title: How to get size of a component in react-native?
body: <p>I know there's </p>
  
  <pre><code>Dimensions.get('window');
  </code></pre>
  
  <p>But what about a arbitrary view that has no dim string? The arbitrary view could have many subviews. The size of the view is decided by style and layout of the subviews, and it's hard to calculate the size from subviews.</p>