custom container view controller state preservation

Question

I need to create custom container viewcontroller with label and 2 states A and B(each state presented by child viewcontroller and swap each other). Both children viewcontrollers instantiates when parent container creates and currentViewController is viewControllerA by default. So i have something like this in container viewcontroller:

@property(weak, nonatomic) id currentViewController;
@property(strong, nonatomic) id viewControllerA;
@property(strong, nonatomic) id viewControllerB;
@property(strong, nonatomic) UILabel* label;

...

// Question here
- (void)viewDidLoad
{
    [super viewDidLoad];
    self.viewControllerA = [ViewControllerA new];
    self.viewControllerB = [ViewControllerB new];
    self.currentViewController = self.viewControllerA;
    [self populateCurrentViewController];
}

- (void)populateCurrentViewController
{
    [self addChildViewController:self.currentViewController];
    [self.view addSubview:self.currentViewController.view];
    [self.currentViewController didMoveToParentViewController:self];
}

- (void)goToState: (UIViewController*)stateController
{
    if(self.currentViewController != stateController)
    {
        [self.currentViewController willMoveToParentViewController:nil];
        [self addChildViewController:state];

        [self transitionFromViewController: self.currentViewController toViewController: stateController
            duration: 0.25 options:UIViewAnimationOptionTransitionFlipFromLeft
            animations:nil
            completion:^(BOOL finished) {
                [self.currentViewController removeFromParentViewController];
                [stateController didMoveToParentViewController:self];
            }];
    }
}

- (void)goToStateA
{
    [self goToState: self.viewControllerA];
    self.label.text = @"A";
}

- (void)goToStateB
{
    [self goToState: self.viewControllerB];
    self.label.text = @"B";
}

I need to preserve state of container viewcontroller. The question is where i must instantiate and add children viewcontrollers on first creating my container viewcontroller and on restoration process? Where i must restore children viewcontrollers?

I found many candidates:

-(void)initWithCoder
-(void)awakeFromNib
-(void)viewDidLoad
-(void)viewWillAppear

and

-(void)decodeRestorableStateWithCoder

for restoration process.

A couple of thoughts on this subject. If use initWithCoder and viewDidLoad for creating children viewcontrollers and adding current viewcontroller as a child to container viewcontroller, then after restoration process i need to change current viewcontroller and swap it if necessary, what is wrong i think. If use viewWillAppear for adding current viewcontroller, then it is normal for restoration process, but this method may be invoked several times.

I think there are two ways to restore restore children viewcontrollers:

1. Instantiate in viewDidLoad and restore in -(void)decodeRestorableStateWithCoder:(NSCoder *)coder like [self.viewControllerA decodeRestorableStateWithCoder:coder] (i saw it here - https://stackoverflow.com/a/16647606/2492707)

2. Full restore in -(void)decodeRestorableStateWithCoder:(NSCoder *)coder like self.viewControllerA = [coder decodeObjectForKey: @"AKey"];

Which way is better?

Understanding of the recovery process of the UINavigationController (where visibleViewController is populated) can help me too.

Thanks in advance.