ios - sendSubviewToBack和bringSubviewToFront导致根视图控制器的子视图向上移动并被导航栏重叠

I have a problem with sendSubviewToBack and bringSubviewToFront calls. I create UIImageView and ScrollView with several other elements (like buttons and labels) programmaticaly (only ScrollView is created in storyboard). UIImageView have to hold a background image. ScrollView and UIImageView are added as subviews of view controller (other elements are subviews of scrollview). After I create a UIImageView and set the image like this, I callI have a problem with sendSubviewToBack and bri