Multicast Delegate Pattern in Objective C to add multiple delegates to something

Example.m

#import "UITextViewHideKeyboardOnEnterBehaviour.h"
#import "UITextView+Multicast.h"

@implementation UITextViewHideKeyboardOnEnterBehaviour

- (id)initWithTextView:(UITextView *)textView
{
    if (self=[super init])
    {
        [textView.multicastDelegate addDelegate:self];
    }
    return self;
}

- (BOOL)textView:(UITextView *)textView shouldChangeTextInRange:(NSRange)range replacementText:(NSString *)text {
    // see: http://stackoverflow.com/questions/703754/how-to-dismiss-keyboard-for-uitextview-with-return-key
    if([text isEqualToString:@"\n"]) {
        [textView resignFirstResponder];
        return NO;
    }

    return YES;
}

-(BOOL)textViewShouldBeginEditing:(UITextView *)textView
{
    return YES;
}

@end

Mult_TextView.m

// add multicasting capabilities to a UITextView
SHCMulticastDelegate* multicast = [[SHCMulticastDelegate alloc] init];
self.textView.delegate = multicast;

// add multiple delegates
[multicast addDelegate:_someDelegateImplementation];
[multicast addDelegate:_anotherDelegateImplementation];

Multicast_Delegate.h

#import <UIKit/UIKit.h>
#import "SHCMulticastDelegate.h"

@interface UITextView (Multicast)

@property (readonly) SHCMulticastDelegate* multicastDelegate;

@end

Multicast_Delegate.m

#import "UITextView+Multicast.h"
#import <objc/runtime.h>

@implementation UITextView (Multicast)

NSString* const UITextViewMulticastDelegateKey = @"multicastDelegate";

- (SHCMulticastDelegate *)multicastDelegate
{
    // do we have a SHCMulticastDelegate associated with this class?
    id multicastDelegate = objc_getAssociatedObject(self, (__bridge const void *)(UITextViewMulticastDelegateKey));
    if (multicastDelegate == nil) {

        // if not, create one
        multicastDelegate = [[SHCMulticastDelegate alloc] init];
        objc_setAssociatedObject(self, (__bridge const void *)(UITextViewMulticastDelegateKey), multicastDelegate, OBJC_ASSOCIATION_RETAIN);

        // and set it as the delegate
        self.delegate = multicastDelegate;
    }

    return multicastDelegate;
}

@end

ScrollViewForwarding.m

#pragma mark - UIScrollViewDelegate forwarding
-(BOOL)respondsToSelector:(SEL)aSelector {
    if ([self.delegate respondsToSelector:aSelector]) {
        return YES;
    }
    return [super respondsToSelector:aSelector];
}


-(id)forwardingTargetForSelector:(SEL)aSelector {
    if ([self.delegate respondsToSelector:aSelector]) {
        return self.delegate;
    }
    return [super forwardingTargetForSelector:aSelector];
}

SHCMulticastDelegate.h

#import <Foundation/Foundation.h>

// handles messages sent to delegates, multicasting these messages to multiple observers
@interface SHCMulticastDelegate : NSObject

// Adds the given delegate implementation to the list of observers
- (void)addDelegate:(id)delegate;

@end

SHCMulticastDelegate.m

#import "SHCMulticastDelegate.h"

@implementation SHCMulticastDelegate
{
    // the array of observing delegates
    NSMutableArray* _delegates;
}

- (id)init
{
    if (self = [super init])
    {
        _delegates = [NSMutableArray array];
    }
    return self;
}

- (void)addDelegate:(id)delegate
{
    [_delegates addObject:delegate];
}

- (BOOL)respondsToSelector:(SEL)aSelector
{
    if ([super respondsToSelector:aSelector])
        return YES;

    // if any of the delegates respond to this selector, return YES
    for(id delegate in _delegates)
    {
        if ([delegate respondsToSelector:aSelector])
        {
            return YES;
        }
    }
    return NO;
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
{
    // can this class create the signature?
    NSMethodSignature* signature = [super methodSignatureForSelector:aSelector];

    // if not, try our delegates
    if (!signature)
    {
        for(id delegate in _delegates)
        {
            if ([delegate respondsToSelector:aSelector])
            {
                return [delegate methodSignatureForSelector:aSelector];
            }
        }
    }
    return signature;
}

- (void)forwardInvocation:(NSInvocation *)anInvocation
{
    // forward the invocation to every delegate
    for(id delegate in _delegates)
    {
        if ([delegate respondsToSelector:[anInvocation selector]])
        {
            [anInvocation invokeWithTarget:delegate];
        }
    }
}

@end