title: Flutter: How to use AnimatedContainer with Expanded in Column?
body: <p>Let's say we have 3 children of a <code>Column</code>:</p>
  
  <pre><code>Flexible(
     flex:1,
     child: Container(
        color: Colors.red,
     ),
  ),
  Flexible(
     flex:3,
     child: Container(
        color: Colors.yellow,
     ),
  ),
  Flexible(
     flex:1,
     child: Container(
        color: Colors.blue,
     ),
  ),
  </code></pre>
  
  <p>I want to programmatically expand middle child with <code>flex=3</code> to cover the whole <code>Column</code> with smooth animation, while the top and bottom children shrinks accordingly.</p>
  
  <p>Right now my setup is with a <code>Column</code> and <code>Flexible</code> widgets. However if you can think of a solution with other widgets, I am open to those ideas as well. </p>