UITabBar shows black screen when using animated transition. (Fast)

I am making an iOS UITabBar app and I am trying to use an animated transition. But something is wrong. My app shows a black blank view when changing view with an animated transition.

My code

TransitionManager class

...
func animateTransition(transitionContext: UIViewControllerContextTransitioning) {

    let container = transitionContext.containerView()
    let fromView = transitionContext.viewForKey(UITransitionContextFromViewKey)!
    let toView = transitionContext.viewForKey(UITransitionContextToViewKey)!

    let offScreenRight = CGAffineTransformMakeTranslation(container.frame.width, 0)
    let offScreenLeft = CGAffineTransformMakeTranslation(-container.frame.width, 0)

    toView.transform = offScreenRight

    container.addSubview(toView)
    container.addSubview(fromView)

    let duration = self.transitionDuration(transitionContext)

    UIView.animateWithDuration(duration, delay: 0.0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0.8, options: nil, animations: {

        fromView.transform = offScreenLeft
        toView.transform = CGAffineTransformIdentity

        }, completion: { finished in
            transitionContext.completeTransition(true)
    })

}
...

      

        
        
        
      

    

UITabBarController

func tabBarController(tabBarController: UITabBarController, animationControllerForTransitionFromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
    var animatedTransitioningObject = TransitionManager()
    return animatedTransitioningObject
}

      

        
        
        
      

    

I will try to add this code when the transition is complete

    }, completion: { finished in
        transitionContext.completeTransition(true)
        // add this line
        UIApplication.sharedApplication().keyWindow!.addSubview(toView)
})

      

        
        
        
      

    

Now my second view displays correctly, but my panel disappears! I am trying to debug a view hierarchy. My tab bar doesn't seem to disappear. But this brings back a second look.

How to solve this problem?

ps. sorry for my bad english.