Adding and removing child view controllers

childviewcontrollers.m

// These methods assume that `self` references a UIViewController instance.

- (void)loadChildViewController:(UIViewController *)viewController
{
    [self addChildViewController:viewController];
    [self.view addSubview:viewController.view];
    [viewController didMoveToParentViewController:self];
}

- (void)unloadChildViewController:(UIViewController *)viewController
{
    [viewController willMoveToParentViewController:nil];
    [viewController.view removeFromSuperview];
    [viewController removeFromParentViewController];
}