Question

我的应用程序中存在一个奇怪的问题。

我实例化一个NSFetchedResultsController来填充我的数组。

它以这种方式声明（作为@propoerty (nonatomic, retain)）

- (NSFetchedResultsController *)fetchedContactsController {
    if (self->fetchedContactsController != nil) return self->fetchedContactsController;

    // Create the fetch request
    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];

    // I want every contact...
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Contact" inManagedObjectContext:self->managedObjectContext];
    [fetchRequest setEntity:entity];

    // ... whose are not associated with my order item
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT (%@ IN items)", self.orderItem];
    [fetchRequest setPredicate:predicate];

    // Edit the section name key path and cache name if appropriate
    self.fetchedContactsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self->managedObjectContext sectionNameKeyPath:nil cacheName:nil];

    [aFetchedResultsController release];
    [firstnameSortDescriptor release];
    [lastnameSortDescriptor release];
    [sortDescriptors release];
    [fetchRequest release];

    // Execute the fetch request
    [self->fetchedContactsController performFetch:nil];
    return self->fetchedContactsController;
}

当然，contacts.items存在。

当我的应用程序进入后台时，再次前景，如果我再做一次

NSLog(@"before >>> %d", [[fetchedContactsController fetchedObjects]count]); // >>> 3
[self->fetchedContactsController performFetch:nil];
[tableView reloadData];
NSLog(@"after >>> %d", [[fetchedContactsController fetchedObjects]count]); // >>> 0

我阵列中的每一行都消失了！

编辑：

如果我评论这些行：

    // ... whose are not associated with my order item
    //NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT (%@ IN items)", self.orderItem];
    //[fetchRequest setPredicate:predicate];

问题不再发生了！但那不是我想要的......

Answer 1

好的，我找到了。 Thanks to this question，我替换了这一行：

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT (%@ IN items)", self.orderItem];

通过

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"NOT SELF IN %@", self.orderItem.recipients];

有趣的是，你问一个问题的事实会让你走上解决的道路。

NSFetchedResultsController在输入背景后丢失了他的行

1 个答案: