title: react native how to check if Component current show in screen
body: <p>In my React native' project i need to check when component is shown in screen to update UI by background thread.</p>
  
  <p>I have look around component props specs and  try <code>componentWillUnmount</code>,<code>componentWillMount</code> but it not working in my case.</p>
  
  <p>I have try using <code>navigator.getCurrentRoutes()</code> too, but it return empty object.</p>
  
  <p>Please help me solve this case!.</p>