Re: NSArrayController, managedObjects and KVO

FROM : Quincey Morris
DATE : Tue Mar 25 21:29:54 2008

On Mar 25, 2008, at 12:04, Brian Krisler wrote:

> I have an NSArrayController in a NIB that contains Core Data Entities.
> The represented entity has a two values, a boolean and a name, and
> these are displayed in a table as a checkbox and text. (two columns).
>
> All I would like to do is get notified with the check box is 
> selected and
> have a way of determining with item was selected.
>
> In my UI controller, I created an IBOutlet for my NSArrayController,
> then in IB, I created the binding.  Then in my UI controller's
> awakeFromNib, I add and observer to my array controller.
>
> While this appears to somewhat work, my observer gets notified 
> whenever a
> row in my table is selected, I can not figure out how to determine if
> the checkbox value changed.  Since selected the text in the table also
> fires a selection observable.
>
> I have tried different values for my keyPath: arrangedObjects, 
> selectedObjects, selection
> and in every instance, I get the same results.  If I expand the 
> keyPath
> (i.e. selection.isSelected), I expected that to notify on the 
> selection of the isSelected boolean
> field, however this is also not the case.  I found I could put 
> anything in the keyPath
> and get the same results. (selection.blah)
>
> I found in the archive a thread  indicating that for 
> NSArrayControllers, the source array,
> not the managed object array should be watched.  I have to admit, I 
> have been unsuccessful
> in learning which binding is the source array, so I appear to be 
> missing something there.
> At this point, I feel like I am just chasing my tail.


You're not entirely clear whether your ultimate goal is to find out 
when the value of the boolean changes, or to find out which rows of 
the table view are selected.

If you just want to know if the boolean changes, then the selection 
doesn't matter and the array controller doesn't enter the picture -- 
you simply arrange to observe suitable objects in your core data 
model. How you do this depends on the model. You might explicitly 
observe that boolean property of every object that has it, or you 
might observe a parent object's to-many relationship that represents 
the collection of objects having the boolean property (and is also 
what you're binding the array controller to, I assume).

Finding out which objects are selected is a bit different, because 
this information is in the user interface (the table view), not in the 
core data model. In that case, you can observe the array controller's 
selection or selectedObjects as a way of finding out *when* the 
selection changes. When that happens, if you need to know what core 
data model objects are actually selected, selectedObjects is the 
answer. Or if you need to know which table rows are selected, you can 
use table view methods like selectedRow to query the information. 
(I've always just assumed that table view properties are not 
themselves KVC-compliant, and therefore not directly observable, but I 
could easily be wrong about that. In that case, you could observe the 
table view instead of the array controller. But I suspect you don't 
really care about the selection anyway.)