setSelectsInsertedObjects on NSArrayController not actually selecting

Question

I Have an NSArrayController bound to a NSUserDefaults controller, with setSelectsInsertedObjects set to YES in Interface Builder, but when I click Add, the previously select object gets unselected, instead of selecting the newly added object.

What am I missing?

Answer 1

That's pretty much what selectsInsertedObjects means, as I understand it. When the user adds a new item, the new item is selected, replacing the previous selection.

If you want different behavior, you could extend NSArrayController or create your own controller class that uses NSArrayController as a delegate, perhaps based on NSProxy. I believe you'd need to override add: to:

1. save the current selection
2. call the parent add:
3. merge the current selection with the saved selection
4. set the selection to the merged selection

However, I don't know enough about NSArrayController internals to say whether this would work.

Answer 2

How are you binding them? If it is through NSArrayController's 'content' binding, then I believe it tries to bind the selectionIndexes to the same object. This class (NSIndexSet) does not work with NSUserDefaults (I have no idea why, but I've had the same problem in the past - I think it has something to do with it's object lifecycle; it gets initialized as empty and then adds indexes or something). What setSelectsInsertedObjects is doing is just automatically updating the selectionIndexes when a new object is added, and basically your NSUserDefaults controller is messing that up. I'm not sure where it is, but I think if you hunt around NSArrayController's bindings you will find one for selectionIndexes (or something related) that was automatically bound to NSUserDefaults for you; if you uncheck that, things should work.