I have a class capable of KVO (call it Observee ), the affectedValue property is affectedValue by the affectingValue property. The relationship between properties is determined using the +keyPathsForValuesAffectingAffectedValue method.
Setting the affectingValue value notifies that the affectedValue has changed as I expected if Ovservee not a subclass of NSObjectController . Full example:
@interface Observee : NSObject // or NSObjectController @property (readonly, strong, nonatomic) id affectedValue; @property (strong, nonatomic) id affectingValue; @property (strong, nonatomic) NSArrayController *arrayController; @end @implementation Observee @dynamic affectedValue; - (id)affectedValue { return nil; } + (NSSet *)keyPathsForValuesAffectingAffectedValue { NSLog(@"keyPathsForValuesAffectingAffectedValue called"); return [NSSet setWithObject:@"affectingValue"]; } @end @interface AppDelegate : NSObject <NSApplicationDelegate> @property (strong, nonatomic) Observee *observee; @end @implementation AppDelegate - (void)applicationDidFinishLaunching:(NSNotification *)notification { self.observee = [[Observee alloc] init]; [self.observee addObserver:self forKeyPath:@"affectedValue" options:NSKeyValueObservingOptionNew context:NULL]; NSLog(@"setting value to affectingValue"); self.observee.affectingValue = @42; } - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { NSLog(@"affected key path = %@", keyPath); } @end
The example works fine and is output like the following when Observee outputs an NSObject :
keyPathsForValuesAffectingAffectedValue called setting value to affectingValue affected key path = affectedValue
but when Observee outputs an NSObjectController :
keyPathsForValuesAffectingAffectedValue called setting value to affectingValue
(note that the "affected key path = affectedValue" is missing.)
It seems that keyPathsForValuesAffectingAffectedValue is called in both cases, but there is no-op in it.
In addition, any key paths associated with an instance (subclass) of NSObjectController will not affect other key paths, such as:
@implementation SomeObject // `someValue` won't be affected by `key.path.(snip).arrangedObjects` + (NSSet *)keyPathsForValuesAffectingSomeValue { return [NSSet setWithObject:@"key.path.involving.anNSArrayController.arrangedObjects"]; } @end
How to declare a dependency between key paths in such cases? And why is all this happening?
(Yes, I know about will/didChangeValueForKey: and friends, but wrapping each affecting key path with an (nother) installer is horrible, and I would like to avoid it.)