title: How to measure dimensions of a widget using Offstage?
body: <p><a href="https://api.flutter.dev/flutter/widgets/Offstage-class.html" rel="nofollow noreferrer">Docs</a> says:</p>
  
  <blockquote>
    <p>Offstage can be used to measure the dimensions of a widget without bringing it on screen (yet)</p>
  </blockquote>
  
  <p>How can I measure the dimensions using <code>Offstage</code>?</p>