ViewControllerTransitionsPart3-2

TTNavigationController.m

@interface TTNavigationController ()

@property (nonatomic, weak) UIViewController* mostRecentController;

@end

// ...

- (id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC
{
	SEL selector = @selector(navigationController:animationControllerForOperation:fromViewController:toViewController:);
	id<UIViewControllerAnimatedTransitioning> result = nil;
	if([fromVC respondsToSelector:selector])
	{
	        result = [(id<UINavigationControllerDelegate>)fromVC navigationController:navigationController
	                                                  animationControllerForOperation:operation
	                                                               fromViewController:fromVC
	                                                                 toViewController:toVC];
		if(result)
			self.mostRecentController = fromVC;
	}
	else if([toVC respondsToSelector:selector])
	{
	        result = [(id<UINavigationControllerDelegate>)toVC navigationController:navigationController
	                                                animationControllerForOperation:operation
	                                                             fromViewController:fromVC
	                                                               toViewController:toVC];
		if(result)
			self.mostRecentController = toVC;
	}
	
	return result;
}