Need assistance regarding transitionFromView:toView:duration:options:completion: - ios

Question

Regarding transitionFromView:toView:duration:options:completion: Apple doc says this in last few lines:
This method modifies the views in their view hierarchy only. It does
not modify your application’s view controllers in any way. For
example, if you use this method to change the root view displayed by a
view controller, it is your responsibility to update the view
controller appropriately to handle the change.
If a ViewController has 2 full screen size views display one at a time then no issues:
[transitionFromView:self.view toView:self.view2...
but what this means it is your responsibility to update the view controller appropriately to handle the change?
if I do this:
secondViewController *sVc = [[secondViewController alloc]init];
[transitionFromView:self.view toView:sVc.view...
how its my responsibility to update the view controller appropriately to handle the change? or how to update ViewController?
UPDATE
I created a single view projec, add secondVC then in firstVC on button tap i did this:
self.svc = [[secondVC alloc]init];
[UIView transitionFromView:self.view toView:self.svc.view duration:1.0 options:UIViewAnimationOptionTransitionFlipFromLeft completion:^(BOOL finished) {}];
... secondVC viewDidLoad is working its nslog is working.
Then how to handle updating of viewcontroller?

Answer 1

The statement "it is your responsibility to update the view controller appropriately to handle the change." it meant that you have to appropriately call view hierarchy delegate methods such as:
- (void)viewDidLoad;
- (void)viewDidUnload;
- (void)viewWillAppear;
- (void)viewDidDisappear;
And other methods that are responsible for proper view management.
Here are some examples.

Answer 2

When we use transitionFromView:toView:duration:options:completion: we are only
bringing toView up in view hierarchy. but Apple says we should handle updating
of ViewControllers which are parent of these views.
Maintaining viewcontroller in navigationcontroller stack...
For .ex: if You have TabController in your application,
somewhere at tabIndex two you required to show view of viewcontroller at tabindex 1,
then you should update your tabIndex when you will use transitionfromview method
[UIView transitionFromView:fromView
toView:toView
duration:0.5
options:(controllerIndex > tabBarController.selectedIndex ? UIViewAnimationOptionTransitionCurlUp : UIViewAnimationOptionTransitionCurlDown)
completion:^(BOOL finished) {
if (finished) {
tabBarController.selectedIndex = controllerIndex;
}
}];