title: Keeping Firebase DB listeners active when view controller isn't active
body: <p>I have an iOS app with the <code>Firebase</code> <code>Listener</code> on the home screen <code>viewController</code>.</p>
  
  <p>However, when the app is in the <code>background</code>, or the user is on a different <code>viewController</code>, the <code>listener</code> don't update - the data rush back when the <code>viewController</code> re-opens.</p>
  
  <p>The <code>Firebase DB</code> data is used across the entire app, so I want to have the data constantly up to date <strong>(preferably while the app is in the <code>background</code> too)</strong>.</p>
  
  <p>This problem is especially prevalent when the user receives a <code>push notification</code> of new data, but the user can't see it in the app because it hasn't yet downloaded (the only other option would be to send the data with the push message but I'd prefer to avoid this)</p>