AnimatedBuilder({Key key, @required Animation<Object> animation, @required TransitionBuilder builder, Widget child })

Creates an animated builder.

The animation and builder arguments must not be null.

Source 

AnimatedBuilder({
  Key key,
  @required Animation<Object> animation,
  @required this.builder,
  this.child
}) : super(key: key, animation: animation) {
  assert(builder != null);
}