title: Is didReceiveMemoryWarning / viewDidUnload called when a view controller is shown?
body: <p>A question about <code>didReceiveMemoryWarning</code> / <code>viewDidUnload</code>.</p>
  
  <p>If my app has many view controllers, one of them is shown, and the others back (because of I use a navigation controller or tab bar controller, it does not matter), which view controllers will receive <code>didReceiveMemoryWarning</code> / <code>viewDidUnload</code>, all of them, only hidden, or only shown?</p>
  
  <p>Is it possible that shown VC receives <code>didReceiveMemoryWarning</code> but not <code>viewDidUnload</code> (because as is shown, it doesn't make any sense).</p>
  
  <p>By the way, I have these questions after seeing this diagram:
  <img src="https://i.stack.imgur.com/tox6G.jpg" alt="UIViewController init/dealloc flow chart"></p>
  
  <p>Thanks a lot for help.</p>