",@"#",nil];
}

- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
{
    NSInteger section = 0;
    for (id <NSFetchedResultsSectionInfo> sectionInfo in [_fetchedResultsController sections])
    {
        if ([sectionInfo.indexTitle compare:title] >= 0)
        {
            break;
        }
        section++;
    }
    return section;
}

Upvotes: 0

sumizome
sumizome

Reputation: 712

@Harris' answer will show the whole alphabet on the side of the table. Unfortunately, if you then tap one of the letters that does actually have a corresponding section, you crash with something like:

Terminating app due to uncaught exception 'NSInternalInconsistencyException',
reason: 'Index title at 3 is not equal to 'K''

Upvotes: 1

Elijah
Elijah

Reputation: 8610

If you want to have the letters A-Z on the side (even though you don't have sections for every single letter) this will do it:

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
  return [NSArray arrayWithObjects:@"A",@"B",@"C",@"D",@"E",@"F",@"G",@"H",@"I",@"J",@"K",@"L",@"M",@"N",@"O",@"P",@"Q",@"R",@"S",@"T",@"U",@"V",@"W",@"X",@"Y",@"Z",@"#",nil];
}

- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
{
  index = 0;
  for(id sectionInfo in [_fetchedResultsController sections]){
    if ([[[sectionInfo name] uppercaseString] isEqualToString:title]){
      break;
    }
    index++;
  }
  if (index>=[_fetchedResultsController sections].count){
    return -1;
  }

  return [_fetchedResultsController sectionForSectionIndexTitle:title atIndex:index];
}

Upvotes: 0

Matthias Bauch
Matthias Bauch

Reputation: 90117

implement sectionIndexTitlesForTableView: like this:

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView {
    return [self.fetchedResultsController sectionIndexTitles];
}

this will give you those indexes on the right side of the tableView.

If you want your sections to have names like A, B, C, D etc. you have to implement a method that returns the first letter for your object.

something like this:

- (NSString *)firstLetter {
    [self willAccessValueForKey:@"firstLetter"];
    NSString *firstLetter = [[[self name] substringToIndex:1] uppercaseString];
    [self didAccessValueForKey:@"firstLetter"];
    return firstLetter;
}

This goes into the custom subClass of your coredata entity.

Then add a transient attribute named firstLetter to your core data entity and replace the sectionNameKeyPath in the NSFetchedResultsController init with firstLetter

Upvotes: 13

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