How to interrupt viewWillAppear hierarchy - ios

Question

I have a rootViewController, in it's viewDidLoad method， I initialized another two ViewController2* object and their views as subview of rootViewController.view, then I set first ViewController2* controller.view.hidden = YES.
Then, on v1 has a button handler, when touch it, it present a UINavigationController, after that touch 'dismiss' button call dismissViewControllerAnimated on v1.
The question is: when dismiss complete, the two of ViewController2* fire viewWillAppear. How to make it only fire the viewWillAppear on the visible one, but not on the hidden one?
the rootViewController's implementation:
#implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
self.v1 = [[ViewController2 alloc] init];
self.v1.title = #"v1";
[self.view addSubview:self.v1.view];
self.v1.view.hidden = YES;
self.v2 = [[ViewController2 alloc] init];
self.v2.title = #"v2";
[self.view addSubview:self.v2.view];
UIButton * btn = [UIButton buttonWithType:UIButtonTypeRoundedRect];
[btn setTitle:#"POP" forState:UIControlStateNormal];
[btn sizeToFit];
[btn addTarget:self action:#selector(touchHandler:) forControlEvents:UIControlEventTouchDown];
[self.view addSubview:btn];
}
- (void)touchHandler:(id)sender {
UINavigationController * nc= [[UINavigationController alloc] initWithRootViewController:[[UIViewController alloc] initWithNibName:nil bundle:nil]];
((UIViewController *)[nc.viewControllers objectAtIndex:0]).navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:#"dismiss" style:UIBarButtonItemStyleBordered target:self action:#selector(dismissHandler:)];
[self presentViewController:nc animated:YES completion:nil];
}
- (void) dismissHandler:(id)sender
{
[self dismissViewControllerAnimated:YES completion:nil];
}
#end
ViewController2:
#implementation ViewController2
- (void)viewWillAppear:(BOOL)animated
{
NSLog(#"%#",self.title);
}
#end

Answer 1

viewWillAppear will fire on your UIViewController's, even if the view controllers view is set hidden=YES.
You can surely test if (self.view.hidden == YES) in your viewWillAppear delegate method if you want to prevent some expensive operation from occurring, but beware that if you later make that view un-hidden, that viewWillAppear won't fire then.

Answer 2

Simple, the reason why those methods are called is because the viewController's view is part of the main window's view hierarchy. This means that it has a superview that has a superview that has a superview and so on until that superview is the main window.
Instead of hiding and unhiding the viewController views, you should instead add and remove them from their superview. Also, to make sure that viewWillAppear and viewDidAppear are called correctly at the correct times, take a look at ViewController Containment:
http://www.cocoanetics.com/2012/04/containing-viewcontrollers/