title: How a ViewController can recognize when it is NOT onscreen
body: <p>I have two viewcontrollers which we will call VC1 and VC2.  VC1 is a splitscreencontroller that presents VC2 full-screen modal when an image or video is tapped.  VC1 implements: <code>-(void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation</code>  When VC2 is onscreen and the user rotates the device, this is recognized in the VC1 method above which is executed.  However, I have some code in that VC1 method that I don't want to execute if VC1 is not on screen.  It is otherwise fine, and indeed necessary, that the rotation method of VC1 is called.  </p>
  
  <p>What is the best way for VC1 to identify when it is not onscreen such that I can put an if statement in the rotate method that will then only execute certain statements if VC1 is actually onscreen?</p>