Question

在过去的几个小时里，我一直在撕扯我的头发，试图弄清楚为什么这样做不起作用。我在Core Data中有一对多的关系，我正在尝试将值正确地传递给细节segue。

下面是datamodel（属性是二进制数据类型）：

如果我在configureCell：方法中获取数据，它会为我提供预期的值：

- (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节数时，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];  
}

详细视图控制器的一部分：

- (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]; 
}

我觉得我在这里错过了一些明显的步骤，为什么它不起作用。我可以帮忙吗？

Answer 1

你的self.everythinggrpup是一个NSDictionary，因此不响应选择器“urls”。有些人你正在将一个NSDictionary而不是Everything对象分配给self.everythinggroup。所以你不需要那样做，或者从字典中获取所有对象，然后向它询问网址。取决于你如何设置它。

Answer 2

您确实将所有详细信息设置为：

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

正如我在URLs.urls中看到的那样，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];

它在这里崩溃是正常的。当您访问它时，details.everythingGroup应该是Everything。

一对多关系核心数据：在prepareForSegue中获取：

2 个答案: