title: How to check if a widget/page is rendered?
body: <p>Is there anything like <code>componentWillDisapear()</code> in RN?</p>
  <p>Details of my issue:</p>
  <p>I have two screens: Home and Details. My application uses 'firebase_admob' for adverts and the 'firebase_admob' (see the screenshot below) can render only fixed banner for the whole application. So when you go to other screens you see it too, but I need it only at Home screen. It means, when user navigates to Details I have to hide it. How to do it?</p>
  <p>Note: I want to call <code>dispose()</code> when a user leaves the Home screen. To render the banner you need to call <code>show()</code> in <code>BannerAd</code> class and when you need to hide you just call dispose.</p>
  <p><a href="https://i.stack.imgur.com/TMfej.png" rel="noreferrer"><img src="https://i.stack.imgur.com/TMfej.png" alt="enter image description here" /></a></p>