title: Animate position of a widget in Flutter
body: <p>I would like to animate the position of an icon widget on the screen. The problem is that I don't know the end position of widget until the whole screen has finished building.</p>
  
  <p>This sketch illustrates what I want to achieve:
  <a href="https://i.stack.imgur.com/cdbHR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cdbHR.png" alt="enter image description here"></a>
  <br>The icon should start out from the centre of the screen and end up in middle of the space available above the text field and button. The text field and the button themselves are centred in the screen.</p>
  
  <p>How can I achieve this?</p>