Key-Observing, change, and NSNull
Key-Observing, change, and NSNull
- Subject: Key-Observing, change, and NSNull
- From: Edwin Vane <email@hidden>
- Date: Thu, 11 Aug 2005 09:31:55 -0400
- Mail-followup-to: Cocoa-Dev <email@hidden>
Hi,
Doing some google and apple lists searching I've found a few people with
this problem but no real resolution. Perhaps somebody will know the
answer now.
I have a custom view in which I've overridden the bind method to set up
observers for things in an NSObjectController instance. After the nib
containing my views and the NSObjectController is loaded, I call bind
the following way:
[tempoView bind: @"viewLoc" toObject: tempoTimeController
withKeyPath:@"selection.viewLoc" options:nil];
[tempoView bind: @"unitsPerPixel" toObject: tempoTimeController
withKeyPath: @"selection.unitsPerPixel" options:nil];
The content outlet of the object controller has been set properly in IB.
I add observers in the overridden bind method as follows:
[_observedObjectForViewLoc addObserver:self
forKeyPath:_observedKeyPathForViewLoc
options:NSKeyValueObservingOptionNew
context:ViewLocContext];
Please note that viewLoc is an NSPoint and the unitsPerPixel is a simple
float.
Now, observeValueForKeyPath is being triggered when a change happens
except the value of the NSKeyValueChangeNewKey key in the change
dictionary is always NSNull. I access the dictionary this way:
[change objectForKey:NSKeyValueChangeNewKey]
What I don't understand is this whole process is very similar to the
GraphicsBinding example at:
http://homepage.mac.com/mmalc/CocoaExamples/controllers.html
and yet they are able to get correct NSRect change values. Any ideas why
my change values aren't appearing correctly?
--
Edwin Vane
MMath Candidate
Computer Graphics Lab
School of Computer Science
University of Waterloo
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