【发布时间】：2011-11-04 00:13:03
【问题描述】：
好的，我在 Core Data 方面做得越来越好，但我还有很长的路要走。这就是我在加载视图时填充 fetchedResultsController 的方式：
- (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:@"Visit" 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:@"date" ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects: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:@"Queue"];
aFetchedResultsController.delegate = self;
self.fetchedResultsController = aFetchedResultsController;
NSPredicate *predicate =[NSPredicate predicateWithFormat:@"(isActive == YES)"];
[fetchedResultsController.fetchRequest setPredicate:predicate];
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error])
{
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return __fetchedResultsController;
}
这很好用。我将 fetchedResultsController 连接到我的 tableView 并且我有 5 个托管对象正在显示。我遇到的问题是当我需要对其中一个托管对象进行更改时。
正如您在谓词中看到的，我指定我只想要具有isActive == YES 的托管对象。我需要将托管对象的 isActive 状态更改为 NO，然后将其从 fetchedResultsController 中删除，最终从 tableView 中删除。
这是我的尝试：
-(void) seatedButton{
Visit * vis = [self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:reloadIndex inSection:0]];
vis.isActive = [NSNumber numberWithBool:NO];
NSError *error = nil;
if (![self.managedObjectContext save:&error])
{
/*
Replace this implementation with code to handle the error appropriately.
abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
[tableView reloadData];
}
这似乎可行，但它没有。当 tableView 重新加载时，有 5 个对象符合谓词的要求，而它应该只有 4 个！
我在这里做错了什么？我需要做什么来更新 fetchedResultsController？谢谢！
【问题讨论】：
标签： iphone objective-c core-data nspredicate nsfetchedresultscontroller