NSTreeController remove: does not call outlineViewSelectionDidChange: when removing the last child

After a hiatus from Cocoa development, I’ve recently been trying out some sample projects. And, as luck would have it, I found a bug in the Cocoa library when trying to play with Apple’s SourceView sample code.

The problem is that you can delete a group’s last child and not get a notification sent to your delegate’s method outlineViewSelectionDidChange:. In order to see this happen, just download the source code from Apple’s web site at http://developer.apple.com/samplecode/SourceView/ and build it or run the pre-built version of the application in the folder.

1. Select the first item under PLACES.


2. Press the “-” button to remove the selected item.


3. Keep doing this until the child nodes under PLACES is empty.


4. Notice the “-” button is still active even though there is no selection; the state of this button is updated by calls to the method outlineViewSelectionDidChange:.


5. Press the “-” button once again and notice it removes the DEVICES group.

In Step 2 and 3, the notification NSOutlineViewSelectionDidChangeNotification is sent after each removal except for when the last node is removed, thereby causing nothing to be selected; most people would define the removal of the last child a change in selection, but it appears there’s a bug in Cocoa that prevents that from happening.

I added the following code as an action method for the “-” button in order to fix this. Note that I’ve only been trying this on Mac OS X 10.5.7, so other versions of Mac OS X may work differently.

// --------------------------------------------------
// removeSelectionAction:sender:
// --------------------------------------------------
- (IBAction)removeSelectionAction:(id)sender
{
 NSArray* selectedItems;
 NSUInteger numberOfSelectedItems;
 BOOL  needToSendTheNotificationOurselves = NO;

 selectedItems = [treeController selectedNodes];
 numberOfSelectedItems = [selectedItems count];
 if (0 == numberOfSelectedItems)
 {
  // Not sure how we could have gotten here when nothing is
  // selected, so we better send out a notification to all
  // controllers that they better get on the ball.
  needToSendTheNotificationOurselves = YES;
 }
 else
 {
  NSTreeNode* firstSelectedNode;
  NSTreeNode* parentNode;

  // Let's see if the node about to be removed is the only
  // child of its parent; if so, we'll need to send out a
  // notification ourselves to the controllers to handle the
  // change.
  firstSelectedNode = [selectedItems objectAtIndex:0];
  parentNode = [firstSelectedNode parentNode];
  if (nil != parentNode)
  {
   if (1 == [[parentNode childNodes] count])
   {
    needToSendTheNotificationOurselves = YES;
   }
  }
 }

 [treeController remove:sender];

 if (needToSendTheNotificationOurselves)
 {
  NSNotification* theMissingNotificationWeNeed;

  // Looks like whatever we removed has placed us in the
  // state where we won't get the notification we would
  // normally get, so we'll have to send out a notification
  // ourselves.
  theMissingNotificationWeNeed =
   [NSNotification
    notificationWithName:
    NSOutlineViewSelectionDidChangeNotification
    object:outlineView];
  if (nil != theMissingNotificationWeNeed)
  {
   [[NSNotificationCenter defaultCenter]
    postNotification:theMissingNotificationWeNeed];
  }
 }
}