When you add view of viewController as subview you need also register your viewController as child view controller for parentViewController.
Example:
UIViewController *mainVC = [UIViewController new];
UIViewController *childVC = [UIViewController new];
[mainVC addChildViewController:childVC];
[mainVC.view addSubview:childVC.view];
UIViewController *parentVC = childVC.parentViewController;
Here parentVC is mainVC.