Dynamic KVO Handler method

gistfile1.txt

- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context;
{
    if (context == kTBBookStoreCollectionViewCellObservingContext)
    {
        if (object == self.bookStoreItem)
        {
            NSString *observationSelectorName = [NSString stringWithFormat:@"%@DidChangeFromValue:toValue:", keyPath];
            SEL observationSelector = NSSelectorFromString(observationSelectorName);
            if ([self respondsToSelector:observationSelector])
            {
                NSMethodSignature *methodSignature = [self methodSignatureForSelector:observationSelector];
                NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:methodSignature];
                invocation.selector = observationSelector;
                
                id oldValue = [change valueForKey:NSKeyValueChangeOldKey];
                id newValue = [change valueForKey:NSKeyValueChangeNewKey];
                
                oldValue = [oldValue isEqual:[NSNull null]] ? nil : oldValue;
                newValue = [newValue isEqual:[NSNull null]] ? nil : newValue;
                
                [invocation setArgument:&oldValue atIndex:2];
                [invocation setArgument:&newValue atIndex:3];
                
                [invocation invokeWithTarget:self];
            }
        }
    }
    else
    {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}