Ios 一对多关系核心数据：在prepareForSegue中获取：

在过去的几个小时里，我一直在绞尽脑汁，想弄明白为什么这样做行不通。我在核心数据中有一对多的关系，并且正在尝试将值正确地传递给细节序列

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，它将按预期提供值：

- (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;

}

- (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]; 
}

这是我的备考方式。这部分不起作用。当我尝试设置局部视图控制器的截面计数时，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];  
}

局部视图控制器的一部分：

- (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;

}

- (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来解释为什么它不起作用。我能帮忙吗

Your self.everythinggrpup是一个NSDictionary，因此不响应选择器“URL”。当你将NSDictionary而不是Everything对象分配给self.everythinggroup时。因此，您不需要这样做，或者从字典中取出everything对象，然后请求它提供URL。取决于您是如何设置的。

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URL.URL中看到的，URL是归档到NSData中的字典数组。所以

详细信息。everythingGroup

现在是一本字典，但您访问它的方式是：

NSArray*count=[NSKeyedUnarchiver unarchiveObjectWithData:self.everythingGroup.url.url]

它在这里坠毁是正常的。
当您访问它时，它看起来像是一个
详细信息。everythingGroup
应该是一个
Everything
您实际上是从-fetchedResultsController返回一个NSFetchedResultsController吗？