NSFetchedResultsController objectAtIndex、objectAtIndexPath、indexPathForObject 不一致

Question

我有一个包含单个部分的提取结果。我可以使用 [[fetchedResultsController fetchedObjects] objectAtIndex:index] 访问所有对象的对象。但是，当我像这样使用 objectAtIndexPath 时，它会失败： [fetchedResultsController objectAtIndexpath:indexPath]

将一行（对于其中一个 SearchResult 对象）插入到相应的表中后发生错误。该对象似乎已正确插入到新表中。在我目视确认这一点后，我选择其中一行，然后乐趣就开始了。

这是发生错误的代码：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    SearchResult *event;
    NSLog(@"Number of sections in fetchedResultsController: %d", [[fetchedResultsController sections] count]);
    for (NSUInteger i=0; i<[[fetchedResultsController fetchedObjects] count]; i++) {
        event = (SearchResult*)[[fetchedResultsController fetchedObjects] objectAtIndex:i];
        NSLog(@"object at index[%d]: %@", i, event.title );
        NSLog(@"indexPath for object at index[%d]:%@", i, [fetchedResultsController indexPathForObject:event]);
    }

    NSLog(@"indexPath passed to method: %@", indexPath);

    SearchResult *result = [fetchedResultsController objectAtIndexPath:indexPath];  // *** here is where the error occurs ***

    [viewDelegate getDetails:result];
}

我在最后一行出现故障。日志如下所示：

Number of sections in fetchedResultsController: 1
object at index[0]: Cirles
indexPath for object at index[0]:(null)
object at index[1]: Begin
indexPath for object at index[1]:(null)
object at index[2]: Copy
indexPath for object at index[2]:(null)
object at index[3]: Unbound
indexPath for object at index[3]:(null)
indexPath passed to method: <NSIndexPath 0x64ddea0> 2 indexes [0, 2]

执行 NSLog 语句后，我使用 [fetchedResultsController objectAtIndexPath:indexPath] 在最后一行收到异常。其他索引值也会发生这种情况，但它们看起来总是有效的。

*** 由于未捕获的异常“NSInternalInconsistencyException”而终止应用程序，原因：“索引 0 部分中索引 2 处没有对象”

因此，总而言之，似乎存在正确数量的获取对象，有一个部分（0），我可以通过一种方法访问每个部分，但不能通过另一种方法访问。 indexPathForObject: 始终返回 (null)。

这是一个错误还是我误解了什么？

---

更新

这是实现 NSFetchedResultsControllerDelegate 协议方法的代码。

- (void) controllerWillChangeContent:(NSFetchedResultsController *)controller {
    NSLog(@"Favorites controllerWillChangeContent");
    [self.tableView beginUpdates];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller 
{
    NSLog(@"Favorites Table controllerDidChangeContent");
    [self.tableView endUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller 
   didChangeObject:(id)anObject 
       atIndexPath:(NSIndexPath *)indexPath 
     forChangeType:(NSFetchedResultsChangeType)type 
      newIndexPath:(NSIndexPath *)newIndexPath {

    NSLog(@"Favorites Changed Object");

    switch (type) {
        case NSFetchedResultsChangeInsert:
            NSLog(@"--- Favorite was inserted");
            if ([[self.fetchedResultsController fetchedObjects] count] == 1) {
                // configure first cell to replace the empty list indicator by first deleting the "empty" row
                [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationNone];
            }

            [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationNone];

            break;

        case NSFetchedResultsChangeDelete:
            NSLog(@"--- Favorite was deleted");

            [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationNone];
            if ([[self.fetchedResultsController fetchedObjects] count] == 0) {
                // configure first cell to show that we have an empty list
                [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationNone];
            }

            break;

        case NSFetchedResultsChangeMove:
            NSLog(@"--- Favorite was moved");

            break;

        case NSFetchedResultsChangeUpdate:
            NSLog(@"--- Favorite was updated");
            [self configureCell:(ResultCell*)[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];

            break;

        default:
            break;
    }

}

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo 
           atIndex:(NSUInteger)sectionIndex 
     forChangeType:(NSFetchedResultsChangeType)type {

    switch (type) {
        case NSFetchedResultsChangeInsert:
            NSLog(@"Favorites Section Added");

            break;

        case NSFetchedResultsChangeDelete:
            NSLog(@"Favorites Section Deleted");

            break;

        default:
            break;
    }

}

---

更新 2

我不知道这是否重要，但 tableView 是用这一行初始化的：

    tableView = [[UITableView alloc] initWithFrame:CGRectMake(...) style:UITableViewStyleGrouped];

---

更新 3

当我按如下方式更改有问题的行时，它工作正常。但我宁愿保持索引与表相同。

//SearchResult *result = [self.fetchedResultsController objectAtIndexPath:indexPath];
SearchResult *result = [[self.fetchedResultsController fetchedObjects] objectAtIndex:[indexPath indexAtPosition:1]]

Answer 1

我现在也有同样的问题。

对我来说，它有助于使用 cacheName: nil 初始化 NSFetchedResultsController。