On May 30, 2009, at 2:18 PM, Kelvin Chung wrote:
I seem to have a very simple question, but the answer is eluding me
for some odd reason, but here goes:
Suppose I have two NSArrayControllers, ac1 and ac2. Suppose now
that I have a third controller ac3, whose content array is dependent
on both ac1.selection and ac2.selection (or some keypath therein).
Since I can't bind ac3 to both ac1 and ac2 at the same time, I have
a class which has a dependent key. In particular, suppose I have
the following:
@interface Foo {
IBOutlet NSArrayController* ac1;
IBOutlet NSArrayController* ac2;
}
/* ... */
@end
@implementation Foo
- (id) ac1Selection { return [[ac1 selection] valueForKey:@"bar"]; }
- (id) ac2Selection { return [[ac2 selection] valueForKey:@"baz"]; }
+ (NSSet*) keyPathsForValuesAffectingAc3ContentArray {
return [NSSet setWithObjects:@"ac1Selection", @"ac2Selection", nil];
}
The +keyPathsForValuesAffectingKey is, at least in theory, correct,
but it won't work. You will never receive KVO notifications when the
selection changes. Instead, why not just observe "selectedObjects" of
each array controller, and in -
observeValueForKeyPath:ofObject:change:context: send willchange/
didchange for the "ac3ContentArray" key?
- (NSArray*) ac3ContentArray {
/* Do stuff using -ac1Selection and -ac2Selection */
}
@end
Keary Suska
Esoteritech, Inc.
"Demystifying technology for your home or business"
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