KKWatchAppNotificationCenter.h

@import Foundation;

@interface KKWatchAppNotificationCenter : NSObject
+ (instancetype)sharedCenter;

- (void)postNotification:(NSString *)key;

- (void)addTarget:(id)target selector:(SEL)selector name:(NSString *)notification;
- (void)removeObserver:(NSObject *)observer;
@end

KKWatchAppNotificationCenter.m

#import "KKWatchAppNotificationCenter.h"

#define LFSuppressPerformSelectorLeakWarning(doPerformSelector) \
do { \
_Pragma("clang diagnostic push") \
_Pragma("clang diagnostic ignored \"-Warc-performSelector-leaks\"") \
doPerformSelector; \
_Pragma("clang diagnostic pop") \
} while (0)

@interface KKWatchAppNotificationCenter ()
{
	NSMutableDictionary *notificationKeys;
}
@end

@implementation KKWatchAppNotificationCenter

+ (instancetype)sharedCenter
{
	static KKWatchAppNotificationCenter *sharedRegister = nil;
	static dispatch_once_t onceToken;
	dispatch_once(&onceToken, ^{
		sharedRegister = [[KKWatchAppNotificationCenter alloc] init];
	});
	return sharedRegister;
}

- (instancetype)init
{
	self = [super init];
	if (self) {
		notificationKeys = [[NSMutableDictionary alloc] init];
	}
	return self;
}

- (void)postNotificationWithKey:(NSString *)key
{
	CFNotificationCenterRef const center = CFNotificationCenterGetDarwinNotifyCenter();
	CFDictionaryRef const userInfo = NULL;
	BOOL const deliverImmediately = YES;
	CFNotificationCenterPostNotification(center, (CFStringRef)key, NULL, userInfo, deliverImmediately);
}

- (void)addTarget:(id)target selector:(SEL)selector name:(NSString *)notification
{
	if (!target) {
		return;
	}

	if (!selector) {
		return;
	}

	if (!notification || ![notification length]) {
		return;
	}

	NSMutableArray *a = [notificationKeys objectForKey:notification];
	BOOL needRegisterNotification = NO;

	if (!a) {
		a = [NSMutableArray array];
		needRegisterNotification = YES;
	}

	for (NSDictionary *d in a) {
		if (d[@"target"] == target && NSSelectorFromString(d[@"selector"]) == selector) {
			return;
		}
	}

	NSDictionary *d = @{@"target": target, @"selector": NSStringFromSelector(selector)};
	[a addObject:d];

	if (needRegisterNotification) {
		[self registerNotification:notification];
		[notificationKeys setObject:a forKey:notification];
	}
}

- (void)removeObserver:(NSObject *)observer
{
	NSMutableArray *notificationsToDelete = [[NSMutableArray alloc] init];
	for (NSString *notification in notificationKeys) {
		NSMutableArray *a = notificationKeys[notification];
		NSMutableArray *objectsToDelete = [NSMutableArray array];
		for (NSDictionary *d in a) {
			id target = d[@"target"];
			if (target == observer) {
				[objectsToDelete addObject:d];
			}
		}
		[a removeObjectsInArray:objectsToDelete];
		if (![a count]) {
			[notificationsToDelete addObject:notification];
		}
	}

	for (NSString *notification in notificationsToDelete) {
		[self unregisterNotification:notification];
		[notificationKeys removeObjectForKey:notificationKeys];
	}
}

- (void)registerNotification:(NSString *)key
{
	CFNotificationCenterRef const center = CFNotificationCenterGetDarwinNotifyCenter();
	CFNotificationSuspensionBehavior const suspensionBehavior = CFNotificationSuspensionBehaviorDeliverImmediately;
	CFNotificationCenterAddObserver(center, (__bridge const void *)(self), KKWatchAppNotificationRegisterCallback, (CFStringRef)key, NULL, suspensionBehavior);
}

- (void)unregisterNotification:(NSString *)key
{
	CFNotificationCenterRef const center = CFNotificationCenterGetDarwinNotifyCenter();
	CFNotificationCenterRemoveObserver(center, (__bridge const void *)(self), (CFStringRef)key, NULL);
}

void KKWatchAppNotificationRegisterCallback(CFNotificationCenterRef center, void * observer, CFStringRef name, void const * object, CFDictionaryRef userInfo)
{
	KKWatchAppNotificationCenter *self = (__bridge KKWatchAppNotificationCenter *)observer;
	NSString *notification = (__bridge NSString *)name;

	NSArray *a = [self->notificationKeys objectForKey:notification];
	for (NSDictionary *d in a) {
		id target = d[@"target"];
		SEL action = NSSelectorFromString(d[@"selector"]);
		LFSuppressPerformSelectorLeakWarning([target performSelector:action withObject:nil]);
	}
}

@end