title: Flutter: Using the SlideTransition
body: <p>I'm confused on how to use the SlideTransition, especially about the Position property. Atm I've got an AnimationBuilder in which I want to use a SlideTransition and an AnimationController. How would I get the position of the child of the AnimationBuilder? Or is that not what has to be passed to the Position property?
  Perhaps a small example would help!</p>