#view controllers

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The ability have container views in iOS 6 storyboards is pretty cool. However, by default a container view can only have one child view controller. If you want the container view to manage multiple child view controllers you need to do a little more work. But it can still be done without leaving the world of storyboards. The main problem is that you can only have one **embed** segue from a container view. You can, however, create multiple **custom** segues from the single container view. Much of this solution is adapted from [Peregrin Planet's Container View Controllers in the Storyboard](http://orderoo.wordpress.com/2012/02/23/container-view-controllers-in-the-storyboard/). My solution is slightly different in that the container view doesn't use the full screen and is controlled externally. But the core concepts of the solution are the same. Here are screenshots of the finished application.   The container view at the bottom of the screen switches between one of two child view controllers. The storyboard looks like this.  Notice we have a regular container view with a regular embedded container view controller. The `ContainerViewController` is in turn connected to two child view controllers. The segue between `ViewController` and `ContainerViewController` is an **embed** segue. The segues between `ContainerViewController` and its two child view controllers is a **custom** segue. This custom segue is named `Empty` and is a subclass of `UIStoryboardSegue`. It contains an empty `perform` method. The `ContainerViewController` will take care of moving the child view controllers into and out of place. However, the fake segues are needed to create the connections in the storyboard. If you're like me you cringe at the thought of having a fake/empty class like this but the benefit is that it allows us to stay firmly in the world of storyboard idioms without resorting to programmatically loading isolated storyboard scenes. It's one tiny bit of ugliness which allows us to preserve the usefulness and elegance of storyboards. The storyboard still visually represents the scenes and their relationships accurately. We can still use segues to control what happens.  Drag from the view controller object to the appropriate child view controller.  Choose the `empty` segue. Interface Builder automatically lowercases the `Empty` classname and adds it to the list of available segue types.  Be sure to give identifiers to the custom segues. With the segues in place the `ContainerViewController` class has everything it needs to manage the child view controllers. Here' s the code for the `ContainerViewController` class. #import "ContainerViewController.h" #define SegueIdentifierFirst @"embedFirst" #define SegueIdentifierSecond @"embedSecond" @interface ContainerViewController () @property (strong, nonatomic) NSString *currentSegueIdentifier; @end @implementation ContainerViewController - (void)viewDidLoad { [super viewDidLoad]; self.currentSegueIdentifier = SegueIdentifierFirst; [self performSegueWithIdentifier:self.currentSegueIdentifier sender:nil]; } - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { if ([segue.identifier isEqualToString:SegueIdentifierFirst]) { if (self.childViewControllers.count > 0) { [self swapFromViewController:[self.childViewControllers objectAtIndex:0] toViewController:segue.destinationViewController]; } else { [self addChildViewController:segue.destinationViewController]; ((UIViewController *)segue.destinationViewController).view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height); [self.view addSubview:((UIViewController *)segue.destinationViewController).view]; [segue.destinationViewController didMoveToParentViewController:self]; } } else if ([segue.identifier isEqualToString:SegueIdentifierSecond]) { [self swapFromViewController:[self.childViewControllers objectAtIndex:0] toViewController:segue.destinationViewController]; } } - (void)swapFromViewController:(UIViewController *)fromViewController toViewController:(UIViewController *)toViewController { toViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height); [fromViewController willMoveToParentViewController:nil]; [self addChildViewController:toViewController]; [self transitionFromViewController:fromViewController toViewController:toViewController duration:1.0 options:UIViewAnimationOptionTransitionCrossDissolve animations:nil completion:^(BOOL finished) { [fromViewController removeFromParentViewController]; [toViewController didMoveToParentViewController:self]; }]; } - (void)swapViewControllers { self.currentSegueIdentifier = (self.currentSegueIdentifier == SegueIdentifierFirst) ? SegueIdentifierSecond : SegueIdentifierFirst; [self performSegueWithIdentifier:self.currentSegueIdentifier sender:nil]; } @end The regular `ViewController` class simply sets a reference to `ContainerViewController` so it can call the `swapViewControllers` method when the button is pressed. @interface ViewController () @property (nonatomic, weak) ContainerViewController *containerViewController; - (IBAction)swapButtonPressed:(id)sender; @end @implementation ViewController - (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender { if ([segue.identifier isEqualToString:@"embedContainer"]) { self.containerViewController = segue.destinationViewController; } } - (IBAction)swapButtonPressed:(id)sender { [self.containerViewController swapViewControllers]; } @end Hopefully, this has made some kind of sense. The full project is [available on GitHub](https://github.com/mluton/EmbeddedSwapping).

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