Question

www.un.org/chinese/ecosoc

我有一个项目:

core data (using NSFetchedResultsController)
displaying the data in a table view (UITableView)

www.un.org/spanish/ecosoc 我想做的是:。

When a user adds a record, I want to scroll to the newly added record.

www.un.org/spanish/ecosoc 我做了些什么?

When a new record is added, Inside the NSFetchedResultsControllerDelegate method, I store the index path in a property lastAddedIndexPath when the type is insert / update / move
After invoking save, I scroll to the "lastAddedIndexPath"

<>Code>(NSFettorResultsControllerDelegate)

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{       
    if (!self.suspendAutomaticTrackingOfChangesInManagedObjectContext)
    {
        switch(type)
        {
            case NSFetchedResultsChangeInsert:
                [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
                NSLog(@"going to store insert - scroll");
                self.lastAddedIndexPath = newIndexPath;
                break;

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

            case NSFetchedResultsChangeUpdate:
                [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                NSLog(@"going to store update - scroll");
                self.lastAddedIndexPath = newIndexPath;
                break;

            case NSFetchedResultsChangeMove:
                [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
                NSLog(@"going to store move - scroll");
                self.lastAddedIndexPath = newIndexPath;
                break;
        }
    }
}

www.un.org/spanish/ecosoc 滚动守则

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    if (self.beganUpdates) //already [self.tableView beginUpdates] invoked
    {
        [self scrollToLastAddedIndexPath];  //contains the logic to scroll
        [self.tableView endUpdates];   
    }
}

<><>Problem>

I think the record is added to the table view asynchronously in a different thread.
so even after saving the database, when I scroll to the lastAddedIndexPath the record in the table doesn t exist yet.

<<>问题>

How would I be able to scroll to the newly added record path after the record has been added to the table view ?
Should I use notifications to know when the database is saved ?
Is there any other alternate approach ?

Answer 1

Your scrolling has to happen after [self.tableView endUpdates] since the new row is not added to the table until that point. So switch the two statements around:

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller 
{ 
    if (self.beganUpdates) //already [self.tableView beginUpdates] invoked 
    { 
        [self.tableView endUpdates]; 
        [self scrollToLastAddedIndexPath];  //contains the logic to scroll 

    } 
}

Answer 2

您应:

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {

或者,在添加新记录时,你可以使用KVO通知。

Answer 3

在我的设想中,需要在表上显示最后增加的物体,这样就采用一种不同的方法,即使用NSSortDescriptor对阵列进行分类,然后每增加一次重新上载表格,以补充/取代任何记录。 ......

NSSortDescriptor * sortDescriptor = [[[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO]autorelease];
NSArray * sortDescriptorArray = [[[NSArray alloc] initWithObjects:sortDescriptor,nil]autorelease];

self.commitsList =  [[self.listItem.itemCommit allObjects] sortedArrayUsingDescriptors:sortDescriptorArray];

[tblView reloadData];

And then you can use any key related to your data in initWithKey and sort your array to resolve this. And in CellForRowIndex method of table view you can use this array to populate tableview.

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