   UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];  UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];   UIViewController *sidebarViewController = nil;  UIView *sidebarView = nil;   if (self.presenting) {    sidebarViewController = toVC;   sidebarView = sidebarViewController.view;   [transitionContext.containerView addSubview:sidebarView];  }  else {    sidebarViewController = fromVC;   sidebarView = sidebarViewController.view;  }   sidebarView.frame = [transitionContext finalFrameForViewController:sidebarViewController];   