NSFetchedResultsController创建节

Question

当使用NSFetchedResultsController为UITableViewController创建节头时，fetchedResultsController.sections的每个项目都有一个对象而不是每个节。

//Set up the request
NSManagedObjectContext *context = self.managedObjectContext;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

[fetchRequest setEntity:[NSEntityDescription entityForName:@"Person" 
                                    inManagedObjectContext:context]];

[fetchRequest setFetchBatchSize:20];

NSSortDescriptor *sortDescriptor = nil;
sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"firstName" 
                                             ascending:YES];
NSArray *sortDescriptors = nil;
sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[sortDescriptor release]; sortDescriptor = nil;

[fetchRequest setSortDescriptors:sortDescriptors];
[sortDescriptors release]; sortDescriptors = nil;

//setup fetch results controller
NSFetchedResultsController *controller = nil;
controller = [[NSFetchedResultsController alloc] 
              initWithFetchRequest:fetchRequest 
              managedObjectContext:context 
                sectionNameKeyPath:@"firstName" 
                         cacheName:@"PersonCache"];

__fetchedResultsController = controller;

[fetchRequest release]; fetchRequest = nil;

//IMPORTANT: Delete cache before changing predicate
[NSFetchedResultsController deleteCacheWithName:nil]; 
NSError *error = nil;
if (![controller performFetch:&error])
{
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
} else if ([[controller fetchedObjects] count] == 0){
    [self retrievePeoples];
}

NSLog(@"result count: %i", [[controller fetchedObjects] count]);
NSLog(@"section count: %i", [[controller sections] count]);
NSLog(@"sectionIndexTitles count: %i", [[controller sectionIndexTitles] count]);

返回：

result count: 18
section count: 18
sectionIndexTitles count: 13

部分计数和sectionIndexTitles计数不应该匹配吗？当调用numberOfSectionsInTableView：和tableView：numberOfRowsInSection：方法时，我应该能够查看fetchedResultsController.section以获取计数而无需任何其他排序。

如何正确设置NSFetchResultsController以使sections数组中的每个对象都是针对每个部分而不是针对所有对象？

Answer 1

Phillip Mills在另一个论坛上回答了这个问题。问题是我使用整个firstName来创建部分（而不仅仅是第一个字母）。修复是更新实体以在更新或更改时创建节标题。 Apple的DateSectionTitles有一个样本。