Horizontally Centering Focused UIButton

MasteringFocusExample5.swift

class ActionHeroesView: UIView {
  let stalloneButton: UIButton
  let vanDammeButton: UIButton
  
  // ...

  override func didUpdateFocusInContext(context: UIFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
    super.didUpdateFocusInContext(context, withAnimationCoordinator: coordinator)
    
    // we'll center Stallone when neither is in focus since he's a bigger deal
    let vanDammeFocused = (context.nextFocusedView == vanDammeButton)
    
    layoutIfNeeded()
    
    coordinator.addCoordinatedAnimations({
        self.stalloneCenterXConstraint.active = !vanDammeFocused
        self.vanDammeCenterXConstraint.active = vanDammeFocused
    
        self.layoutIfNeeded()
      },
      completion: nil
    )
  }
}