Obj-C Preferences Observation

AGKVOReceptionist.h

typedef void (^KVOReceptionistBlock)(NSString *keyPath, id object, NSDictionary *change);

@interface AGKVOReceptionist : NSObject
{
	id _observedObject;
	NSString * _observedKeyPath;
	KVOReceptionistBlock _handler;
	BOOL _cancelled;
}


+ (instancetype)receptionistForKeyPath:(NSString *)keyPath object:(id)obj handler:(KVOReceptionistBlock)block;
- (void)cancel;

@property (nonatomic, readonly, getter=isCancelled) BOOL cancelled;

@end

AGKVOReceptionist.m

#import "AGKVOReceptionist.h"

@implementation AGKVOReceptionist

+ (instancetype)receptionistForKeyPath:(NSString *)keyPath object:(id)obj handler:(KVOReceptionistBlock)handler;
{
	AGKVOReceptionist * rc = [[[AGKVOReceptionist alloc] init] autorelease];
	rc->_handler = [handler copy];
	rc->_observedKeyPath = [keyPath copy];
	rc->_observedObject = [obj retain];
	[obj addObserver:rc forKeyPath:keyPath options:0 context:[AGKVOReceptionist class]];
	return rc;
}


- (void)dealloc;
{
	[self cancel];
	[super dealloc];
}


- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
	if (context == [AGKVOReceptionist class]) {
		if (object == _observedObject && [keyPath isEqual:_observedKeyPath]) {
			_handler(keyPath, object, change);
		}
	} else {
		[super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
	}
}


- (void)cancel;
{
	if (_observedObject) {
		[_observedObject removeObserver:self forKeyPath:_observedKeyPath context:[AGKVOReceptionist class]];
		[_observedObject release];
		[_observedKeyPath release];
		[_handler release];
		
		_observedObject = nil;
		_observedKeyPath = nil;
		_handler = nil;
		
		_cancelled = YES;
	}
}


- (BOOL)isCancelled;
{
	return _cancelled;
}


@end

Preferences Observation.m

@interface AQPreferencesObservationInfo : NSObject <NSCopying>
@property (nonatomic, readwrite, assign) void * observer;
@property (nonatomic, readwrite, copy) NSString * prefKey;
@end


@implementation AQPreferences
{
	NSMutableDictionary * observations;
}


+ (instancetype)sharedInstance
{
	static AQPreferences * shared = nil;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
		shared = [[AQPreferences alloc] init];
		shared->observations = [[NSMutableDictionary alloc] init];
	});
	return shared;
}


+ (void)addObserver:(id)observer forKey:(NSString *)prefKey handler:(void (^)(void))handler
{
	[AQPreferences.sharedInstance addObserver:observer forPreferenceKey:prefKey handler:handler];
}


+ (void)removeObserver:(id)observer forKey:(NSString *)prefKey
{
	[AQPreferences.sharedInstance removeObserver:observer forPreferenceKey:prefKey];
}



- (void)addObserver:(id)observer forPreferenceKey:(NSString *)prefKey handler:(void (^)(void))handler
{
	AQPreferencesObservationInfo * info = [[[AQPreferencesObservationInfo alloc] init] autorelease];
	info.observer = observer;
	info.prefKey = prefKey;
	
	@synchronized (self) {
		AGWeak * weakObserver = [AGWeak ref:observer];
		AGKVOReceptionist * receptionist = [AGKVOReceptionist receptionistForKeyPath:NSSTRF(@"values.%@", prefKey) object:NSUserDefaultsController.sharedUserDefaultsController handler:^(NSString *keyPath, id object, NSDictionary *change) {
			
			id strongObserver = [weakObserver.ref retain];
			if (strongObserver) {
				handler();
				[strongObserver release];
				
			} else {
				@synchronized (self) {
					AGKVOReceptionist * r = [observations objectForKey:info];
					[r cancel];
					[observations removeObjectForKey:info];
				}
			}
		}];
		
		[observations setObject:receptionist forKey:info];
	}
}


- (void)removeObserver:(id)observer forPreferenceKey:(NSString *)prefKey
{
	AQPreferencesObservationInfo * info = [[[AQPreferencesObservationInfo alloc] init] autorelease];
	info.observer = observer;
	info.prefKey = prefKey;
	
	@synchronized (self) {
		AGKVOReceptionist * r = [observations objectForKey:info];
		[r cancel];
		[observations removeObjectForKey:info];
	}
}


@end





@implementation AQPreferencesObservationInfo

- (void)dealloc
{
	[_prefKey release];
	[super dealloc];
}


- (id)copyWithZone:(NSZone *)zone
{
	return [self retain];
}


- (BOOL)isEqual:(id)object
{
	if ([object isKindOfClass:[AQPreferencesObservationInfo class]]) return NO;
	AQPreferencesObservationInfo * other = object;
	return _observer == other->_observer && [_prefKey isEqual:other.prefKey];
}


- (NSUInteger)hash
{
	return (NSUInteger)_observer ^ _prefKey.hash;
}

@end