Adding block callback functionality to UIButton.

UIButton+MOBlockCallbacks.h

#import <UIKit/UIKit.h>

typedef void (^MOButtonCallback)(id sender);

@interface UIButton (MOBlockCallbacks)

// Adds a block callback for a set of UIControlEvents. This method returns an opaque token which
// can be used to remove the callback.
- (id)mo_addCallback:(MOButtonCallback)callback forControlEvents:(UIControlEvents)events;

// Removes a callback registered in addCallback:forControlEvents:.
- (void)mo_removeCallback:(id)callbackToken;

@end

UIButton+MOBlockCallbacks.m

#import <objc/runtime.h>
#import "UIButton+MOBlockCallbacks.h"

static NSString *MOBlockCallbacksKey = @"com.mobiata.ButtonBlockCallbacks";

@interface MOButtonCallbackTrampoline : NSObject
@property (nonatomic, assign) UIControlEvents controlEvents;
@property (nonatomic, copy) MOButtonCallback callback;
@property (nonatomic, strong) id token;
@end

@implementation MOButtonCallbackTrampoline
- (void)performCallback:(id)sender
{
    [self callback](sender);
}
@end


@implementation UIButton (MOBlockCallbacks)

- (id)mo_addCallback:(MOButtonCallback)callback forControlEvents:(UIControlEvents)events
{
    if (callback == nil)
    {
        return nil;
    }

    NSMutableArray *callbacks = objc_getAssociatedObject(self, (__bridge const void *)(MOBlockCallbacksKey));
    if (callbacks == nil)
    {
        callbacks = [[NSMutableArray alloc] init];
        objc_setAssociatedObject(self, (__bridge const void *)(MOBlockCallbacksKey), callbacks, OBJC_ASSOCIATION_RETAIN);
    }

    MOButtonCallbackTrampoline *trampoline = [[MOButtonCallbackTrampoline alloc] init];
    [trampoline setControlEvents:events];
    [trampoline setCallback:callback];
    [trampoline setToken:[[NSProcessInfo processInfo] globallyUniqueString]];
    [callbacks addObject:trampoline];
    
    [self addTarget:trampoline action:@selector(performCallback:) forControlEvents:events];
    
    return [trampoline token];
}

- (void)mo_removeCallback:(id)callbackToken
{
    NSMutableArray *callbacks = objc_getAssociatedObject(self, (__bridge const void *)(MOBlockCallbacksKey));
    for (NSUInteger i = 0; i < [callbacks count]; i++)
    {
        MOButtonCallbackTrampoline *trampoline = [callbacks objectAtIndex:i];
        if ([[trampoline token] isEqual:callbackToken])
        {
            [self removeTarget:trampoline action:@selector(performCallback:) forControlEvents:[trampoline controlEvents]];
            [callbacks removeObjectAtIndex:i];
            break;
        }
    }
}

@end