Example program attached to Radar #

KVODependentToManyBug.m

#import <Foundation/Foundation.h>

@interface Foo : NSObject

@property (nonatomic, strong) NSArray *bars;
- (void)addBar:(NSString *)bar;
- (void)removeBar:(NSString *)bar;

@end

@interface Foo ()

@property (nonatomic, strong) NSMutableArray *internalBars;

@end

@implementation Foo

- (instancetype)init
{
	self = [super init];
	if (self) {
		_internalBars = [NSMutableArray array];
	}
	return self;
}

+ (NSSet *)keyPathsForValuesAffectingBars { return [NSSet setWithObjects:@"internalBars", nil]; }
- (NSArray *)bars { return [self.internalBars copy]; }
- (void)setBars:(NSArray *)names { self.internalBars = [names ?: @[] mutableCopy]; }

- (void)addBar:(NSString *)bar
{
	[self insertObject:bar inInternalBarsAtIndex:self.internalBars.count];
}

- (void)removeBar:(NSString *)bar
{
	NSUInteger index = [self.internalBars indexOfObject:bar];
	if (index == NSNotFound) return;
	[self removeObjectFromInternalBarsAtIndex:index];
}

- (void)insertObject:(NSString *)object inInternalBarsAtIndex:(NSUInteger)index
{
	[self.internalBars insertObject:object atIndex:index];
}

- (void)removeObjectFromInternalBarsAtIndex:(NSUInteger)index
{
	[self.internalBars removeObjectAtIndex:index];
}

@end

@interface Observer : NSObject
@end

@implementation Observer

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context
{
	NSLog(@"Change kind: %@", change[NSKeyValueChangeKindKey]);
}

@end

int main(int argc, char *argv[]) {
	@autoreleasepool {
		
		NSString *keyPathToObserve = @"bars"; // Change kind will always be NSKeyValueChangeSetting (1)
		//NSString *keyPathToObserve = @"internalBars"; // Change kind will be correct
		
		Observer *observer = [[Observer alloc] init];
		Foo *foo = [[Foo alloc] init];
		
		NSKeyValueObservingOptions options = NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld;
		[foo addObserver:observer forKeyPath:keyPathToObserve options:options context:NULL];

		[foo addBar:@"Hello"];
		[foo addBar:@"KVO"];
		[foo addBar:@"Is"];
		[foo removeBar:@"KVO"];
		[foo addBar:@"Great"];
	
		[foo removeObserver:observer forKeyPath:keyPathToObserve];
	}
}