title: Sync data between two viewcontrollers to avoid creating same observer again
body: <p>In my main VC I look for changes in my FB database like this:</p>
  
  <pre><code>ref.child("posts").observe(.childChanged, with: { (snapshot) in
    .......                
  })
  </code></pre>
  
  <p>From this VC I can enter VC2 which is set to be "present modally" in my segue.</p>
  
  <p>Now I wonder if I can pass live FB data from VC1 to VC2? I know that I can use a <code>segue.identifier</code> and pass data when I segue to the next VC but this is one time <em>send</em> only. Or should I setup a delegate to fetch data from vc1 to vc2?</p>
  
  <p>So is there any way I can send data from VC1 to VC2 once a node has been updated or must I setup a new <code>.observe()</code> function in VC2?</p>