一对多关系核心数据:在prepareForSegue中获取:
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【中文标题】一对多关系核心数据:在prepareForSegue中获取:【英文标题】:One-to-many relationship Core Data : fetching in prepareForSegue: 【发布时间】:2013-11-03 07:48:52 【问题描述】:在过去的几个小时里,我一直在扯头发,试图弄清楚为什么这不起作用。我在 Core Data 中有一对多的关系,并且正在尝试将值正确传递给详细信息 segue。
下面是数据模型(属性为二进制数据类型):
如果我在 configureCell: 方法中获取数据,它会给我预期的值:
- (void)configureCell:(UITableViewCell *)cell atIndexPath(NSIndexPath *)indexPath
TBAppDelegate *delegate = (TBAppDelegate *)[[UIApplication sharedApplication] delegate];
managedObjectContext = [delegate managedObjectContext];
self.everything = [fetchedResultsController.fetchedObjects objectAtIndex:indexPath.section];
NSArray *arg = [NSKeyedUnarchiver unarchiveObjectWithData:self.everything.urls.urls];
NSLog (@"%@, [arg valueForKey:@"source"]); // this prints out a list of stored urls containing locations of jpeg images
我的 NSFetchedResultsController:
- (NSFetchedResultsController *)fetchedResultsController
TBAppDelegate *delegate = (TBAppDelegate *)[[UIApplication sharedApplication] delegate];
self.managedObjectContext = delegate.managedObjectContext;
NSFetchRequest *fetchRequest = nil;
fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = nil;
entity = [NSEntityDescription entityForName:@"Everything" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
[fetchRequest setFetchBatchSize:INFINITY];
NSSortDescriptor *albumDescriptor = nil;
albumDescriptor = [[NSSortDescriptor alloc] initWithKey:@"album_names" ascending:NO];
NSSortDescriptor *urlDescriptor = nil;
urlDescriptor = [[NSSortDescriptor alloc] initWithKey:@"urls.urls" ascending:NO];
NSArray *sortDescriptors = nil;
sortDescriptors = [[NSArray alloc] initWithObjects:albumDescriptor, urlDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSFetchedResultsController *frc = nil;
frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
[frc setDelegate:self];
[self setFetchedResultsController:frc];
return frc;
这是我的 prepareForSegue: 方法。这部分不起作用。当我尝试设置详细视图控制器的部分计数时,它会因无法识别的选择器错误而崩溃。
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
NSIndexPath *indexPath;
indexPath = [self.tableView indexPathForSelectedRow];
TBAppDelegate *delegate = (TBAppDelegate *)[[UIApplication sharedApplication] delegate];
managedObjectContext = [delegate managedObjectContext];
self.everything = [fetchedResultsController.fetchedObjects objectAtIndex:indexPath.section];
NSArray *data = [NSKeyedUnarchiver unarchiveObjectWithData:self.everything.album_names];
NSArray *urls = [NSKeyedUnarchiver unarchiveObjectWithData:self.everything.urls.urls];
TBEverythingDetailViewController *details = segue.destinationViewController;
details.everything = [[data objectAtIndex:indexPath.section]valueForKey:@"name"];
self.urls.urls = [fetchedResultsController.fetchedObjects objectAtIndex:indexPath.section];
details.everythingGroup = [urls objectAtIndex:indexPath.section];
部分细节视图控制器:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
// This is where the actual crash happens. It complains about [_NSDictionaryM urls:] unrecognized selector sent to instance
NSArray *count = [NSKeyedUnarchiver unarchiveObjectWithData:self.everythingGroup.urls.urls];
return [count count];
我觉得我在这里遗漏了一些明显的步骤,说明它为什么不起作用。我可以帮忙吗?
【问题讨论】:
你实际上是从 -fetchedResultsController 返回一个 NSFetchedResultsController 吗? 【参考方案1】:您确实将详细信息 EverythingGroup 设置为:
NSArray *urls = [NSKeyedUnarchiver unarchiveObjectWithData:self.everything.urls.urls];
details.everythingGroup = [urls objectAtIndex:indexPath.section];
正如我在 URLs.urls 中看到的,是一个归档到 NSData 中的字典数组。所以details.everythingGroup
现在是一本字典,但你正在访问它:
NSArray *count = [NSKeyedUnarchiver unarchiveObjectWithData:self.everythingGroup.urls.urls];
在这里崩溃是正常的。
当您访问它时,details.everythingGroup
应该是 Everything
。
【讨论】:
【参考方案2】:您的 self.everythinggrpup 是一个 NSDictionary,因此不会响应选择器“urls”。在某个地方,您将 NSDictionary 而不是 Everything 对象分配给 self.everythinggroup。所以你不需要这样做,或者从字典中取出所有对象,然后向它询问 url。取决于您是如何设置的。
【讨论】:
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