title: Best way to determine that a UIViewController has been loaded, and has a valid view?
body: <p>When the view property of a UIViewController is accessed, it first checks to see if it's got an existing view, and returns that. If not, it loads its nib or calls -loadView. </p>
  
  <p>When a controller receives a -didReceiveMemoryWarning message, the default behavior is to remove that cached view (assuming it's not in use at the time). </p>
  
  <p>If I override -didReceiveMemoryWarning, how can I determine whether the view has been cleared? My understanding is that the default implementation checks to see if self.view.superview == nil. If so, it clears the cached view. Of course, it first checks to see if there <em>is</em> a cached view, and if not, it does nothing. However, I, as a subclass, can't call self.view.superview, for if there <em>isn't</em> a view, it'll generate one.</p>
  
  <p>So, how do I figure out if _view exists? (I can't just look at _view; I get linking errors when building for the device).</p>