AnimatedPositioned({Key key, Widget child, double left, double top, double right, double bottom, double width, double height, Curve curve: Curves.linear, @required Duration duration })

Creates a widget that animates its position implicitly.

Only two out of the three horizontal values (left, right, width), and only two out of the three vertical values (top, bottom, height), can be set. In each case, at least one of the three must be null.

The curve and duration arguments must not be null.

Source 

AnimatedPositioned({
  Key key,
  this.child,
  this.left,
  this.top,
  this.right,
  this.bottom,
  this.width,
  this.height,
  Curve curve: Curves.linear,
  @required Duration duration,
}) : super(key: key, curve: curve, duration: duration) {
  assert(left == null || right == null || width == null);
  assert(top == null || bottom == null || height == null);
}