如何在tableView行选择时更新fetchedResultsController？

Ok, I am getting better at this Core Data stuff, but I've got a ways to go. This is how I am populating my fetchedResultsController when my view loads:

好的,我在这个核心数据方面做得越来越好,但我还有很长的路要走。这是我在视图加载时填充fetchedResultsController的方法:

- (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;
}

This works great. I have the fetchedResultsController hooked up to my tableView and I have 5 managed objects that are showing up. The problem I am running into is when I need to make a change to one of the managed objects.

这很好用。我有fetchedResultsController连接到我的tableView,我有5个托管对象出现。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。

As you can see in the predicate I am specifying that I only want managed objects that have isActive == YES. I need to change a managed object's isActive status to NO, and then remove it from the fetchedResultsController, and ultimately the tableView.

正如您在谓词中看到的那样,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,最后将其从tableView中删除。

Here is how I am trying to do that:

这是我试图这样做的方式:

-(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];

}

It appears that this would work, but it doesn't. When the tableView is reloaded, 5 objects come back as fitting the requirements of the predicate, when it should only be 4!

看来这会起作用,但事实并非如此。当重新加载tableView时,5个对象返回以符合谓词的要求,当它应该只有4时!

What am I doing wrong here? What do I need to do to update the fetchedResultsController? Thanks!

我在这做错了什么?我需要做些什么才能更新fetchedResultsController?谢谢!

2 个解决方案

#1

There are delegate methods to the fetchedResultsController you may want to use that should do this all for you automatically. Once you save the context, it update the table for you, so you won't have to call [tableView reloadData]

你可能想要使用的fetchedResultsController有委托方法,应该自动为你完成所有这些。保存上下文后,它会为您更新表,因此您不必调用[tableView reloadData]

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
    switch(type) {
        case NSFetchedResultsChangeInsert:
            [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    UITableView *tableView = self.tableView;

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [self.tableView endUpdates];
}

EDIT: If you do this, you will need to implement the following method:

编辑:如果这样做,您将需要实现以下方法:

- (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath {
    // configure cell;
}

#2

I'm pretty sure adding the following code into your seatedButton method, just before the line with [tableView reloadData] will fix the problem, but not sure according to the doc that it should be necessary.

我非常确定将以下代码添加到您的seatButton方法中,就在使用[tableView reloadData]行解决问题之前,但根据文档不确定它应该是必要的。

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();
}