Question

I am using the containment API to create a custom container view controller

Creation of Parent View Controller in ViewDidLoad of Parent, and Setting of Child View Controllers:

[self addChildViewController:newA];
[self addChildViewController:newB];
[self addChildViewController:newC];

Now once these childVC have been added I can transition using:

[self transitionFromViewController:from
                  toViewController:to
                          duration:1.0
                           options:UIViewAnimationOptionTransitionFlipFromLeft
                        animations:nil
                        completion:^(BOOL b){
                            [to didMoveToParentViewController:self];
                            [from.view removeFromSuperview];
                            [from removeFromParentViewController];
                        }];

My question now is must I remove the current childVC from the parentVC to show the new VC?

                        completion:^(BOOL b){
                            [to didMoveToParentViewController:self];
                            [from.view removeFromSuperview];
                            [from removeFromParentViewController];
                        }

Is there a way that I can preserve those childVCs’ and simply do swipe/button-action to then navigate between these childVCs’?

Answer 1

So you don’t need to remove the from view controller’s view from the view hierarchy manually. This method handles that for you upon completion of your animation block. From the docs on this method:

This method adds the second view controller’s view to the view
hierarchy and then performs the animations defined in your animations
block. After the animation completes, it removes the first view
controller’s view from the view hierarchy.

As a caveat to this, though, the animation block cannot be NULL as it is in your code example (that being said, you have nil, not NULL, which doesn’t make sense since the animations parameter is a block, not an Objective-C object).

UPDATE: Depending on your implementation, viewDidLoad may get called repeatedly if the memory for that view is cleaned up. A UITabBarController, for instance, generally only calls viewDidLoad upon adding your VC’s to the tab bar, and just calls viewWill/DidAppear after that. Similarly, a UINavigationController won’t call viewDidLoad when you pop to a view controller because it’s been maintaining it in its navigation stack, but will call viewDidLoad if you pop off of a VC and then push it back on (usually). If you’re not getting the behavior you want, you can subclass this method in your container implementation.

** NOTE I am removing the iphone-sdk-4.0 tag from your question, as the containment API did not become available until 5.0