NSArrayController binding question

FROM : Arved von Brasch
DATE : Sun Jun 04 04:25:26 2006

Hello Cocoa Mailing List,

I have a NSManagedObject subclass (A) which has a to-many 
relationship with another NSManagedObject subclass (B).  Both are 
controlled by NSArrayControllers.

It used to be the case that I could bind the contentSet of the second 
NSArrayController (B) to the selection proxy object of the first (A) 
with the correct keypath for the relationship and everything worked 
fine.  However, the model changed slightly meaning that that the 
object selected in the first TableView was not necessarily in the 
NSArrayController (A) that controls the dynamic list.  Some of A's 
objects became permanent and thus I had to remove them from the 
content of the NSArrayController and then put them back manually 
using the TableView's DataSource methods.  This basically means that 
the selection proxy object is no longer viable to bind the second 
NSArrayController's (B) contentSet to, because the selection may be 
outside of the content of the first NSArrayController.

No problem, I thought.  As the first (A) NSArrayController has access 
to the permanent objects, even if they don't appear in its list, I 
created a new public key-value compliant method for the real selected 
object.  That is when the selection is changed in the table, the 
NSArrayController is notified and checks to see what the selection 
is, setting the real selected object using these methods.  This part 
I am sure works fine.  I have tested it extensively in other aspects 
of the program, and I can guarantee that it correctly points to the 
real selected object.  This, however, does not seem to work as a 
binding value for the second NSArrayController (B).  The second 
NSArrayController appears to work correctly, in that you can add 
objects to it, but then they seem to disappear into a void, as run-
time errors about the index being out of bounds occur if you try to 
do anything with these new objects.  The new objects will also 
disappear if the selection in the first tableView (A) is changed and 
then changed back again.

This is the code from the first NSArrayController subclass (A):

- (void)selectionChanged: (NSNotification *)notification {
   // Permanent object is always at top  -  Additional permeant objects 
will be added when I get this working.
   if ([theTable selectedRow] == 0)
       [self setRealSelection: theObject];
   else
       [self setRealSelection: [[self arrangedObjects] objectAtIndex: 
[theTable selectedRow] -1]];
}

NSManagedObject *_realSelection = nil;

- (void)setRealSelection: (NSManagedObject *)value {
   _realSelection = value;
}

- (NSManagedObject *)realSelection {
   return _realSelection;
}

The binding for the second NSArrayController (B) is using Controller 
Key 'realSelection' with the model key path being the same as when 
selection was the controller key.

I'm clearly doing something wrong, but I can't work out what it is. 
Can anyone help?

Cheers,

Arved von Brasch