A basic, block-oriented pub-sub pattern in Objective-C, demonstrating typedef of blocks and use of operation queues

SimpleNotifier.h

//
//  SimpleNotifier.h
//

#import <Foundation/Foundation.h>

typedef void (^VoidBlock)();

///
/// A simple notification to-many observers
///
@interface FRSNotifier : NSObject

-(id)init;

@property (nonatomic) NSOperationQueue *operationQueue;

-(id)addObserver:(VoidBlock)block;
-(void)removeObserver:(id)token;
-(void)postNotification;

@end

SimpleNotifier.m

//
//  SimpleNotifier.m
//

#import "SimpleNotifier.h"

@implementation SimpleNotifier
{
    NSMutableDictionary *_observers;
}

///
/// Generates a new GUID
///
- (NSString *)uuidString {
    // Returns a UUID
    
    CFUUIDRef uuid = CFUUIDCreate(kCFAllocatorDefault);
    NSString *uuidString = (__bridge_transfer NSString *)CFUUIDCreateString(kCFAllocatorDefault, uuid);
    CFRelease(uuid);
    
    return uuidString;
}

///
/// Default initializer that assigned a GUID as the notification ID
/// This enables code in the app to only worry about registering with the same object, rather than with the same ID
///
-(id)init
{
    self = [super init];
    
    if(self) {
        _observers = [[NSMutableDictionary alloc] init];
    }
    
    return self;
}

///
/// Gets the operation queue used to call back observers of this object, returning the mainQueue by default
///
-(NSOperationQueue *)operationQueue
{
    if(!_operationQueue) {
        _operationQueue = [NSOperationQueue mainQueue];
    }
    
    return _operationQueue;
}

///
/// Adds an observing block of code to this notifier, which is called back when a notification is posted to this object
///
-(id)addObserver:(VoidBlock)block
{
    NSString *token = [self uuidString];
    [_observers setObject:block forKey:token];
    return token;
}

///
/// Removes an observer with the given token from this notifier
///
-(void)removeObserver:(id)token
{
    [_observers removeObjectForKey:token];
}

///
/// Posts a notification to the center for the current identifier
///
-(void)postNotification
{
    NSOperationQueue *queue = self.operationQueue;
    for (VoidBlock block in [_observers allValues]) {
        [queue addOperationWithBlock:block];
    }
}

@end