title: How to reuse a map view once it's rendered
body: <p>I have been searching this for a while but couldn't find a solution.</p>
  
  <p>My app has several views (pretty common ones like table or map) and i provide a menu to allow users switch between them, which is implemented with segue. i noticed that every time i switch to a map view(and other views as well) the map view will be rendered from scratch. I might not understand the term "render" perfectly. by render i mean the background starts with grey grid and then map starts showing up in pieces.</p>
  
  <p>Is there a way i can say something like: only render this map view once and all subsequent switches to this view will reuse what was rendered in the first time?</p>
  
  <p>thanks in advance for any answers!</p>
  
  <pre><code>// here is how I store a reference of target view controller
  self.tableViewController = segue.destinationViewController as UIViewController
  
  // this function does the switch
  func swapFromViewController(from:UIViewController, to:UIViewController) {
      from.willMoveToParentViewController(nil)
      self.addChildViewController(to)
      currentController = to
  
      self.transitionFromViewController(from, toViewController: to, duration: 1.0, options: UIViewAnimationOptions.TransitionCrossDissolve, animations: nil, completion: {
          (finished:Bool) -&gt; Void in
          self.transitionInProgress = false
      })
  }
  
  // function call looks like:
  self.swapFromViewController(currentController!, to: tableViewController)
  </code></pre>