Switching ViewControllers with UISegmentedControl

- (void)viewDidLoad {
    [super viewDidLoad];
    // add viewController so you can switch them later. 
    UIViewController *vc = [self viewControllerForSegmentIndex:self.typeSegmentedControl.selectedSegmentIndex];
    [self addChildViewController:vc];
    vc.view.frame = self.contentView.bounds;
    [self.contentView addSubview:vc.view];
    self.currentViewController = vc;
}
- (IBAction)segmentChanged:(UISegmentedControl *)sender {
    UIViewController *vc = [self viewControllerForSegmentIndex:sender.selectedSegmentIndex];
    [self addChildViewController:vc];
    [self transitionFromViewController:self.currentViewController toViewController:vc duration:0.5 options:UIViewAnimationOptionTransitionFlipFromBottom animations:^{
        [self.currentViewController.view removeFromSuperview];
        vc.view.frame = self.contentView.bounds;
        [self.contentView addSubview:vc.view];
    } completion:^(BOOL finished) {
        [vc didMoveToParentViewController:self];
        [self.currentViewController removeFromParentViewController];
        self.currentViewController = vc;
    }];
    self.navigationItem.title = vc.title;
}

- (UIViewController *)viewControllerForSegmentIndex:(NSInteger)index {
    UIViewController *vc;
    switch (index) {
        case 0:
            vc = [self.storyboard instantiateViewControllerWithIdentifier:@"FooViewController"];
            break;
        case 1:
            vc = [self.storyboard instantiateViewControllerWithIdentifier:@"BarViewController"];
            break;
    }
    return vc;
}