On May 19, 2010, at 2:05 AM, Mazen M. Abdel-Rahman wrote: > I have a custom view class with an array property. I want to bind that array > property to a model - which in my case is an array that is in a > container/manager object. The binding is done via a custom view controller > (in it's awakeFromNib). (calendar is the model object) > > [calendarView bind:@"events" > toObject:calendar > withKeyPath:@"events" > options:options]; > > Now whenever "events" in the object calendar is modified "events" in > calendarView is modified as well. > > In addition - observeValueForKeyPath... is getting called as well in the > calendarView. > > The problem is that if some items are removed from calendar's (the model) > "events array" by the time observeValueForKeyPath in calendarView gets > called its "events" array has already been updated to reflect the model > change.
I think you have two options: * Override -bind:toObject:withKeyPath:options: and don't rely on the default implementation, at all. * Use the default implementation but don't use -observeValueForKeyPath:ofObject:change:context: to be informed about the change of the view's property. Use the property's setter method, instead. I would not expect that the view's property would already be updated at the time that -observeValueForKeyPath:... is called, because by what mechanism other than that method would the binding update that property? The answer, I guess, is that the default implementation of -bind:... is actually setting some other object (not the receiver) as the key-value observer of the key path of the observableController, and that object is getting the -observeValueForKeyPath:... message and then setting the property on your view. However, if that's the case, I don't know why your view would have -observeValueForKeyPath:... invoked on it, too. So, there's a bit of a mystery there. And that's reason enough not to rely on the default implementation -- it's a black box with ill-defined behavior. Overriding -bind:... is actually the method illustrated in Apple's documentation about implementing a custom binding on a custom view. See the "How Do Bindings Work?" section of the Cocoa Bindings Programming Topics. Also, have a look at the Sketch+Accessibility sample code, where it implements custom binding (e.g. SKTGraphicView). It actually illustrates both approaches. Regards, Ken _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
