Access Container View Controller from Parent iOS

in iOS6 I noticed the new Container View but am not quite sure how to access it's controller from the containing view.

Scenario:

I want to access the labels in Alert view controller from the view controller that houses the container view.

There's a segue between them, can I use that?

Yes, you can use the segue to get access the child view controller (and its view and subviews). Give the segue an identifier (such as alertview_embed), using the Attributes inspector in Storyboard. Then have the parent view controller (the one housing the container view) implement a method like this:

- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
   NSString * segueName = segue.identifier;
   if ([segueName isEqualToString: @"alertview_embed"]) {
       AlertViewController * childViewController = (AlertViewController *) [segue destinationViewController];
       AlertView * alertView = childViewController.view;
       // do something with the AlertView's subviews here...
   }
}

You can do that simply with self.childViewControllers.lastObject (assuming you only have one child, otherwise use objectAtIndex:).

for Swift Programming

you can write like this

var containerViewController: ExampleViewController?
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    // you can set this name in 'segue.embed' in storyboard
    if segue.identifier == "checkinPopupIdentifierInStoryBoard" {
        let connectContainerViewController = segue.destinationViewController as ExampleViewController
        containerViewController = connectContainerViewController
    }
}

The prepareForSegue approach works, but it relies on the segue identifier magic string. Maybe there's a better way.

If you know the class of the VC you're after, you can do this very neatly with a computed property:

var camperVan: CamperVanViewController? {
  return childViewControllers.flatMap({ $0 as? CamperVanViewController }).first
  // This works because `flatMap` removes nils
}

This relies on childViewControllers. While I agree it could be fragile to rely on the first one, naming the class you seek makes this seem quite solid.

An updated answer for Swift 3, using a computed property:

var jobSummaryViewController: JobSummaryViewController {
    get {
        let ctrl = childViewControllers.first(where: { $0 is JobSummaryViewController })
        return ctrl as! JobSummaryViewController
    }
}

This only iterates the list of children until it reaches the first match.

self.childViewControllers is more relevant when you need control from the parent. For instance, if the child controller is a table view and you want to reload it forcefully or change a property via a button tap or any other event on Parent View Controller, you can do it by accessing ChildViewController's instance and not via prepareForSegue. Both have their applications in different ways.

There is another way using Swift's switch statement on the type of the view controller :

override func prepare(for segue: UIStoryboardSegue, sender: Any?)
{
  switch segue.destination
  {
    case let aViewController as AViewController:
      self.aViewController = aViewController
    case let bViewController as BViewController:
      self.bViewController = bViewController
    default:
      return
  }
}

I use Code like:

- (IBAction)showCartItems:(id)sender{ 
  ListOfCartItemsViewController *listOfItemsVC=[self.storyboard instantiateViewControllerWithIdentifier:@"ListOfCartItemsViewController"];
  [self addChildViewController:listOfItemsVC];
 }

In case someone is looking for Swift 3.0,

viewController1, viewController2 and so on will then be accessible.

let viewController1 : OneViewController!
let viewController2 : TwoViewController!

// Safety handling of optional String
if let identifier: String = segue.identifier {

    switch identifier {

    case "segueName1":
        viewController1 = segue.destination as! OneViewController
        break
            
    case "segueName2":
        viewController2 = segue.destination as! TwoViewController
        break
            
    // ... More cases can be inserted here ...

    default:
        // A new segue is added in the storyboard but not yet including in this switch
        print("A case missing for segue identifier: \(identifier)")
        break
    }
        
} else {
    // Either the segue or the identifier is inaccessible 
    print("WARNING: identifier in segue is not accessible")
}

With generic you can do some sweet things. Here is an extension to Array:

extension Array {
    func firstMatchingType<Type>() -> Type? {
        return first(where: { $0 is Type }) as? Type
    }
}

You can then do this in your viewController:

var viewControllerInContainer: YourViewControllerClass? {
    return childViewControllers.firstMatchingType()!
}

you can write like this

- (IBAction)showDetail:(UIButton *)sender {  
            DetailViewController *detailVc = [self.childViewControllers firstObject];  
        detailVc.lable.text = sender.titleLabel.text;  
    }  
}