Event queue I wrote to make a block run after all conditions have been met. For example, removing a complex loading animation after the animation has finished and the data has loaded.

KHEventQueue.h

//
//  KHEventQueue.h
//
//  Created by Kyle Howells on 04/08/2014.
//  Copyright (c) 2014 Kyle Howells. All rights reserved.
//

#import <Foundation/Foundation.h>

typedef void (^KHEventBlock)(void);

@interface KHEventQueue : NSObject
+(instancetype)sharedInstance;


-(void)eventHappened:(NSString*)event;

// Block = code to run after all events have fired.
// requirements = array of NSString's.
-(void)addBlock:(KHEventBlock)block withRequirements:(NSArray*)requirements;
@end

KHEventQueue.m

//
//  KHEventQueue.m
//
//  Created by Kyle Howells on 04/08/2014.
//  Copyright (c) 2014 Kyle Howells. All rights reserved.
//

#import "KHEventQueue.h"



NSString * const KH_EVENT_BLOCK_KEY = @"BLOCK_KEY";
NSString * const KH_EVENT_REQUIREMENTS_KEY = @"REQUIREMENTS_KEY";
#define BLOCK_KEY			KH_EVENT_BLOCK_KEY
#define REQUIREMENTS_KEY	KH_EVENT_REQUIREMENTS_KEY



@implementation KHEventQueue{
	NSOperationQueue *accessQueue;
	NSMutableArray *dictionarysWaiting;
}

+(instancetype)sharedInstance {
	static dispatch_once_t pred;
	static id shared = nil;
	
	dispatch_once(&pred, ^{
		shared = [[self alloc] init];
	});
	
	return shared;
}

-(instancetype)init{
	if (self = [super init]) {
		accessQueue = [[NSOperationQueue alloc] init];
		accessQueue.maxConcurrentOperationCount = 1;
		accessQueue.name = @"Custom Event Queue";
		[accessQueue setSuspended:NO];
		
		dictionarysWaiting = [[NSMutableArray alloc] init];
	}
	
	return self;
}






-(void)addBlock:(KHEventBlock)block withRequirements:(NSArray*)requirements{
	NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];
	
	NSMutableArray *mutableCopy = [requirements mutableCopy];
	[dictionary setObject:mutableCopy forKey:REQUIREMENTS_KEY];
	[mutableCopy release];
	
	KHEventBlock blockCopy = [block copy];
	[dictionary setObject:blockCopy forKey:BLOCK_KEY];
	[blockCopy release];
	
	[accessQueue addOperationWithBlock:^{
		[dictionarysWaiting addObject:dictionary];
	}];
}



-(void)eventHappened:(NSString*)event{
	[accessQueue addOperationWithBlock:^{
		for (NSInteger index = dictionarysWaiting.count - 1; index >= 0 ; index--)
		{
			NSDictionary *dicationary = dictionarysWaiting[index];
			
			NSMutableArray *array = dicationary[REQUIREMENTS_KEY];
			for (NSInteger i = array.count - 1; i >= 0 ; i--) {
				NSString *string = array[i];
				if ([string isEqualToString:event]) {
					[array removeObjectAtIndex:i];
				}
			}
			
			
			if (array.count == 0) {
				KHEventBlock block = dicationary[BLOCK_KEY];
				if (block != nil) {
					block();
				}
				[dictionarysWaiting removeObjectAtIndex:index];
			}
		}
	}];
}

@end