一对多关系核心数据：抓取prepareForSegue：

Question

在过去的几个小时里，我一直在撕掉我的头发，试图找出为什么这不起作用。我在Core Data中有一对多的关系，并试图正确地将值传递给细节segue。

下面是数据模型（该属性是二进制数据类型）：

如果我取的configureCell数据：方法，它给我的预期值：

- (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数时，它会崩溃，并出现无法识别的选择器错误。详细信息视图控制器的

- (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：

- (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]; 
} 

我觉得我在这里缺少一些明显的阶梯，为什么它不工作。我可以得到任何帮助吗？

Answer 1

你没有设置细节everythingGroup：

NSArray *urls = [NSKeyedUnarchiver unarchiveObjectWithData:self.everything.urls.urls]; 
details.everythingGroup = [urls objectAtIndex:indexPath.section]; 

正如我在URLs.urls看到的是归档到一个NSData字典的数组。所以details.everythingGroup现在是一本字典，但你访问它这样：

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

这是正常的，它的崩溃在这里。 在您访问它时，看起来像details.everythingGroup应该是Everything。

Answer 2

您的self.everythinggrpup是一个NSDictionary，因此不会响应选择器“urls”。有些人，你正在分配一个NSDictionary，而不是一个Everything对象self.everythinggroup。所以你不需要那样做，或者把所有的东西都从这个字典中提取出来，然后再问它是否是url。取决于你如何设置。