//扩展TabBarController使TabBar可以隐藏显示
extension UITabBarController {
    
    func setTabBarVisible(visible:Bool, animated:Bool) {
        
        // bail if the current state matches the desired state
        if (tabBarIsVisible() == visible) { return }
        
        // get a frame calculation ready
        let frame = self.tabBar.frame
        let height = frame.size.height
        let offsetY = (visible ? -height : height)
        
        // animate the tabBar
        UIView.animateWithDuration(animated ? 0.3 : 0.0) {
            self.tabBar.frame = CGRectOffset(frame, 0, offsetY)
            self.view.frame = CGRectMake(0, 0, self.view.frame.width, self.view.frame.height + offsetY)
            self.view.setNeedsDisplay()
            self.view.layoutIfNeeded()
        }
    }
    
    func tabBarIsVisible() ->Bool {
        return self.tabBar.frame.origin.y < CGRectGetMaxY(self.view.frame)
    }
}

使用上面的代码隐藏UITabBar页面使用presentViewController跳转到另一个ViewController再回来，
页面底部就出现了一个白匡，求如何解决？