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Question about KVO - jotapeh - Jul 16, 2011 09:09 AM

Hey guys, first time poster

Just wondering - I'm trying to write a pixeling program and learning quite a lot from the Apple Sketch demo code as I go. It has a comment in SKTWindowController.h that says this:

This class is KVC and KVO compliant for this key:

"graphicsController" (an NSArrayController; read-only) - The controller that manages the selection for the graphic view in the controlled window.

But I can't find a pair of graphicsController/setGraphicsController functions, or a synthesize declaration, or even an @property or an override of willChangeValueForKey.. nothing.

How is this possible? I don't get how you can be KVC and KVO compliant without any of this. Huh


RE: Question about KVO - SethWillits - Jul 16, 2011 11:19 AM

"If no accessor is found, and the receiver’s class method accessInstanceVariablesDirectly returns YES, the receiver is searched for an instance variable whose name matches the pattern _<key>, _is<Key>, <key>, or is<Key>, in that order."

"+ (BOOL)accessInstanceVariablesDirectly
Return Value
YES if the key-value coding methods should access the corresponding instance variable directly on finding no accessor method for a property, otherwise NO.

The default returns YES."

So there you go. But that's a bad practice IMO. If you're publicly exposing it you should be using public setter/getters so that it's obviously bindable.

RE: Question about KVO - jotapeh - Jul 16, 2011 02:24 PM

Ahh thank you. Man that's sneaky!