ContainedViewController.swift

class ContainedViewController: UIViewController {
  weak var dataDelegate: FrameViewControllerDataDelegate?

  override func willMoveToParentViewController(parent: UIViewController?) {
    super.willMoveToParentViewController(parent)
    self.dataDelegate = parent as? FrameViewControllerDataDelegate
  }
  
  override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    self.dataDelegate?.reloadData()
  }
}

extension ContainedViewController: FrameViewControllerDataType {
  var titleText: String? {
    return "Hello World"
  }
}

FrameViewController.swift

class FrameViewController: UIViewController {
  @IBOutlet var titleLabel: UILabel!
  var dataSource: FrameViewControllerDataType?
  
  override func addChildViewController(childController: UIViewController) {
    super.addChildViewController(childController)
    self.dataSource = childController as? FrameViewControllerDataType
  }
}

protocol FrameViewControllerDataType {
  var titleText: String? { get }
  var dataDelegate: FrameViewControllerDataDelegate? { get set }
}

protocol FrameViewControllerDataDelegate: class {
  func reloadData() -> Void
}

extension FrameViewController: FrameViewControllerDataDelegate {
  func reloadData() {
    self.titleLabel.text = self.dataSource?.titleText
  }
}