我正在研究我的第一个核心数据支持的应用程序,并且无法正确地设置NSFetchedResultsController。我有两个实体:NSFetchedResultsController/Parent-Child
/-----------\ /-----------\
| List | | ListItem |
| --------- | | --------- |
| listName | | itemName |
| --------- | | --------- |
| listItems |<---->> | list |
\ ---------/ \ ---------/
我有两个观点(分别来自UITableViewController
继承和各由NSFetchedResultsController
支持)。第一个视图是UITableView
,它显示List
项目的所有项目。当选中一行时,它将推动第二个视图。
我在视图控制器中有一个名为@property (strong, nonatomic) List *selectedList
的属性,我在选择List
之前将其分配,然后再按下视图。
我在设置时遇到的问题是,第二个视图仅显示ListItem
对象,其父对象为List
。我知道这属于NSFetchedResultsController
,但我不知道在哪里。
这里是我的代码:
- (NSFetchedResultsController *)fetchedResultsController
{
if (__fetchedResultsController != nil) {
return __fetchedResultsController;
}
// Set up the fetched results controller.
// Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"ListItem" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];
// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];
// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"timeStamp" ascending:NO];
NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Edit the section name key path and cache name if appropriate.
// nil for section name key path means "no sections".
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:@"Detail"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return __fetchedResultsController;
}
我是否需要添加某种排序描述符,或者其答案是否是别的东西?谢谢!