Why is the view of viewController B added to the view of viewController A? If you are meaning to add a view to viewController A, you can do that by allocating a new UIView and displaying that on top of the current view.
On the other hand if you are trying to transition from one view controller to another, i.e going from A to B and then back to A, you should use a UINavigationController as specified in the View Controller Programming Guide in the Apple Documentation.
Source: View Controller Programming Guide
EDIT: If you want to use [[self parentViewController] yourMethodHere];
you will need a view hierarchy, for which you can use the UINavigationController. In your current scheme there is no hierarchy built so there is no parent view controller.