title: how to create bottom nav bar with dynamic floating action button with good animation flutter?
body: <p>I would like to create a custom bottom nav bar with a changed floating action button like this:</p>
  <p><a href="https://i.stack.imgur.com/TueRk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TueRk.png" alt="enter image description here" /></a></p>
  <p>and when change tab it will be like this with nice and ease animation:</p>
  <p><a href="https://i.stack.imgur.com/fJ0mX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fJ0mX.png" alt="enter image description here" /></a></p>
  <p>any suggestions how we can built it.</p>