我的 iPhone (4.1.2) 应用程序有一个菜单,每个菜单项都指向一个由 NSManagedObject
子类填充的不同表格 View 。我为每个使用相同的 View Controller ,但不同的是提取请求的谓词,因此根据用户选择的菜单项显示不同的数据。很简单。
在我实际保存托管对象上下文之前一切正常。然而,在应用程序进入后台并重新进入前台后,事情变得很奇怪,因为我正在使用这个:
- (void)applicationDidEnterBackground:(UIApplication*)application {
NSError *error = nil;
if(managedObjectContext != nil)
if([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
我认为这是保存我的数据的合适时间。但是在这发生之后,在我调用提取结果 Controller 上的 performFetch:
之后,它的 fetchedObjects
是来自 PREVIOUS 提取请求的提取对象,而不是新对象。也就是说,如果我这样做:
// Choose menu item 1
[self.fetchedResultsController performFetch:nil]; // With fetch request 1
NSLog(@"%i objects were fetched", [[self.fetchedResultsController fetchedObjects] count]); // Items for fetch request 1
// Go back to menu, choose menu item 2 for new fetch request
[self.fetchedResultsController performFetch:nil]; // Fetch request 2
NSLog(@"%i objects were fetched", [[self.fetchedResultsController fetchedObjects] count]); // Items for Fetch request 2
// Hit home button, applicationDidEnterBackground: is called
// Relaunch
// Choose menu item 1
[self.fetchedResultsController performFetch:nil]; // With fetch request 1
NSLog(@"%i objects were fetched", [[self.fetchedResultsController fetchedObjects] count]); // Items for fetch request 2 - HUH?
所以问题在于在我的托管对象上下文中调用 save:
。如果我从不保存数据,获取请求永远不会像这样混淆,但是一旦我保存了,就好像旧的获取请求被保存了一样,即使 fetchedResultsController
本身只是在我的 View Controller 的 viewDidLoad
方法。
有人知道发生了什么事吗?
更新:更多代码。
- (void)viewDidLoad {
delegate = (MAAppDelegate *)[[UIApplication sharedApplication] delegate];
managedObjectContext = delegate.managedObjectContext;
[self.fetchedResultsController performFetch:nil];
NSUInteger count = [[self.fetchedResultsController fetchedObjects] count]; // Bug is detected here
// ...
}
- (NSFetchedResultsController *)fetchedResultsController {
if(_fetchedResultsController)
return _fetchedResultsController;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Tweet" inManagedObjectContext:managedObjectContext];
NSPredicate *predicate = nil;
if([self.navigationItem.title isEqualToString:@"Personal"])
predicate = [NSPredicate predicateWithFormat:@"account.username = %@ AND user.username = %@", delegate.currentAccount.username, delegate.currentAccount.username];
else if([self.navigationItem.title isEqualToString:@"Favorites"])
predicate = [NSPredicate predicateWithFormat:@"account.username = %@ AND favorited = YES", delegate.currentAccount.username];
else
predicate = [NSPredicate predicateWithFormat:@"account.username = %@", delegate.currentAccount.username];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:20];
[fetchRequest setPredicate:predicate];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"tweetID" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:managedObjectContext
sectionNameKeyPath:@"retrieved"
cacheName:@"Root"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
[aFetchedResultsController release];
[fetchRequest release];
[sortDescriptor release];
[sortDescriptors release];
return _fetchedResultsController;
}
最佳答案
您是否在每个 subview 中缓存,如果是,您是否为每个缓存使用了不同的名称?
关于iphone - 奇怪的核心数据错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4423135/