How to use the first character as a section name

cocoa-touch, core-data, iphone, objective-c, uitableview

Solution

You should just pass "name" as the sectionNameKeyPath. See this answer to the question "Core Data backed UITableView with indexing".

UPDATE That solution only works if you only care about having the fast index title scroller. In that case, you would NOT display the section headers. See below for sample code.

Otherwise, I agree with refulgentis that a transient property is the best solution. Also, when creating the NSFetchedResultsController, the sectionNameKeyPath has this limitation:

If this key path is not the same as that specified by the first sort descriptor in fetchRequest, they must generate the same relative orderings. For example, the first sort descriptor in fetchRequest might specify the key for a persistent property; sectionNameKeyPath might specify a key for a transient property derived from the persistent property.

Boilerplate UITableViewDataSource implementations using NSFetchedResultsController:

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return [[fetchedResultsController sections] count];
}

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

- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index {
    return [fetchedResultsController sectionForSectionIndexTitle:title atIndex:index];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo numberOfObjects];
}

// Don't implement this since each "name" is its own section:
//- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
//    id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
//    return [sectionInfo name];
//}

UPDATE 2

For the new 'uppercaseFirstLetterOfName' transient property, add a new string attribute to the applicable entity in the model and check the "transient" box.

There are a few ways to implement the getter. If you are generating/creating subclasses, then you can add it in the subclass's implementation (.m) file.

Otherwise, you can create a category on NSManagedObject (I put this right at the top of my view controller's implementation file, but you can split it between a proper header and implementation file of its own):

@interface NSManagedObject (FirstLetter)
- (NSString *)uppercaseFirstLetterOfName;
@end

@implementation NSManagedObject (FirstLetter)
- (NSString *)uppercaseFirstLetterOfName {
    [self willAccessValueForKey:@"uppercaseFirstLetterOfName"];
    NSString *aString = [[self valueForKey:@"name"] uppercaseString];

    // support UTF-16:
    NSString *stringToReturn = [aString substringWithRange:[aString rangeOfComposedCharacterSequenceAtIndex:0]];

    // OR no UTF-16 support:
    //NSString *stringToReturn = [aString substringToIndex:1];

    [self didAccessValueForKey:@"uppercaseFirstLetterOfName"];
    return stringToReturn;
}
@end

Also, in this version, don't forget to pass 'uppercaseFirstLetterOfName' as the sectionNameKeyPath:

NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext
sectionNameKeyPath:@"uppercaseFirstLetterOfName" // this key defines the sections
cacheName:@"Root"];

And, to uncomment `tableView:titleForHeaderInSection:` in the UITableViewDataSource implementation:

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    id <NSFetchedResultsSectionInfo> sectionInfo = [[fetchedResultsController sections] objectAtIndex:section];
    return [sectionInfo name];
}

Problem

Original source

Related problems

• Core Data backed UITableView with indexing
• NSFetchedResultsController v.s. UILocalizedIndexedCollation