How do I stretch the view when tab is hidden

I'm using the auto layout via the storyboard.

override func viewWillAppear(animated: Bool) {

    //hide bottom bar
    self.tabBarController?.tabBar.hidden = true


}

// postload func
override func viewWillDisappear(animated: Bool) {
    self.tabBarController?.tabBar.hidden = false

}

As you can see black is tabczontroller's height..How do I stretch the view to screen's bottom?