tvOS detect tabbar show/hide in Swift

viewcontroller.swift

override func didUpdateFocusInContext(context: UIFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
    let prevFocusViewClassName = NSStringFromClass(context.previouslyFocusedView!.classForCoder)
    let nextFocusedView = NSStringFromClass(context.nextFocusedView!.classForCoder)
    let barButtonName = "UITabBarButton"
    
    if prevFocusViewClassName == barButtonName && nextFocusedView != barButtonName {
        // Tabbar disappeared
    } else if prevFocusViewClassName != barButtonName && nextFocusedView == barButtonName {
        // Tabbar appeared
    }
}