Hi,
there are two possible solutions for your problem:
nr.1: observe the NSManagedObjectContext via
NSManagedObjectContextObjectsDidChangeNotification
nr.2: observe arrangedObjects of your NSArrayController (as stated
above, this is possible)
When you are recieving the notifications (either via nr1s
NSNotificationCenter or in nr2s
observeValueForKeyPath:ofObject:change:context:) in your custom control
you have the chance to update your model. For nr2s approach you have to
track the objects you are observing (via a private property of your
custom view) and update it correspondingly. Additionally you probably
want to observe keypaths of your model (to get notifications if
individual propertys of your item changed.
Pseudocode:
@interface View
{
NSArray *observedItems;
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context
{
if ( context == kMyCollectionChangedContext ) {
NSArray *changedItems = [ object valueForKey:keyPath ];
NSArray *newItems = all items from changedItems but not in
observedItems;
NSArray *removedItems = all items not in changedItems but in
observedItems;
[ self tearDownObservationOfItems:removedItems ];
[ self addObservationOfItems:newItems ];
self.observedItems = newItems;
[ self updateUI ];
}
else if ( context == kMyIndividualPropertyChangedContext ) {
track which individual property changed and update UI (in your
case modify the corresponding layer)
}
}
- (void)addObservationOfItems:(NSArray*)newItems
{
for ( id item in newItems ) {
[ item addObserver:self keyPath:theKeyPathForIndividiualProperty
options:0 context:kMyIndividualPropertyChangedContext ];
}
}
- (void)tearDownObservationOfItems:(NSArray*)oldItems
{
for ( id item in oldItems ) {
[ item removeObserver:self
forKeyPath:theKeyPathForIndividiualProperty ];
}
}
You can easily add additional individual properties in
addObservationOfItems:, just add your view as an observer for the
corresponding keypath.
Regards, Markus
Am 23.08.10 09:32, schrieb Ajay Sabhaney:
I'm guessing, but you seem to have a managed object with a to-many
relationship, and you want to be notified whenever anything is added to or
removed from that relationship property. So, observe that property of the
managed object, and you're done.
If there's something more complicated going on in the data model, your solution
may be more complex, but throwing NSArrayController at the problem is highly
unlikely to help with the solution.
Quincey, thank you for the follow up. I do not think I explained my situation
clearly so I will try and explain this more clearly.
I have a very simple data model. There is only one entity: Item. Each time I
add or remove an Item to the array controller source, I would like my UI view
to take action based on the newly added/removed Item. More specifically: I
have a very custom view, and each Item entity in the data model corresponds to
a Core Animation layer in the view. So if a particular Item entity is removed
from the array controller, I'd like to remove a corresponding CALayer from the
layer-hosting view. And if a particular Item entity is added to the array
controller, I'd like to add a corresponding CALayer to the layer-hosting view.
Currently, my view is observing the arrangedObjects property of
NSArrayController. However, all KVO notifications that the view receives are
NSKeyValueChangeSetting type changes (as opposed to NSKeyValueChangeInsertion
type changes). I would like them to be NSKeyValueChangeInsertion changes so
that I may easily add a CALayer corresponding to the newly added Item model.
So to overcome this, I binded the contentArray property of the
NSArrayController to a mutable array of mine. So each time I add an Item to
the mutable array, the NSArrayController notifies my view, which takes the
appropriate action.
[ I am doing something somewhat similar to what you see on the LAST post in
this thread to ensure I receive NSKeyValueChangeInsertion type changes:
http://stackoverflow.com/questions/1313709 ]
In case you're wondering why I'm using an NSArrayController and not just an
array, it is because NSArrayController currently ties in nicely with file
loading and saving, as well as undo and redo. I'm also using some of the
selection functionality that NSArrayController provides.
Thinking about this a little more carefully, I'm not sure that using an
NSArrayController actually is the best solution in this situation, especially
as the data model and the view become more complex....
Comments and suggestions in relation to this as well as my original post are
appreciated_______________________________________________
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