NSSortDescriptor issue

Question

I am making a contact book App where I am fetching names from AddressBook and stored them in Core data and displayed the names on a table using NSFetchedResultsControl

Answer 1

You could store an additional attribute sortName in the entity, which is fullName if the name starts with a letter, and fullName otherwise. is a fixed character which is "greater" than all letters. For example

NSString *special = @"\uE000";
if ("fullName starts with letter")
    sortName = fullName;
else
    sortName = [special stringByAppendingString:fullName];

Now you can sort according to sortName, and the section identifier would be "#" if sortName starts with the special character.

The disadvantage is that you have to store an additional attribute, the advantage is that you can continue to use a fetched results controller (which can use only persistent attributes for sorting).

UPDATE: It can actually be done a bit easier.

When you create a new entry, you set sectionIdentifier to the first character of the name if it is a letter, and to the special character otherwise:

NSString *special = @"\uE000";

if ([[NSCharacterSet letterCharacterSet] characterIsMember:[contact.contactName characterAtIndex:0]]) {
    contact.sectionIdentifier = [contact.contactName substringToIndex:1];
} else {
    contact.sectionIdentifier = special;
}

The fetched results controller uses sectionIdentifier for grouping and sorting the sections. Entries within each section are sorted by contactName:

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Contact"];
NSSortDescriptor *sort1 = [NSSortDescriptor sortDescriptorWithKey:@"sectionIdentifier"
             ascending:YES selector:@selector(localizedStandardCompare:)];
NSSortDescriptor *sort2 = [NSSortDescriptor sortDescriptorWithKey:@"contactName"
             ascending:YES selector:@selector(localizedStandardCompare:)];
[request setSortDescriptors:@[sort1, sort2]];
self.frc = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                   managedObjectContext:self.context
                     sectionNameKeyPath:@"sectionIdentifier"
                              cacheName:nil];

All non-letter entries are now grouped in the last section. The final step is to display the correct section header # for the last section:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    id  sectionInfo = [[self.frc sections] objectAtIndex:section];
    NSString *title = [sectionInfo name];
    if ([title isEqualToString:special])
        title = @"#";
    return title;
}