Flipping UIButton

gistfile1.m

/* Here is that block definition from above */

    UIButtonFlipActionBlock flipButtonAction = ^(id sender) {

        //get the alternate button & container
        UIButton *otherButton = (UIButton *)objc_getAssociatedObject(sender, &UIButtonFlipAltButtonKey);
        UIView *container = (UIView *)objc_getAssociatedObject(sender, &UIButtonFlipContainerViewKey);
        
        //figure out our transition
        NSNumber *transitionNumber = (NSNumber *)objc_getAssociatedObject(sender, &UIButtonFlipTransitionKey);
        UIViewAnimationTransition transition = (UIViewAnimationTransition)[transitionNumber intValue];
                
        [UIView animateWithDuration:duration animations:^ {
            
            [UIView setAnimationTransition:transition forView:container cache:YES];
            [UIView setAnimationCurve:curve];
            
            //the view has the last retain count on the sender button, so we need to retain it first
            objc_setAssociatedObject(otherButton, &UIButtonFlipAltButtonKey, sender, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            
            [sender removeFromSuperview];
            [container addSubview:otherButton];
            
            //sender no longer needs to retain the other button, because the view now is...
            objc_setAssociatedObject(sender, &UIButtonFlipAltButtonKey, otherButton, OBJC_ASSOCIATION_ASSIGN);
            
        }];
        
        //call the original button handler
        [target performSelector:selector withObject:self];
    };

UIButtonCHButtonFlip.h

@interface UIButton (CHFlipButton)

+ (UIView *)flipButtonWithFirstImage:(UIImage *)firstImage 
                         secondImage:(UIImage *)secondImage
                     firstTransition:(UIViewAnimationTransition)firstTransition
                    secondTransition:(UIViewAnimationTransition)secondTransition
                      animationCurve:(UIViewAnimationCurve)curve
                            duration:(NSTimeInterval)duration
                              target:(id)target
                            selector:(SEL)selector;


@end