NSTable loses focus after present:error

I have an NSTableView that lists tags that are stored using Core Data. The default value for a tag is 'untitled' and I need each tag to be unique, so I have a validation routine that traps empty and non-unique values and that works fine. I don't want the user to be able to store the 'untitled' value for a tag, so I am observing the NSControlTextDidEndEditingNotification, which calls the following code:

- (void)textEndedEditing:(NSNotification 开发者_运维技巧*)note {
  NSString *enteredName = [[[note userInfo] valueForKey:@"NSFieldEditor"] string];
  if ([enteredName isEqualToString:defaultTagName]) {
    NSString *dString = [NSString stringWithFormat:@"Rejected - Name cannot be default value of '%@'", defaultTagName];
    NSString *errDescription = NSLocalizedStringFromTable( dString, @"Tag", @"validation: default name error");
    NSString *errRecoverySuggestion = NSLocalizedStringFromTable(@"Make sure you enter a unique value for the new tag.", @"Tag", @"validation: default name error suggestion");
    int errCode = TAG_NAME_DEFAULT_VALUE_ERROR_CODE;

    NSArray *objArray = [NSArray arrayWithObjects:errDescription, errRecoverySuggestion, nil];
    NSArray *keyArray = [NSArray arrayWithObjects:NSLocalizedDescriptionKey, NSLocalizedRecoverySuggestionErrorKey, nil];
    NSDictionary *eDict = [NSDictionary dictionaryWithObjects:objArray forKeys:keyArray];
    NSError *error = [[NSError alloc] initWithDomain:TAG_ERROR_DOMAIN code:errCode userInfo:eDict];

    NSBeep();
    [preferencesWindowsController presentError:error];

    unsigned long index = [self rowWithDefaultTag];
    [self selectRowIndexes:[NSIndexSet indexSetWithIndex:index] byExtendingSelection:NO];
    // [self editColumn:0 row:index withEvent:nil select:YES];
  }
}

- (unsigned long)rowWithDefaultTag {
  __block unsigned long returnInt;
  [managedTags enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    if ([[obj valueForKey:@"name"] isEqualToString:defaultTagName]) {
    returnInt = idx;
    *stop = YES;
    }
  }];
  return returnInt;
}

With the 'editColumn' line commented out, the code works, so if the user accepts the default tag name without editing it, the error is built, displayed and the process finishes by leaving the appropriate row in the table highlighted.

However, I would like to take it that step further and place the user in edit mode. When I uncomment the 'editColumn' line, the behaviour is not at all what I expected - the tableView loses its blue focus box and the row that respresents the new tag is blank. If I click on the tableView, the row becomes visible. I've spent a lot of time on this and have got nowhere, so some help with this would be very much appreciated.

(Note: I tried using textDidEndEditing, which also didn't behave as I expected, but that is a separate issue!)

Answering my own question. Doh!

I already had a method which I used to put the user in edit mode when they clicked the button to add a new tag:

- (void)objectAdded:(NSNotification *)note {
  if ([[note object] isEqual:self]) {    
    [self editColumn:0 row:[self rowWithDefaultTag] withEvent:nil select:YES];
  }
}

Creating a notification to call this solves the problem and places the user in edit mode correctly. The important thing is not to try to do this on the existing runloop; so sending the notification as follows postpones delivery until a later runloop:

// OBJECTADDED is a previously defined constant.
NSNotification * note = [NSNotification notificationWithName:OBJECTADDED  object:self];
[[NSNotificationQueue defaultQueue] enqueueNotification: note postingStyle: NSPostWhenIdle];

Problem solved. I wasted a lot of time trying to solve this - a classic example of getting too involved in the code and not looking at what I'm trying to do. I've forgotten where I first saw this posted - whoever you are, thank you!