Darwin notifications listen and send for iOS

Darwin

#import <Foundation/Foundation.h>

typedef void (^DarwinNotificationBlock)(NSString *identifier);

@interface Darwin : NSObject

+ (Darwin *)sharedInstance;
- (void)startListening:(DarwinNotificationBlock)block;
- (void)test;

@end

gistfile1.m

#import "Darwin.h"

static NSString * const DarwinNotificationName = @"DarwinNotificationName";

@interface Darwin ()
@property (nonatomic, strong) DarwinNotificationBlock listenBlock;
@end

@implementation Darwin

+ (Darwin *)sharedInstance
{
    static Darwin *_sharedInstance = nil;
    static dispatch_once_t once;
    dispatch_once(&once, ^{
        _sharedInstance = [[self alloc] init];
    });

    return _sharedInstance;
}


- (instancetype)init
{
    if ((self = [super init])) {
        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didReceiveMessageNotification:) name:DarwinNotificationName object:nil];
        [self registerForNotifications];
    }
    return self;
}


- (void)startListening:(DarwinNotificationBlock)block
{
    self.listenBlock = block;
}


- (void)registerForNotifications {
    CFNotificationCenterRef const center = CFNotificationCenterGetDarwinNotifyCenter();
    CFStringRef str = (__bridge CFStringRef)@"Test_identifier";
    CFNotificationCenterAddObserver(center, (__bridge const void *)(self), notificationCallback, str, NULL, CFNotificationSuspensionBehaviorDeliverImmediately);
}


- (void)test
{
    CFNotificationCenterRef const center = CFNotificationCenterGetDarwinNotifyCenter();
    CFDictionaryRef const userInfo = NULL;
    BOOL const deliverImmediately = YES;
    CFStringRef str = (__bridge CFStringRef)@"Test_identifier";
    CFNotificationCenterPostNotification(center, str, NULL, userInfo, deliverImmediately);
}


void notificationCallback(CFNotificationCenterRef center, void * observer, CFStringRef name, void const * object, CFDictionaryRef userInfo)
{
    NSString *identifier = (__bridge NSString *)name;
    [[NSNotificationCenter defaultCenter] postNotificationName:DarwinNotificationName object:nil userInfo:@{@"identifier" : identifier}];
}


- (void)didReceiveMessageNotification:(NSNotification *)notification
{
    NSDictionary *userInfo = notification.userInfo;
    NSString *identifier = [userInfo valueForKey:@"identifier"];

    if (self.listenBlock != nil) {
        self.listenBlock(identifier);
    }
}

@end