NSFetchRequest 控制器在 iOS 5 上工作，在 iOS 4.3 上崩溃

Question

我一直在尝试在一个至少需要 iOS 4.3 的项目中实现 Core Data。我让代码在 iOS 5 上运行没有任何问题，但是在 iOS 4.3 上尝试它时它会崩溃，原因如下：

Unresolved error Error Domain=NSCocoaErrorDomain Code=134060 "The operation couldn’t be completed. (Cocoa error 134060.)" UserInfo=0x4fb59b0 {reason=The fetched object at index 4 has an out of order section name 'Å. Objects must be sorted by section name'}, {
reason = "The fetched object at index 4 has an out of order section name '\U00c5. Objects must be sorted by section name'";

这是我的代码：

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

// Set up the fetched results controller.
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.

fetchRequest.entity = [NSEntityDescription entityForName:@"Exhibitor" 
                                  inManagedObjectContext:self.managedObjectContext];

// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" 
                                                               ascending:YES 
                                                                selector:@selector(caseInsensitiveCompare:)];

fetchRequest.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] 
                                                         initWithFetchRequest:fetchRequest
                                                         managedObjectContext:self.managedObjectContext 
                                                         sectionNameKeyPath:@"firstLetter" 
                                                         cacheName:nil];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;

NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
    /*
     Replace this implementation with code to handle the error appropriately.

     abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. 
     */
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

  return __fetchedResultsController;
}   

如果我在我的 sortDescriptor 中选择使用 caseInsensitivecompare: 而不是localizedCaseInsensitiveCompare: 它不会崩溃但顺序错误（因为我需要 Å Ä Ö 位于底部，而不是在 A 和 O 之后）。

建议？

更新： 好像当我在多任务栏中杀死我的应用程序然后重新启动它时，ÅÄÖ 的顺序是正确的（使用 caseInsensitiveCompare）。但只有在第一次重新启动之后。第一次启动还是出错...

Answer 1

您使用的是章节索引标题吗？这似乎是这个错误所指的。

只需添加：

-(NSString *)controller:(NSFetchedResultsController *)controller
             sectionIndexTitleForSectionName:(NSString *)sectionName {
   return sectionName;
}

到您的表格视图控制器。